bluuebunny/crossref_metadata_2025 huggingface dataset:
A Vibration-Based Structural Damage Detection Method and its Applications to Engineering Structures
Authors: He K. , Zhu W. D.
Published: August 2012

Two major challenges associated with a vibration-based damage detection method using changes in natural frequencies are addressed: accurate modeling of structures and the development of a robust inverse algorithm to detect damage, which are defined as the forward and inverse problems, respectively. To resolve the forward problem, new physics-based finite element modeling techniques are developed for fillets in thin-walled beams and for bolted joints, so that complex structures can be accurately modeled with a reasonable model size. To resolve the inverse problem, a logistic function transformation is introduced to convert the constrained optimization problem to an unconstrained one, and a robust iterative algorithm using the Levenberg-Marquardt method is developed to accurately detect the locations and extent of damage. The new methodology can ensure global convergence of the iterative algorithm in solving under-determined system equations and deal with damage detection problems with relatively large modeling error and measurement noise. It is applied to various engineering structures including lightning masts, a space frame structure and one of its components, and a pipeline. The exact locations and extent of damage can be detected in the numerical simulation, and the locations and extent of damage can be successfully detected in experimental damage detection.
A Kriging-Simulated Annealing Meta-Algorithm for Optimization of Convective Heat Transfer in a Grooved Channel
Authors: Cadirci Sertac , Akguc Alpay , Gunes Hasan
Published: August 2012

As computational fluid dynamics (CFD) simulations still take a lot of time in industry for design optimization analyses, we propose to reduce the number of required CFD simulations considerably using a new meta-algorithm. The algorithm consists of employing kriging in conjunction with simulated annealing (SA) as a design tool. The method enables effective and fast design optimization for complex fluid flow systems. In this paper, it is applied to a convective heat transfer problem in a channel with periodic heat sources with constant heat flux. We show that the geometry optimization of two dimensional thermo-fluids problems in complex geometries is made more effective and faster using kriging-simulated annealing meta-algorithm.
Performance Degradation of the MEMS Vibratory Gyroscope in Harsh Environments
Authors: Patel Chandradip , McCluskey Patrick
Published: August 2012

The use of MEMS gyroscopes in a wide range of applications requiring then to function from medium to harsh environments make it necessary to evaluate the performance of MEMS gyroscopes under those conditions. This paper focuses on the effects of elevated temperature and humidity on the performance of MEMS vibratory gyroscopes. Performance of the MEMS gyroscope was evaluated by conducting Highly Accelerated Stress Testing (HAST) on a COTS (commercial-off-the-shelf) single axis MEMS vibratory gyroscope having an operating temperature range from −40C to +105C. The gyroscope sensors were exposed to 130°C and 85% relative humidity with a pressure of 33.3 psia or 230 kPa for 96 hours. Pre-baking and post-baking tests were conducted before and after HAST at 125C for 24 hours respectively. Also, stationary baseline testing (SBT) and rotary baseline testing (RBT) were performed before and after the pre-baking, HAST and post-baking tests to measure any permanent shift during the respective test. A preliminary result shows that the MEMS gyroscope output degraded in the pre-baking test and HAST; while it showed a recovery in post-baking test. After completing the entire test procedure, it was observed that MEMS gyroscope output didn’t come back to the original position, and resulted in a permanent output shift of 1.85deg/s.
Thermal Characteristics of Flashing Spray of Volatile R134a Cryogens
Authors: Zhou Z.-F. , Wu W.-T. , Wang G.-X. , Gong Z. , Chen B. , Wang Y.-S. , Guo L.-J.
Published: August 2012

This paper presents an experimental investigation of thermal behavior of flashing spray of refrigerant R134a. A high-speed camera up to 1000 frames per second is used to visualize the shape and size of the spray and an infrared thermograph is employed to visualize the temperature variation of the spray. The temperature field within the spray is measured by a small thermocouple whose position can be systematically adjusted to cover the entire spray. The high-speed photo images of sprays revealed an explosive spray formation near the exit of nozzle and the formation of a hot core region near the nozzle. The measurements found that the hot core region was quickly dissipated, followed by a cold region of almost uniform temperature that is far below the saturation point of R134a at the ambient pressure. The measurements provide detailed quantitative information of both radial and axial temperature distributions of droplets within the spray. These results provide insight into the formation of flashing spray of volatile liquids.
Particle Resuspension From Carpeted Floorings in Indoor Environment in Turbulent Flows
Authors: Goldasteh Iman , Ahmadi Goodarz , Ferro Andrea
Published: August 2012

Particle resuspension is an important source of particulate matter in the indoor environment. [1] In this study, a model for resuspension of spherical particles from carpet fibers was developed using the micro-roughness model for simulating the adhesion of rough spherical particles. The Johnson-Kendall-Roberts (JKR) adhesion model was used for modeling the adhesion force between particles and carpet fibers. Adhesion of pollen particles to the carpet fibers was studied, and the pull-off forces predicted by the model are compared with the available experimental data. The effect of the hydrodynamic force of fluid flow on resuspension of particles under turbulent flow conditions was studied and the effect of turbulence bursts was included in the model. In particular, the range of airflow velocity for resuspension of pollen particles from carpet was evaluated and the results are presented in graphical form. The role of airflow on resuspension of particles from carpeted floorings is discussed.
Heat Transfer due to Microscale Thin Film Evaporation From the Steady State Meniscus in a Coherent Porous Silicon Based Micro-Columnated Wicking Structure
Authors: Dhillon Navdeep S. , Cheng Jim C. , Pisano Albert P.
Published: August 2012

A numerical fluid flow and heat transfer model is presented in order to study the evaporation characteristics of a stationary thin film liquid-vapor meniscus. The model is used to evaluate the evaporative heat transfer performance of micron-size rectangular channels on the surface of the secondary wick, inside a micro-columnated coherent porous silicon wick design. The shape of the liquid-vapor meniscus in the channel is obtained by solving the Young-Laplace equation, using a surface energy minimizing algorithm. Mass, momentum and energy equations are then solved in the liquid domain using a discrete finite volume method-based approach. The vapor is assumed to be fully saturated and evaporation at the liquid-vapor interface is modeled using kinetic theory. The effect of wall superheat and inlet-liquid subcooling on the rate of evaporation and associated heat transfer from the evaporating meniscus is characterized.
Static Nano-Control of Cantilever Beams Using the Inverse Flexoelectric Effect
Authors: Hu S. D. , Li H. , Tzou H. S.
Published: August 2012

Flexoelectricity, an electromechanical coupling effect, exhibits two opposite electromechanical properties. One is the direct flexoelectric effect that mechanical strain gradient induces an electric polarization (or electric field); the other is the inverse flexoelectric effect that polarization (or electric field) gradient induces internal stress (or strain). The later can serve as an actuation mechanism to control the static deformation of flexible structures. This study focuses on an application of the inverse flexoelectric effect to the static displacement control of a cantilever beam. The flexoelectric layer is covered with an electrode layer on the bottom surface and an AFM probe tip on the top surface in order to generate an inhomogeneous electric field when powered. The control force induced by the inverse flexoelectric effect is evaluated and its spatial distribution resembles a Dirac delta function. Therefore, a “buckling” characteristic happens at the contact point of the beam under the inverse flexoelectric control. The deflection results of the cantilever beam with respect to the AFM probe tip radius indicate that a smaller AFM probe tip achieves a more effective control effect. To evaluate the control effectiveness, the flexoelectric deflections are also compared with those resulting from the converse piezoelectric effect. It is evident that the inverse flexoelectric effect provides much better localized static deflection control of.flexible beams.
Gate-Free Graphene-Based Sensor for pH Monitoring
Authors: Lei Nan , Li Pengfei , Xue Wei , Xu Jie
Published: August 2012

Graphene, as an ideal two-dimensional material, holds great potential for building high-performance sensors. Traditional microfabrication processes, such as lithography and etching, often require multiple complex steps including masking and aligning. Moreover, the graphene is often configured as the semiconducting material in transistors, which add complexity to the system. In this paper, we report the fabrication and characterization of a simple gate-free graphene device. The graphene sheets are made by mechanical exfoliation from bulk graphite and then placed onto a silicon wafer with a thermal oxidization layer. Platinum contact electrodes are fabricated with a mask-free process using focused ion beam, and then expanded by silver paint. An annealing process is used to improve the electrical contact. During the experiment, the fabricated graphene device is used to sense different pH values in the surrounding liquid environment. The results show that the conductance of the graphene increases quadratically with the increasing pH values, which makes the device a high-sensitivity pH sensor. In the end, the possible sensing mechanisms of our graphene device are discussed.
Acoustic Manipulation of Particles in Variously Shaped Liquid Droplets
Authors: Yu Gan , Chen Xiaolin , Xu Jie
Published: August 2012

The ability to precisely trap, transport and manipulate micrometer-sized objects, including biological cells, DNA-coated microspheres and microorganisms, is very important in life science studies and biomedical applications. In this study, acoustic radiation force in an ultrasonic standing wave field is used for micro-objects manipulation. Free surfaces of liquid droplets are used as sound reflectors to confine sound waves inside the droplets. Two techniques were developed for the precise control of droplet shapes: edge pinning and hydrophilic/hydrophobic interface pinning. For all tested droplet shapes, including circular, annular and rectangular, our experiments show that polymer micro particles can be manipulated by ultrasound and form into a variety of patterns, for example, concentric rings and radial lines in an annular droplet. The complexity of the pattern increases with increasing frequency, and the observations are in line with simulation results. The acoustic manipulation technique developed here has the potential to be integrated into a more complex on-chip microfluidic circuit. Especially because our method is well compatible with electrowetting technology, which is a powerful tool for manipulating droplets with free surfaces, the combination of the two methods can provide more versatile manipulation abilities and may bring a wealth of novel applications.
Numerical Studies of Thermoacoustic Convection in Near-Critical Fluids
Authors: Hasan Nusair , Farouk Bakhtier
Published: August 2012

Thermoacoustic convection in carbon dioxide near its critical point is investigated numerically. A real-fluid model has been developed taking into account all the relevant fluid property variations near the critical point, including the bulk viscosity. The thermo-physical properties of the near-critical supercritical fluids are given as functions of both pressure and temperature due to their strong divergence near the critical point. As a layer of supercritical fluid is heated rapidly, the combination of very high thermal compressibility and vanishing thermal diffusivity near the critical points of fluids affect thermal energy propagation, leading to the formation of acoustic waves as carriers of thermal energy. The rapidity of the boundary heating is a key factor in the generation of these acoustic waves. We also study the effect of different rates of boundary heating for the temperature equilibration mechanism near the critical point. As the critically diverging bulk viscosity plays a significant role on the transport processes near the critical point, effect of bulk viscosity on the flow field and heat transport induced by thermoacoustic waves and buoyancy in supercritical fluids is also investigated numerically. The predicted results from the present study can be utilized to understand the thermal transport mechanism in near-critical fluids.
Simulation of Backward Film Cooling at Gas Turbine Operating Conditions With and Without Mist Injection
Authors: Subbuswamy Ganesh , Li Xianchang
Published: August 2012

The cooling of gas turbines is critical for engines’ efficiency as well as safety and lifetime. Film cooling has been used to cool the turbine blades for many years. The main issues related to film cooling are its poor coverage, aerodynamic loss, and increase of heat transfer coefficient due to strong flow mixing. To overcome these problems, film cooling with backward injection has been found to produce a more uniform cooling coverage under low pressure and temperature conditions and with simple cylindrical holes. The performance of film cooling with backward injection at gas turbine operating conditions is studied with numerical simulation in this paper. Effects of the blowing ratios and angles are examined. It is seen that the cooling coverage is generally much more uniform by using backward injection at gas turbine operating conditions, and in some cases the film cooling effectiveness can be almost doubled when compared to forward injection. The backward injection also shows its advantage when the blowing angle and blowing ratio change. However, mist (droplets) injection does not affect the cooling performance of the backward jet at the conditions under study. The best case of film cooling in this study is the fan-shaped hole with backward injection.
Computational Fluid Dynamics Using Graphics Processing Units: Challenges and Opportunities
Authors: Vanka S. Pratap , Shinn Aaron F. , Sahu Kirti C.
Published: August 2012

A new paradigm for computing fluid flows is the use of Graphics Processing Units (GPU), which have recently become very powerful and convenient to use. In the past three years, we have implemented five different fluid flow algorithms on GPUs and have obtained significant speed-ups over a single CPU. Typically, it is possible to achieve a factor of 50–100 over a single CPU. In this review paper, we describe our experiences on the various algorithms developed and the speeds achieved.
A Microstructure-Based Model for Superplastic Deformation and Damage in Magnesium Alloys
Authors: Askari Hesamaldin , Lu Hao , Zbib Hussein , Khaleel Mohammed , Kridli Ghassan
Published: August 2012

The need to produce fuel efficient vehicles and reduced emissions has led the automotive industries to the use of the lightweight materials. The use of magnesium alloys through superplastic forming is very promising for this goal while it makes the manufacturing part less complex and reduces the weight of the parts extensively. Aside to their strength and ductility, magnesium alloys still need a major improvement to be studied before they can be considered as lightweight materials in automotive industries. That improvement is in fact developing the best thermo-mechanical processing approach considering several aspects of the microstructure and modeling and optimization of the deformation process. The objective of this study is to establish such a constitutive model and using this model to effectively obtain the optimum loading path and processing temperature to avoid local thinning and rupture of the material. This constitutive model integrates the effects of microstructural dynamics and their evolution with other continuum properties such as flow rule, hardening, temperature and strain rate.
Simulation of Laminar Liquid Jets in Gaseous Crossflow Before the Onset of Primary Breakup
Authors: Ng C.-L. , Sallam K. A.
Published: August 2012

The deformation of laminar liquid jets in gaseous crossflow before the onset of primary breakup is studied motivated by its application to fuel injection in jet afterburners and agricultural sprays, among others. Three crossflow Weber numbers that represent three different liquid jet breakup regimes; column, bag, and shear breakup regimes, were studied at large liquid/gas density ratios and small Ohnesorge numbers. In each case the liquid jet was simulated from the jet exit and ended before the location where the experimental data indicated the onset of breakup. The results show that in column and bag breakup, the reduced pressures along the sides of the jet cause the liquid to move to the sides of the jet and enhance the jet deformation. In shear breakup, the flattened upwind surface pushes the liquid towards the two sides of the jet and causing the gaseous crossflow to separate near the edges of the liquid jet thus preventing further deformation before the onset of breakup. It was also found out that in shear breakup regime, the liquid phase velocity inside the liquid jet was large enough to cause onset of ligament formation along the jet side, which was not the case in the column and bag breakup regimes. In bag breakup, downwind surface waves were observed to grow along the sides of the liquid jet triggered a complimentary experimental study that confirmed the existence of those waves for the first time.
Modeling of a Supersonic Ejection, Pilot Protection System
Authors: Crawford B. Grant , Byers Lynn K. , Fenley Quinton J.
Published: August 2012

Supersonic Ejection has always been dangerous for pilots to attempt due to the extreme aerodynamic forces acting on the body. Previous solutions to this problem have been too heavy and/or too dangerous for fighter aircraft applications. In response to a request by Boeing Defense, Space and Security, this paper proposes a system that uses the aircraft’s canopy as a ballistic shield to protect the pilot from the windblast in the initial stages of a supersonic ejection at Mach 1.4 and an altitude of 30,000 feet. Results show that the thrust needed for an ejection of this type is approximately 3,372 lbf for .75 seconds. The heaviest pilot will move 53 meters away from the aircraft, while the lightest pilot will only experience acceleration 6.6 times the acceleration due to gravity in the vertical direction. In the longitudinal direction (direction of flight), the lightest pilot will experience a deceleration of 26.2 times the acceleration due to gravity for an ejection at mach 1.4 and an altitude of 30,000 ft. While the maximum value for jerk found in this model falls within safe limits for the pilot, the simulation does not accurately model transient phenomena. This paper concludes that further research, modeling, and testing could produce a viable option for safe ejection from fighter aircraft at supersonic speeds primarily using existing components.
Analysis of Sound Attenuation in Elliptical Chamber Mufflers by Using Green’s Functions
Authors: Banerjee Subhabrata , Jacobi Anthony M.
Published: August 2012

The present work aims at finding the transmission loss of an elliptical expansion chamber, the inlet and outlet of which are located at arbitrary locations of the chamber, i.e. the side wall or on the face of the muffler. The analysis is based on the Green’s function solution for an elliptical cavity with homogeneous boundary conditions. Solving field problems with elliptical geometries require the computation of Mathieu and modified Mathieu functions. These are the eigenfunctions of the wave equation in elliptical coordinates and their computations pose a considerable challenge. In our present study, we have tried to develop a formulation for finding the transmission loss using the properties of the Mathieu and the modified Mathieu functions. The Green’s function is found by considering the boundary to be rigid walls with homogeneous boundary conditions. The inlet and outlet are assumed to be uniform velocity piston sources. The velocity potential inside the muffler is found by adding the individual potentials arising from the inlet and outlet pistons. The pressure in the chamber is obtained from the velocity potential through the linear momentum equation. The pressure at the inlet and at the outlet is approximated by the averaging the acoustic pressure over the piston area. The four-pole parameter is derived from the average pressure values and hence the transmission loss is calculated. The results are compared to those available in literature. It is shown that the results obtained from the present work agree well with those reported in literature.
Effect of Porous Media Properties on Heat Transfer in Triangular Porous Ducts With Iso-Flux Walls
Authors: Mortazavi S. Negin , Hassanipour Fatemeh
Published: August 2012

This study presents an analysis of forced convection in a porous triangular channel. The flow is assumed to have constant properties and the porous channel is an isotropic matrix. The flow is laminar and fully developed and the boundary conditions are fixed with a constant heat flux. In this paper, the accurate analytical solutions are presented to obtain the effects of porosity and permeability on the velocity and temperature distribution in a triangular channel along with the friction factor fRe, and Nusselt number NuH. The momentum and energy equations include the term of Darcy, effective viscosity and apex angel. So, the flow velocity and temperature distribution have been investigated in porous media with different properties. The Galerkin method has been applied to solve the equations accurately by considering a weight function for no slippery and isothermal wall boundary conditions. Temperature and velocity distribution and heat transfer coefficient have been obtained and compared with the same flow situation in rectangular channels.
Unified Creep Plasticity Damage (UCPD) Model for Solder
Authors: Neilsen Michael , Vianco Paul
Published: August 2012

A unified creep plasticity damage (UCPD) model for Sn-Pb and Pb-free solders was developed and implemented into finite element analysis codes. The new model will be described along with the relationship between the model’s damage evolution equation and an empirical Coffin-Manson relationship for solder fatigue. Next, two significant developments were needed to model crack initiation and growth in solder joints. First, an ability to accelerate the simulations such that the effects of hundreds or thousands of thermal cycles could be modeled in a reasonable amount of time was needed. This was accomplished by applying a user prescribed acceleration factor to the damage evolution; then, damage generated by an acceleration factor of cycles could be captured by the numerical simulation of a single thermal cycle. Second, an ability to capture the geometric effects of crack initiation and growth was needed. This was accomplished by replacing material in finite elements that had met the cracking failure criterion with very flexible elastic material. This diffuse crack modeling approach with local finite elements is known to generate mesh dependent solutions. However, introduction of an element size dependent term into the damage evolution equation was found to be effective in controlling mesh dependency. Finally, experimentally observed cracks in a typical solder joint subjected to thermal mechanical fatigue are compared with model predictions.
Electrostatically Actuated Coupled MEMS Resonators
Authors: Caruntu Dumitru I. , Taylor Kyle N.
Published: August 2012

This paper deals with the nonlinear response of an electrostatically actuated cantilever beam system composed of two micro beam resonators near natural frequency. The mathematical model of the system is obtained using Lagrange equations. The equations of motion are nondimensionalized and then the method of multiple scales is used to find steady state solutions. Both AC and DC actuation voltages of the first beam are considered, while the influence on the system of DC on the second beam is explored. Graphical representations of the influence of the detuning parameters are provided for a typical micro beam system structure.
Design of an Organic Rankine Cycle for Waste Heat Recovery From a Portable Diesel Generator
Authors: Cogswell Frederick J. , Gerlach David W. , Wagner Timothy C. , Mulugeta Jarso
Published: August 2012

A 5-kW Organic Rankine Cycle (ORC) was designed for mobile 60-kW diesel engine waste heat recovery applications to provide additional electricity for powering air conditioners. The ORC uses a non-flammable, near-zero-global-warming-potential fluid (Novec649) in a supercritical cycle. The system conceptual design and some observations on the component specification are described. The system will utilize an advanced oil-free high speed direct drive turbine. The proposed power generation module has a volume of ∼3 ft3 and contains the turbine, generator, pump, recuperator, and electrical components. The heat rejection heat exchanger is located on the power generation module in a configuration similar to mini-split air conditioners. The heat recovery heat exchanger (supercritical heater) is attached to the diesel generator and placed in series before the OEM muffler. The supercritical heater must be carefully designed to prevent the refrigerant from overheating, while still maintaining a high effectiveness.
Normal-Mode and Lumped Mass Assessment of Acoustic Degassing of Liquid Metals in an Inductively Heated Cylindrical Furnace
Authors: Shi Yinghui , Petrykowski John C.
Published: August 2012

In a number of aerospace materials processing applications, including float zone refining of electronic materials, forming of metallic glasses and induction melting of light alloys, time-dependent electromagnetic forces associated with the processing are found to influence surface shape, nucleation of precipitates, evolution of crystal nucleation sites, segregation of alloy components, grain refinement and degassing. For this last action, which finds its prime occurrence in specially designed induction furnaces, the scale up from test stand to prototype is especially sensitive to a detuning that can occur when a common set point is sought for optimizing the concomitant electrical and mechanical performance of the system. This paper outlines a continuum based model that can be used to identify a favorable set of operating conditions so that an effective and efficient, electromagnetically-induced vibrational degassing operation can proceed within the furnace. The optimization metric utilizes a coupled magnetoacoustic system of governing equations, which is subsequently solved to obtain the dynamic response of a molten metallic to an eddy current-type excitation. The solutions display both a transient and steady state response, as well as eigenmode and eigenfrequency characteristics which capture both the spectral signatures of the furnace as well as the optimum operating conditions for degassing. The solutions are obtained with the aid of higher transcendental functions of Bessel type, generated within a MATLAB environment. A set of operating conditions is identified which would promote optimal degassing for light alloys in commercial size induction furnaces. The magnetic field model embedded in the solution is sufficiently general to allow for use in analyzing a DC field biasing method which has recently shown promise for use in grain refinement and metallic glass forming applications for which the characteristics of the vibrational field can be utilized to effectively diminish crystal nucleation.
Annealing Temperature Effect on the Structure of High Thermal Conductivity Silver/Epoxy Nanocomposites
Authors: Pashayi Kamyar , Fard Hafez Raeisi , Lai Fengyuan , Plawsky Joel , Borca-Tasciuc Theodorian
Published: August 2012

The thermal conductivity κ of polymer nanoparticle composites is typically <10 Wm−1K−1, even when high κ nanofillers are employed, due to the thermal interface resistance between nanoparticles and the polymer matrix1 or the absence of high thermal conductivity pathways. We recently demonstrated high κ in bulk nanocomposites of silver nanoparticles dispersed in epoxy and cured at low temperature (150 °C). A nanocomposite with 30 vol. % 20nm particles exhibited κ ∼30 Wm−1K−1.2 The mechanism responsible for enhancing κ was found to be the self-construction, through in-situ sintering, of high aspect ratio metallic networks inside the nanocomposite.2 In order to control and optimize the network structure and subsequently increase κ even further, this work focuses on studying the effects of curing temperature and nanoparticle surface coating on the structure of the nanocomposite.
Promoting or Suppressing Transition to Weak Turbulence in Porous Media Convection via Feedback Control
Authors: Vadasz Peter
Published: August 2012

A method of using feedback control to promote or suppress the transition to chaos in porous media convection is demonstrated in this paper. Feedback control is used in the present paper to provide a comparison between an analytical expression for the transition point to chaos and numerical results. In addition it is shown that such a feedback control can be applied as an excellent practical means for controlling (suppressing or promoting) chaos by using a Magyari transformation. The latter shows that the controlled model can be transformed into the uncontrolled one via a simple transformation of variables implying that the main effect the feedback control has on the solution is equivalent to altering the initial conditions. The theoretical and practical significance of such an equivalent alteration of the initial conditions is presented and discussed.
Modeling of an Electromagnetic Vibration Energy Harvester With Motion Magnification
Authors: Li Zhongjie , Brindak Zachary , Zuo Lei
Published: August 2012

This paper presents the modeling and analysis of an electromagnetic harvester for potential applications in large-scale vibration energy harvesting such as from vehicle suspensions or civil structures. The kinematics and dynamics of a motion mechanism and generator are considered, including backlash and friction. In this study, a dynamic model for a rack-pinion type regenerative shock absorber has been derived and analyzed based on differential equations. To understand the influence of the friction and backlash on the system, nonlinear models have been created. Simulations are carried out to study the features of the design. The validation of the models is demonstrated by comparing the simulation results with experimental measurements. Guidelines are given for the design of this type of regenerative shock absorbers.
Heater Size Effect on Temperature Sensing With Wollaston Scanning Thermal Microprobes
Authors: Han Liang , Zhang Yanliang , Borca-Tasciuc Theodorian
Published: August 2012

Scanning thermal microscopy (SThM) is an attractive tool for high spatial resolution thermal characterization with minimal sample preparation1. However, complex thermal contact mechanisms often hinder precise quantification of the sample temperature or thermal properties.2
A Spring-Mass Model of Locomotion With Full Asymptotic Stability
Authors: Shen Zhuohua , Seipel Justin
Published: August 2012

A reduced model of legged locomotion, called the Spring Loaded Inverted Pendulum (SLIP) has previously been developed to predict the dynamics of locomotion. However, due to energy conservation, the SLIP model can only be partially asymptotically stable in the center-of-mass velocity. The more recently developed Clock-Torqued Spring Loaded Inverted Pendulum (CT-SLIP) model is fully asymptotically stable, and has a significantly larger stability basin than SLIP, but requires more than twice as many parameters. To more completely explore the parameter space and understand the reason for improved stability, we develop and analyze a further reduced model called the Forced-Damped Spring Loaded Inverted Pendulum (FD-SLIP) model.
Bloch-Theory-Based Analysis of Damped Phononic Materials
Authors: Frazier Michael J. , Hussein Mahmoud I.
Published: August 2012

In this paper, we combine Bloch theory with familiar techniques of structural dynamics to study the effects of energy dissipation (i.e., damping) in an acoustic metamaterial. The formulation we present has the novel feature of incorporating a temporal component to wave attenuation in addition to the standard spatial component. The frequency band structure reflects the metamaterial response to the damping intensity. In the context of a lumped parameter nested mass model, increasing the magnitude of damping is shown to cause the band structure to descend the frequency range and reveal an intriguing phenomenon: branch overtaking. This effect occurs as dissipation causes the optical branch to descend below the acoustical branch. The resulting decrease in the width of the band gap would impact vibration minimization and isolation. We also examine the effective properties of the metamaterial, specifically, the effective mass and effective stiffness, and the conditions for these quantities to become negative. Finally, the aforementioned material results are shown to be related to their finite counterpart. For ease of exposition, we consider a special form of Rayleigh damping in which the damping is proportional to the stiffness. The intrinsic presence of dissipation in acoustic metamaterials and the limited scientific literature addressing damped wave propagation in periodic media in general motivates our present study.
Polymer Heat Exchangers: An Enabling Technology for Water and Energy Savings
Authors: Cevallos Juan G. , Robinson Frank , Bar-Cohen Avram , Bruck Hugh
Published: August 2012

Polymer heat exchangers (PHXs), using thermally-enhanced composites, constitute a “disruptive” thermal technology that can lead to significant water and energy savings in the thermoelectric energy sector. This paper reviews current trends in electricity generation, water use, and the inextricable relationship between the two trends in order to identify the possible role of PHXs in seawater cooling applications. The use of once-through seawater cooling as a replacement for freshwater recirculating systems is identified as a viable way to reduce the use of freshwater and to increase power plant efficiency. The widespread use of seawater as a coolant can be made possible by the favorable qualities of thermally-enhanced polymer composites: good corrosion resistance, higher thermal conductivities, higher strengths, low embodied energy and good manufacturability. The authors use several seawater cooling case studies to explore the potential water and energy savings made possible by the use of PHX technology. The results from three case studies suggest that heat exchangers made with thermally enhanced polymer composites require less energy input over their lifetime than corrosion resistant metals, which generally have much higher embodied energy than polymers and polymers composites. Also, the use of seawater can significantly reduce the use of freshwater as a coolant, given the inordinate amounts of water required for even a 1MW heat exchanger.
Integrated Management of Energy Storage for Sustainable Operation of Energy Microgrids
Authors: Sharma Ratnesh K. , Kudo Koji
Published: August 2012

Energy microgrids are a key building block of smart grids. Energy microgrids can not only provide voltage and VAR support to the power grid but also reduce the emission footprint of the overall power generation infrastructure. While it provides added advantages like grid decongestion and reduced operating cost for system operators, it creates significant challenges in stable operation and meeting economic goals of the microgrid owners. Currently, energy microgrids are heavily subsidized through government grants/rebates and require high maintenance in terms of skilled operating staff and advance control systems. In this paper, we propose a microgrid energy storage architecture that could reduce the cost of ownership and simplify control and management of energy microgrids while retaining the advantages of reduced emissions and resource consumption. The controls existing in normal energy storage also offers unique opportunities in simplifying the control system of such distributed generation infrastructure and improving the reliability of microgrid in meeting local demand constraints. From a utility operator’s perspective, energy storage provides a reliable and dispatchable source as opposed to intermittent distributed energy resources.
Computational Study on the Bridging Vein Rupture of Blast-Induced Traumatic Brain Injury Using a Numerical Human Head Model
Authors: Wang Chenzhi , Pahk Jae Bum , Balaban Carey D. , Vipperman Jeffrey S.
Published: August 2012

The occurrence of blast-induced traumatic brain injury (bTBI) in people serving in battle environments is dramatically high. The blast front, or leading edge of the shock wave is a brief, acute overpressure wave that travels supersonically with a magnitude that is several times higher than that of ambient. The shock wave propagates through the human head and injures intracranial tissues. Classical neuropathologic signs of bTBI include cerebral contusion, diffuse axonal injury, subdural hematoma (SDH) and subarachnoid hematoma, of which subdural hematoma is the most dominating sign of bTBI. Here, computational finite element (FE) modeling is used to investigate the mechanical process of bTBI. The overall goal of the present study is to find the injury threshold of the SDH injury due to bTBI, by investigating the biomechanical response of the bridging veins in the human brain under shock wave loading that originates from detonation. This research mainly develops a basic FE human head model which consists of skull and parts of the brain. The geometric models of skull and brain are developed from segmentations of magnetic resonance imaging (MRI) files of a real human head. The boundary conditions on the neck and head are modeled as a displacement-fixed condition. The numerically simulated blast waves are applied on the human head model as external loading conditions. The internal response in the subarachnoid space is used as loadings on the bridging vein submodel. The maximum principal stress of the bridging vein is used to determine the whether there is failure of the bridging vein, thus estimating the “injury threshold” of SDH in bTBI. Results show that 150g TNT blast of 1 meter away from the head can result in a high possibility of SDH occurrence.
Optimization of a Centrifugal Fan Impeller Using Kriging Simulated Annealing
Authors: Cadirci Sertac , Selenbas Bugra , Gunes Hasan
Published: August 2012

In this study we present models for the parametric optimization of a centrifugal fan impeller using kriging-simulated annealing (SA) meta-algorithm. First, a kriging model is constructed using a limited number of CFD simulations for the centrifugal fan impeller to be optimized. The inlet and outlet blade angles are chosen to optimize the impeller. A dataset consisting of 22 different blade angles are determined by Latin Hypercube Sampling (LHS). After validation of the kriging model, it is used in conjunction with the simulated annealing and thus a meta-algorithm is developed for the solution of global optimization problem for the impeller optimization. Within the desired range of parameters, it is shown that this meta-algorithm provides a robust, reliable and fast optimization method. The procedures can be used to many problems in engineering. In this study a centrifugal fan impeller is successfully optimized using this procedure.
Design, Manufacturing and Testing of a Camera-Like Aperture Mechanism for a Solar Reactor
Authors: Abdulla Shameel , Zahreddine Hussein , El Zamli Mahmoud , Majid Feras Abdul , Rizk Ihab , Al Hamidi Yasser , Ozalp Nesrin
Published: August 2012

Changes in weather conditions, such as passing clouds, haze, or too sunny etc., result with fluctuation in solar radiation entering a solar reactor. This creates a major problem in solar reactor efficiency. Because: solar reactors must be operated at certain temperatures depending on the required dissociation temperature of the feedstock. For example, natural gas cracking solar reactors require temperatures of about 1500K to produce hydrogen and carbon. Fluctuation in solar radiation due to weather changes creates temperature fluctuation inside the solar reactor preventing from maintaining constant or semi-constant production rate. In this paper, we present our most recent research results toward solving this problem by designing, manufacturing, and testing a camera-like aperture mechanism. With this mechanism, it is possible to achieve semi-constant temperatures inside the solar reactor by adjusting the solar reactor itself against changes in the incoming solar radiation. Results show that when the incoming solar radiation is 5kW, the aperture radius should be 1.8cm to have reactor temperature at 2100K. However, to keep this temperature when the incoming radiation is 7kW, the aperture radius should be 3.2cm. It should be also noted that at lower temperatures, optimum aperture radius converges to one value, which is about 4.7cm.
Enhancement of Vehicle/Roadside Hardware Crash: Dynamic Response of Child Occupant Involved in Vehicle/Pole Impact
Authors: Elmarakbi Ahmed , Krznaric Vid , Sennah Khaled , Altenhof William , Chapman Michael
Published: August 2012

This paper focuses on minimizing child injuries experienced during frontal vehicle-to-pole collisions by improving on the safety and energy absorption of existing traffic pole structures. A finite element computer model, using LS-DYNA software, is used to simulate crash events in order to determine the influence of pole structural and material characteristics on the injury parameters of a hybrid III 3-year-old child dummy occupant. Different pole support systems and laminar traffic poles of different materials are investigated in this paper. It is concluded that the anchored base support and the embedded pole in soil systems provide desirable crashworthy results, thus reducing fatalities and injuries resulting from vehicle impact. It is also recommended to mandate traffic protection devices in all areas with poor energy absorbing characteristics that resemble non-deformable objects.
CFD Simulation of Thermocouple Measurement of Hot Gas Jets
Authors: Etemad Sassan
Published: August 2012

Turbulent convective heat transfer and radiation is simulated for a hot gas jet, impinging perpendicular on a flat surface at 2 jet diameters away from the jet nozzle. A small solid spherical bead, located in the jet centre half way from the wall, represents a thermocouple sensitive point. The bead becomes so hot that it radiates some heat to the colder surrounding surfaces. This phenomenon is responsible for a gap between the jet temperature and the bead temperature. The jet Reynolds number ranged from 7.67*103 to 4.52*104. Bead sizes 1.0 and 2.0 mm are used in jets at 500°C and 900°C. The simulations show that the mentioned temperature differences are significant and grow rapidly with high temperatures but decrease with Reynolds number. The temperature gap, which can be regarded as the thermocouple measurement error, increases also with the bead size. Simulations can be conducted for specific thermocouples with other shapes and materials to assist the measurement process. The modelling methodology is found to be promising for such demanding simulations that require a fine grid for resolving the field near the bead without using excessive cells in the rest of the domain. Hence, further work in this field is envisaged using the same methodology for solving convection, conduction and radiation in one single model and at a reasonable computational cost together with validating measurements. Hopefully this study contributes to a better understanding of the measurement of hot gas jet temperature and its improvement with the aid of simulations.
An Introduction to Systems Engineering
Authors: Hoffman Jay
Published: August 2012

This document describes a graduate course called “An Introduction to Systems Engineering”. The course is being presented as part of a graduate program in the Management of Technology, in response to a specific need. This need has been recognized by technologists, over the years, who have been involved in the broader issues stemming from the mix of technology and business management. It has become clear that these two aspects of day-to-day operations are not always carried off well. However, by training business majors and technologists simultaneously, in some of the same courses of study and in the same class rooms, the management process should become more efficient. The need for exploiting this method is becoming more and more acute, with the passage of time.
Zero D and 3D Analysis of the Centrifugal Compressor of a Gas Turbine and its Evaluation Using Experimental Results
Authors: Karrabi Hadi , Pourfarzaneh H. , Hajilouy-Benisi Ali
Published: August 2012

In compressor design, it is necessary to simulate the compressor before manufacturing and performing experimental studies. One of the most efficient and common modeling methods is zero D analysis using scaling method with constant coefficients. Although it is efficient in the vicinity of the design point, its results are not acceptable in the off design points due to the growing error by getting away from design points. In this research, a novel zero D analysis method is developed predict accurately the compressor performance not only in the design point but also in the off design pint. In this method, variable coefficients are used instead of constant coefficients, which are obtained based on the test results of several compressors. In this paper, the performance characteristics of a gas turbine centrifugal compressor including a radial impeller, a radial diffuser and deswirl vanes are predicted using the zero D approach. Moreover, the 3-D flow field inside the compressor is analyzed using a full 3-D Navier-Stokes code with SST turbulent model. In order to validate the zero D and 3-D analysis results, the existing compressor is investigated experimentally on the operation line of the gas turbine by some experiments in which the flow parameters at the compressor inlet and outlet are measured. Finally, the performance results obtained from 3-D and zero D analysis are compared with the experimental results which show good agreement.