bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Fluid-Structure Interaction
Authors: Gaul Lothar
Published: April 2014

The vibration behavior of ships is noticeably influenced by the surrounding water, which represents a fluid of high density. In this case, the feedback of the fluid pressure onto the structure cannot be neglected and a strong coupling scheme between the fluid domain and the structural domain is necessary. In this work, fast boundary element methods are used to model the semi-infinite fluid domain with the free water surface. Two approaches are compared: A symmetric mixed formulation is applied where a part of the water surface is discretized. The second approach is a formulation with a special half-space fundamental solution, which allows the exact representation of the Dirichlet boundary condition on the free water surface without its discretization. Furthermore, the influence of the compressibility of the water is investigated by comparing the solutions of the Helmholtz and the Laplace equation. The ship itself is modeled with the finite element method. A binary interface to the commercial finite element package ANSYS is used to import the mass matrix and the stiffness matrix. The coupled problems are formulated using Schur complements. To solve the resulting system of equations, a combination of a direct solver for the finite element matrix and a preconditioned GMRES for the overall Schur complement is chosen. The applicability of the approach is demonstrated using a realistic model problem.
Multivariable Control of Vapor Compression Cycle With Transient Heat Flux
Authors: Yang Zehao , Pollock Daniel T. , Wen John T.
Published: April 2014

This paper investigates feedback control of refrigeration cycles for high heat-flux cooling applications, where large transient heat loads may be present. We apply H∞ controller synthesis for disturbance rejection, with the evaporator heat-flux treated as the disturbance input. The controller synthesis is based on model linearization about a chosen operating point. We analyze model uncertainty due to the linearization error to ensure robustness of the closed-loop systems. We use a low-order, lumped-element nonlinear model for the vapor compression cycle. We obtain linearized systems at different operating points, and quantify system nonlinearity using the H∞ norm. Controllers synthesized for the chosen nominal systems are tested for both nominal (near the operating point) and the worst-case performance in nonlinear simulations. For systems close to critical heat-flux (CHF), it is shown that a trade-off exists between the nominal performance and robust stability. For systems far away from CHF, it is shown that the open-loop system has the optimal cooling capacity. The performance of H∞ controller for systems near CHF is validated by experiment.
Modelling of Thermal Rectification in Si and Ge Thin Films
Authors: Chávez-Ángel E. , Sotomayor Torres C. M. , Alzina F.
Published: April 2014

In the present work we have studied an extension of the classical thermal rectification, arising in certain cases from the contact of two dissimilar bulk materials with different temperature dependence of the thermal conductivity, to the Si-Ge system when boundary scattering effects are taken into account. Moreover, the directionality of the in-plane heat flow in a Si plate can be achieved by tuning the thickness and the impurity concentration along the cross section of the plate. We have designed several potential structures with this function in mind and discussed the physics behind.
Set-Based Concurrent Engineering for Preserving Design Bandwidth in Product and Manufacturing System Platforms
Authors: Michaelis Marcel T. , Levandowski Christoffer , Johannesson Hans
Published: April 2014

Assembling products to order or applying straightforward configuration, such as scaling, allow the reuse of ready-designed physical components in high volumes. However, not all companies can exploit economies of scale in this way. They are burdened with additional design work, as requirements on functionality and performance differ among product variants or change over time. Such companies need artifact models and engineering processes that help them manage and develop for variety.

Set-based concurrent engineering has been proposed for dealing with a variety of concepts during development that lead to a single product while storing knowledge gained. This paper adapts this thinking to the preparation and use of product and manufacturing system platforms. Here, the output is not a single product. Rather, a set of design solutions for products and manufacturing systems is designed that delivers flexibility in functionality and performance. In this paper, we call this built-in flexibility design bandwidth.

The paper builds on an integrated artifact model for products and manufacturing systems. The model captures the rationale behind existing designs with their functionality. Here it is combined with principles of set-based concurrent engineering to outline a process for its preparation and use in cases of insufficient bandwidth that require additional designing. The preparation and use are illustrated by applying the model to an example where bandwidth is expanded and preserved.
Extended Exergy as a Locally Significant Environmental Indicator
Authors: Sciubba Enrico
Published: April 2014

The concept of “environmental impact” has evolved to encompass a multi-disciplinary and quite detailed examination of the local and global implications of the interactions of anthropic processes with the biosphere. Sets of quantitative measures of the interaction, called Environmental Indicators (EI), have been proposed with the intent of providing a synthetic, accurate and reliable decision support basis for planners and decision makers. This approach is not devoid of drawbacks: generality conflicts with specificity and it is often difficult to connect a local EI with a more global measure of environmental impact. Furthermore, several of the proposed EIs lack a sound physical basis (in particular, they are not always rigorously rooted on thermodynamics). This paper proposes a method to bridge both gaps by introducing an EI derived strictly from prime thermodynamic concepts (the extended exergy cost, EEC or cee) and by defining a procedure to apply it to local and global scales alike. It is argued that such an EI successfully solves the “externalities” problem for industrial energy conversion systems and that it can also be employed to assess the evolutionary patterns of natural systems. All applications to date demonstrate that cee is indeed a useful tool for the quantification of the primary equivalent resource costs and for their proper internalization in energy systems analyses.
Economic Modeling of Hybrid Energy System
Authors: Bello Olumide , Roberts-Smith Da’Janel , Onyebueke Landon
Published: April 2014

Hybrid Energy Systems (HES) offer hopeful solutions to an array of challenges circumventing conventional energy usage. From sustainable mobility developments to rural communities, hybrid energy systems can provide reliable energy to suffice any load demand when properly sized. Sizing optimality is essential in maintaining low-cost, high-performance and superior efficiency. The methodology for sizing a Photovoltaic-Wind-Diesel with battery backup hybrid energy system and its accompanying costs are calculated using Homer software. The results are presented in this article. Such costs include the concept of levelized cost of energy (LCOE), time-dependent trade-off considerations necessary to deploy a functional, reliable and cost-effective energy system and comfort. The anticipated output of this economic model validates the feasibility of attaining affordability and optimality in a HES that relies on renewable energy and battery storage for applications of varying scales.
Mold Alignment System for Double-Sided Micro Hot Embossing Using Kinematic Constraints
Authors: Conner Glenn , Lek Devanda , Gomez Juan A. , Song In-Hyouk , Park Taehyun , You Byoung Hee
Published: April 2014

A cost effective alignment and positioning system was developed for double-sided hot embossing processes using kinematic principles. Alignment tooling located and transferred the top mold insert location to the proper location for the complementary mold insert and hot embossing was performed. The samples were checked for alignment accuracy and consistency. Adjustments were made and sampling repeated and measured. Results showed the alignment system can improve the locating and positioning of the complementary mold insert in relation to the top in a repeatable and cost effective manner.
A Reduced-Order Model of a Microfluidic Transistor
Authors: Bakarji Joseph , Keniar Khoudor , Cheikh Mohammad , Lakkis Issam
Published: April 2014

A reduced-order model of a Microfluidic Transistor is presented. The transistor is essentially a long micro channel between substrate and a membrane that is pressure actuated. The proposed model captures steady (DC) and small signal (AC) behavior of the device in a manner analogous to standard semiconductor transistor models. The model is based on steady and perturbed unsteady solutions of the conservation of mass and momentum, coupled with an elastic model for the membrane. To improve the accuracy and to enhance the range of validity, the model is enhanced by numerical simulations of the coupled fluid-structure problem. The model predicts dependence of the transconductance on the pressure differentials across the membrane and along the channel. The proposed model also investigates the impact of flow inertia, among other effects, on the dynamic behavior of the transistor.
Design for Multiple Industries: A PDP (Parallel Distributed Processing) Approach
Authors: Fukuda Shuichi
Published: April 2014

A Parallel Distributed Processing (PDP) or Neural Network model is proposed. It restructures our knowledge and experience in product development in the form to achieve widest applicability.

Up to now, product developments have been discussed within one company or one industry at the widest. But in order to increase productivity and to reduce time, cost and energy consumption by a large margin, a great change in our way of thinking is called for. We need to go beyond one company or one industry and team up with other industries.

Just as Concurrent Engineering succeeded in one company or in one industry by bringing downstream information upstream and by processing them concurrently, this goal can be realized if we introduce Parallel Distributed Processing (PDP) model. PDP is more popularly known as Neural Network.

As the relationship between raw materials, intermediate products and final products can be described as a neural network, this goal can be achieved if knowledge and experience are shared across different industries and re-assembled at the intermediate components layer. Then, final products can be developed as the combination of these intermediate components just like Lego.

This not only eliminates overlaps between industries, but this-organizes our knowledge and experience into the form applicable to wider applications and wider areas so that it brings forth greater flexibility in product development.

In short, a PDP or Neural Network model proposed here is the restructuring of our knowledge and experience in order to expand their applications to the widest.

Such restructuring not only achieves widest applicability, but it also helps introduce autonomous distributed economy. Our economy has been too much centralized. If we change our economy system to autonomous distributed system, countries can team up more effectively and develop Win-Win relations, which is most important in this age of globalization.
Numerical Simulation of Aerodynamic Force on Solar Panels
Authors: Giorges Aklilu T. G. , Amador Guillermo J. , Caravati Kevin , Goodman Joseph
Published: April 2014

Significant cost reductions for solar photovoltaic systems can be realized through aerodynamic design improvements for ground mounted and rooftop installations. Current practices in the solar industry are based on ASCE-7 codes created for buildings and do not fully account for wind reduction strategies. Numerical simulation is one of the tools that can be used to evaluate wind loads and improve system designs while maintaining reliability and durability. As a first order analysis, we have numerically simulated a solar photovoltaic panel as a flat plate with an aspect ratio of 0.5, which includes the simulation of turbulence experienced by panels. The flow is simulated using the incompressible Navier-Stokes equation and the turbulent process is simulated using k–ε model. The numerical model and boundary conditions are derived from similar experimental wind tunnel experiments. The aerodynamic force is calculated from the integration of the normal and tangential pressure forces. The result of the numerical simulation shows that the wind load on a solar panel can be successfully simulated numerically and the simulation data can be used to evaluate redesigns of the system, allowing for the effective customization of solar arrays based on local conditions.
Functional Analysis Diagrams With the Representation of Movement Transitions
Authors: Lee Szu-Hung , Jiang Pingfei , Childs Peter R. N. , Gilroy Keith
Published: April 2014

A study on utilising a graphical interface to represent movement transmission within products has been conducted to support a creative conceptual design process that separates the consideration of functional requirements and motion requirements. In engineering design, many representations of product structure have been proposed to assist in understanding how a design is constituted. However, most of these representations demonstrate only functions and are not able to demonstrate design structure. Functional Analysis Diagrams (FAD) provides a solution for this. An FAD shows not only functions but also physical elements by the network of blocks and arrows and thus it is capable of demonstrating various types of information and the design scheme. This characteristic gives FADs an advantage for designers to combine different types of information including useful and harmful interactions to gain an overview of the design task. This study focuses on using circles instead of arrows to represent movement attributes of mechanisms and machine elements in a Kinematic Functional Analysis Diagram (KFAD) and explores methods of utilising it in mechanical design. A commercial case study of medical equipment design conducted with the assistance of KFADs and a component database, mechanism and machine elements taxonomy (MMET), is described to illustrate the process. The design outcome shows that it is feasible to follow the proposed conceptual design process. With the help of KFADs and the machine elements taxonomy to enable consideration of movements, diverse considerations and design solutions are possible.
Nonlinearity in Ultrasonic Guided Waves Propagation in Solids Under Constrained Thermal Expansion
Authors: Nucera Claudio , Lanza di Scalea Francesco
Published: April 2014

Finite strain theory has been employed in the past to mathematically describe nonlinear wave propagation phenomena such as acoustoelasticity (wave speed dependency on quasi-static stress), wave interaction, wave distortion, and higher-harmonic generation. The present work expands the topic of nonlinear wave propagation to the case of a constrained solid subjected to thermal loads. In this framework, the anharmonicity of interatomic potentials, and the absorption of the potential energy corresponding to the (prevented) thermal expansion, are identified as sources of nonlinear effects. Such “residual” energy is, at least, cubic as a function of strain, hence leading to a nonlinear wave equation and higher-harmonic generation. Closed-form solutions are given for the longitudinal wave speed and the second-harmonic nonlinear parameter as a function of interatomic potential parameters and temperature increase. According to the proposed model, the prevented thermal expansion of the solid leads to thermal stresses that, in turn, produce a decrease in longitudinal wave speed and a corresponding increase in nonlinear parameter with increasing temperature. Experimental measurements of the ultrasonic nonlinear parameter on a steel block under constrained thermal expansion confirm this trend. Emphasis is placed on the potential of a nonlinear ultrasonic measurement to quantify thermal stresses from prevented thermal expansion. This knowledge can be extremely useful to prevent thermal buckling of various structures, such as continuous-welded rails in hot weather.
A Simplified Model for the Flow Inside Cascade Impactor
Authors: Nemati Mehr Seyyed Mahdi , Sohrabi Salman , Falsafi Pedram , Gorji Paniz
Published: April 2014

In this paper we developed a new mathematical model for the flow inside cascade impactors and via this simplified model, we determined the particle size distribution by a fast and low cost computational method. Using cascade impactors for determining the particle size distribution, one can use comprehensive CFD methods to fully simulate the particle traces. Although the results from those CFD analyses can be very accurate, usually that is not a time and cost efficient routine. In contrast, we showed that by using our proposed calculation we can estimate the particle size distribution very fast and yet with the slight error — comparing to the results from CFD method.

Cascade impactors are being used to measure the range of substances moving through an opening and determine the particle size of distributed substances. Air flow containing aerosol entering in each stage, after colliding vertically with a plate will deviate 90 degrees from its original direction. Larger (massive) particles cannot follow the flow because of their larger linear momentum. Hence, they will deviate from the flow and deposit on the plate instead. The mass difference before and after the experiment represents the deposited mass in each stage. By integrating multiple uniquely designed stages into one impactor, we can determine size of particles in the flow. Typical cascade impactors consist of up to ten stages in which different size of aerosols are being separated.

This paper presents a simple model for the flow in one single stage of a cascade impactor. Flow inside cascade impactor is approximated by stagnation point potential flow with the stream function of Psi = Axy, and particles are tracked by velocity verlet algorithm. Absorbed particles are associated with unit value; otherwise they are associated with zero. It is assumed that particles in entrance have random size distribution and location. Drag, Saffman and Brownian forces are taken into account in this model for different particle sizes. The results are discussed in detail and compared with data driven from different approaches in the literature.
The Effect of Build Up Edge Formation on the Machining Characteristics in Austempered Ferritic Ductile Iron
Authors: Yazman Şakir , Akdemir Ahmet , Uyaner Mesut , Bakırcıoğlu Barış
Published: April 2014

In this study, chip formation mechanism during the machining of austempered ferritic DI and the effect of the emerging chip morphology on such machining properties as surface roughness and cutting forces has been scrutinized. After austenitizing at 900 °C for 90 min, DI specimens were austempered in a salt bath at 380 °C for 90 min. Chip roots were produced by using a quick stop device during the machining of austempered specimens in different cutting speeds. The metallographies of these specimens were performed and chip morphologies were examined. The fact that the cutting speed increased led to a decrease in built-up edge formation. Depending on this fact, it was detected that the change in built-up edge thickness substantially affected the surface roughness and cutting forces. It was also detected that during the machining, with the effect of cutting forces and stress, spheroidal graphites were broken off in the chip and lost their sphericity and so that the chip became fragile and unstable and grafites here displayed a lubricant feature.
Comprehensive Analyses of Nuclear Safety System Codes
Authors: Roth Glenn A. , Aydogan Fatih
Published: April 2014

Many nuclear system codes have been developed for the main purpose of analyzing reactor performance of a nuclear power plant system during steady state and transient conditions. These codes generally include power plant component models for pumps, pipes, steam generators, pressurizers and other components. The parallel development of these nuclear system codes has been supported by government laboratories, universities, private entities and other organizations throughout the world. This has resulted not only in multiple codes, but multiple versions of the same code with different capabilities. The development paths of each code version have been driven by specific needs. The challenge for the user is to select a code that performs well for the desired analysis problem. Therefore, this work compares different aspects of various nuclear system codes. Firstly, it compares the governing equations for mass, momentum and energy in the evaluated system codes. Secondly, it compares all the codes’ closure models. Closure models are used in system codes to model thermal and mechanical non-equilibrium as well as the coupling of the phases. Thirdly, it compares the Separate Effect Tests (SET) and Integral Effect Tests (IET) employed for the verification and validation (V&V) during the development of each system code. These comparisons cover several thermal and hydraulic models, such as heat transfer coefficients for various flow regimes, two phase pressure correlations, two phase friction correlations, drag coefficients and interfacial models between the fields. Fourthly, major assumptions about the governing and closure equations in these codes are compared and discussed. Fifthly, numerical approach of every code is benchmarked with each other since numerical approach not only affects the speed of the system codes but also the accuracy of the results. Sixthly, the limitations of the codes are evaluated because these codes are challenged by analyzing not only existing nuclear power plants, but also next generation nuclear power plants. The nuclear industry is developing new, innovative reactor designs, such as Small Modular Reactors (SMRs), High-Temperature Gas-cooled Reactors (HTGRs) and others. Sub-types of these reactor designs utilize pebbles, prismatic graphite moderators, helical steam generators, innovative fuel types, and many other design features that may not be fully analyzed by current system codes. The results of this work serve as a guide for development of these system codes and indicate areas where models must be improved to adequately address issues with new reactor design and development activities.
Fatigue Behavior of Pt-20%Ir Coils Used as Implanted Electrodes in Medical Devices
Authors: Zhang Haitao , Li Bernard Q.
Published: April 2014

Pt-20%Ir coils were used in medical devices as conductors for the leads that transfer the electrical signal from an implanted stimulator to the area of the body (e.g., brain or nerves) to be stimulated. In this study, the fatigue behavior and failure mechanism of Pt-20%Ir coils was studied with axial fatigue testing. The stress and strain on the coils was analyzed with the non-linear FEA (finite element analysis) software ABAQUS. A strain vs. fatigue curve was obtained. A SEM (scanning electron microscope) was used to analyze the fatigue fracture surface of the samples.
Thermal Transport to Sessile Droplets on Superhydrophobic Surfaces With Rib and Cavity Features
Authors: Hays R. , Crockett J. , Maynes D. , Webb B. W.
Published: April 2014

This paper reports on measurements of thermal transport to solitary sessile water drops placed on heated superhydrophobic substrates at constant temperature. Data was obtained by heating the surfaces to specified constant temperatures and gently placing a single water droplet of nominally 3 mm diameter on the surface. The droplet was allowed to evaporate completely while two video cameras and one infrared camera imaged it during the evaporation process. The images were post-processed to yield transient geometric and thermal information, including droplet volume, projected droplet-substrate contact area, and droplet temperature. The total evaporation time and Nusselt and Grashof numbers were determined from the measurements. For all scenarios, the substrate temperature was maintained below the saturation temperature of water and was varied from 60 to 100 °C. Three different rib-patterned superhydrophobic substrates were investigated of 0.5, 0.8, and 0.95 cavity fraction, respectively. The rib features ranged in width from 2 to 30 μm and in height from 15 to 20 μm, while the cavities between the ribs ranged in width from 30 to 38 μm. Results were also obtained for a smooth hydrophobic substrate for comparison purposes. Droplet evaporation times increase with substrate cavity fraction and decrease with increasing substrate temperature. Heat transfer rates decrease with increasing substrate cavity fraction and increase with substrate temperature. The Nusselt number generally increases with the Grashof number raised to the 1/4 power, and Nusselt number is larger for lower cavity fraction substrates.
On the Influence of Relative Humidity on the Contact Angle of a Water Droplet on a Silicon Wafer
Authors: Perez-Diaz J. L. , Alvarez-Valenzuela M. A. , Valiente-Blanco I. , Jimenez-Lopez S. , Palacios-Cuesta M. , García O. , Diez-Jimenez E. , Sanchez-García-Casarrubios J. , Cristache C.
Published: April 2014

Contact angle analysis of liquids on surfaces has been extensively used to evaluating solid surface free energy, surface tension, and surface wetting characteristics. Despite the great interest in the contact angle, reported measurements has shown a high variety, which is often related to different contact angle measurement techniques or substrate preparation and oxidation among others. In addition, it is well know, that surface tension and contact angle are modified with temperature. However, no attention has been paid to the influence of the relative humidity (RH) in surface tension or contact angle measurements. In a previous work, we have demonstrated that (for a constant temperature) surface tension on a suspended droplet decreases linearly with RH in the air. In this paper, contact angle of a water droplet on a silicon wafer surface is studied and its relationship with the relative humidity in the air investigated.
Free Vibration of Curvilinearly Stiffened Shallow Shells
Authors: Shi Peng , Kapania Rakesh K.
Published: April 2014

The free vibration of curvilinearly stiffened doubly curved shallow shells is investigated by the Ritz method. Base on the first order shear deformation shell theory and Timoshenko’s 3-D curved beam theory, the strain and kinetic energies of the stiffened shells are introduced. Numerical results with different geometrical shells and boundary conditions, and different stiffener locations and curvatures are analyzed to verify the feasibility of the presented Ritz method for solving the problems. The results show good agreement with those using the FE method.
Effect of the Number of Dental Implant Neck Threads in Contact With the Cortical Bone on Interface Stresses Using Finite Element Method
Authors: Hassan Mohammed Moustafa , El-Wakad Moahamed-Tarek , Bakr E. M.
Published: April 2014

Dental implants are a valuable, safe and predictable solution for patients suffering from tooth loss. The implant shape plays a great role in the success of dental implant, due to its effect on stress distribution in the surrounding bones. Therefore, optimizing some of implant shape parameters may improve stress distribution and consequently may lead to an increase in implant success rate. In this study, the 3D finite element analysis is used to investigate the influence of the number of threads in the neck of the implant on the implant-cortical bone interface stresses. The stress distribution along the implant-bone interface and their displacements were determined using ABAQUS/CAE 6.10 software. Overall, the stress was highest in the cortical bone at the neck of implant and lowest in the cancellous bone regardless of the number of threads in contact with cortical bone. On the other hand, reducing the number of threads in the neck resulted in a decrease in the developed stresses in both types of bones. The developed stresses around the bones decreased gradually in cortical bones and dramatically in cancellous bones when the number of threads decreased in the neck of implant. The stress reduction between the smooth neck to the fully threaded neck decreased the developed stresses by 24% in the cortical bone. However, due to improve the implant osseointegration, it is recommended to keep one or two threads in the cortical bone.
Value-Centric Approaches to Design, Operations, and Maintenance of Wind Turbines
Authors: Khadabadi Madhur A. , Marais Karen B.
Published: April 2014

Wind turbine maintenance is emerging as an unexpectedly high component of turbine operating cost and there is an increasing interest in managing this cost. Here, we present an alternative view of maintenance as a value-driver, and develop an optimization algorithm to maximize the value delivered by maintenance. We model the stochastic deterioration of the turbine in two dimensions: the deterioration rate, and the extent of deterioration, and view maintenance as an operator that moves the turbine to an improved state in which it can generate more power and so earn more revenue. We then use a standard net present value (NPV) approach to calculate the value of the turbine by deducting the costs incurred in the installation, operations and maintenance from the revenue due to the power generation. The application of our model is demonstrated using several scenarios with a focus on blade deterioration. We evaluate the value delivered by implementing blade condition monitoring systems (CMS). A higher fidelity CMS allows the blade state to be determined with higher precision. With this improved state information, an optimal maintenance strategy can be derived. The difference between the value of the turbine with and without CMS can be interpreted as the value of the CMS. The results indicate that a higher fidelity (and more expensive) condition monitoring system (CMS) does not necessarily yield the highest value, and, that there is an optimal level of fidelity that results in maximum value. The contributions of this work are twofold. First, it is a practical approach to wind turbine valuation and operation that takes operating and market conditions into account. This work should therefore be useful to wind farm operators and investors. Second, it shows how the value of a CMS can be explicitly assessed. This work should therefore be useful to CMS manufacturers and wind farm operators.
Mechanical Characterization of Healable Cross-Ply Composites
Authors: Nielsen Christian , Nemat-Nasser Sia
Published: April 2014

Polymers with thermally-reversible Diels-Alder cross-links have been previously shown to heal cracks and regain structural integrity. Complete recovery of fracture toughness has been experimentally observed in neat samples under ideal conditions. In the present work, new healable polymer samples containing glass or carbon reinforcing fibers in [90,0]s cross-ply orientations are fabricated and characterized using dynamic mechanical analysis (DMA). The DMA results are compared with one-dimensional composite and beam analyses. Transverse cracks observed in microscopy images and attributed to residual thermal stresses are considered using a shear lag method. Crack healing is assumed to be occurring as a function of the sample temperature, where the limits of healing are established by other experiments. By considering the composite constituent properties, sample geometries, and the presence of cracks that heal during the test, the DMA measurements are accurately modeled.
Nucleate Pool Boiling Enhancement Experiments for Heat Transfer Laboratory
Authors: Dikici Birce , Eno Edidiong , Compere Marc
Published: April 2014

Boiling heat transfer is used in variety of industrial processes and applications, such as refrigeration, vapor cycle power generation, heat exchangers, petroleum refining, and chemical manufacturing. It is also used in cooling of high power electronic components, nuclear reactor cooling and seawater desalination. Enhancements in boiling heat transfer processes are critical for making these applications more energy efficient.

The aim of this paper is to demonstrate the water pool boiling phenomena under the influence of surfactant additives. The test setup has multiple benefits. First, the test setup enhances teaching in Heat Transfer, Transport Phenomena, Fluid Mechanics, and Renewable Energy through in class demonstrations and student experiments. Second, the test setup provides a platform for research in boiling enhancement. This apparatus will be used in the classroom for hands-on experiments and also as a diagnostic tool for boiling performance improvement methods like surfactant effects. For determining surfactant effects, different concentrations of sodium lauryl sulfate (SLS) added to pure water were tested and enhancement through surfactant is quantified.

With the integration of boiling experiments into coursework, mechanical engineering students will develop laboratory experiences to enhance the learning of basic boiling concepts. Three pool boiling projects that can be integrated into heat transfer laboratory are explained. The suggested test setup is a valuable tool for improving teaching effectiveness in both classroom and laboratory of heat transfer related classes.
System Identification and Observer-Based Control Design of a Piezoelectric Actuated Cantilever Beam
Authors: Lu Bei , Li Qifu
Published: April 2014

Cantilever beams are widely found in many different applications such as aircraft wings and microelectromechanical devices. One of the problems associated with cantilever structures is that uncontrolled tip vibrations can cause serious structural damage. This paper presents one possible solution to control the oscillation of a cantilever beam. The solution involves the use of strain gauges to measure the oscillation and piezoelectric actuators to control the tip deflection. The piezoelectric cantilever beam is modeled as a second-order system with one degree-of-freedom. The system parameters, including the natural frequency, the damping ratio, and the zeros, are identified from measurement of free and sinusoidal responses. An observer-based controller is then designed using the identified dynamics model. Simulation and experimental results demonstrate the accuracy of the model and the performance of the controller.
Safety of Fitness Equipment Cables
Authors: Barnett Ralph L.
Published: April 2014

There is a family of fitness machines that provides a manual workout task requiring the user to push or pull against a resistance provided by a stack of weight plates. The weight system is usually linked with a single cable to a gripping or user interface device to produce a constant resistance. A fracture of the tensioned cable along its length or at its end connectors causes a sudden acceleration of the grip or other interface device driven by the operator’s push or pull. The sudden loss of resistance often results in an exerciser pulling a heavy bar into his or her face. Because falling weights, accelerating grips and rapidly unloading muscles are all hazardous, manufacturers of exercise machines want to maintain the structural integrity of the cables. To accomplish this, manufacturers usually recommend “scheduled servicing” of their cables. This Preventive Maintenance (PM) strategy is frustrated by nylon sheathing that hides the cable failures. Further, the swedged or silver soldered connectors often fail covertly by internal fatigue fractures. A more effective PM strategy has been adopted by many manufacturers called “Scheduled Replacement”; they advocate annual cable replacement. Here the nemeses are sloth and greed, best expressed by the philosophy, “if it ain’t broke, don’t fix it.” As a first consideration of fault tolerant design, a redundant duplication of the cable system was added to a fitness machine; this is called “active redundancy.” This paper demonstrates the inadequacy of active redundancy for eliminating the catastrophic failure mode. Instead, the adoption of a “dormant/standby” redundancy is shown to provide the requisite safety. The proposed system not only eliminates the “fail-to-danger” mode, it provides the most economical use of the cable in the sense that it never discards a cable until its life is exhausted.
Effects of Turbulent Blood Flow on Abdominal Aortic Aneurysms: A Fluid-Structure Interaction Study
Authors: Lin Shengmao , Gu Linxia
Published: April 2014

Abdominal aortic aneurysm (AAA), local dilations of the infrarenal aorta, is the 13th leading cause of mortality in US. Various tools have been used to investigate the effect of blood flow on the mechanics of AAA, which might predict its fracture potential, a life-threaten event. The modeling techniques are gaining popularity, including the partially or fully coupled fluid-structure interaction method (p-FSI and f-FSI, respectively) and the static computational solid stress (CSS) analyses. In the present study, comparison among the above mentioned three computational methods were performed to identify the effective means to characterize the effects of pulsatile turbulent blood flow on predicting the stress distribution on AAA. Results have shown that ignorance of blood flow in simulation will underestimate the wall stress calculation and the flexibility of aneurysm wall has a large impact in simulating the blood through the AAA.
Experimental Study of the Characteristics of Gas Impinging Streams Using PIV Technique
Authors: Wei Wei , Li ZhiYi , Liu Fengxia , Liu Zhijun
Published: April 2014

Impinging streams technology has been widely used in many applications in recent years because of its enhancement to the heat and mass transfer between phases. In this paper, in order to investigate the influences of the impinging distance and flow rate on the characters of the flow field, gas-gas impinging streams flow fields are tested experimentally and analyze qualitatively with particle image velocimetry (PIV). The experimental equipment consists of two opposite nozzles which are the same axis. A PIV system is used to measure the characters of the 2-D flow field between two opposite nozzles. The gas is delivered by a compressor through two opposite jets which could be seeded with oil droplets as tracer particles. The effects of the flow rate and impinging distance on the velocity fields of impinging zone are investigated in detail. As the flow rate increases from 0.2 m3/h to 0.8 m3/h, the width of impinging zone increases from 0.25 to 0.5. However, the range of impinging zone does not change significantly as the impinging distance increases from 61mm to 94mm. The results indicate that the PIV technique is an effective method to measure and analyze the characters of impinging streams.
Experimental Study of Swirling Jets and Axial Forcing on Round Jets
Authors: McCleney Amy B. , Bardet Philippe M.
Published: April 2014

In jets, swirl can significantly enhance growth and mixing. This can lead to better chemical process efficiencies, increased combustion completeness, lower exhaust plume temperatures, and reduction in pollutant by-products. Exciting natural instabilities can enhance mixing further. Past research on forcing of swirling jets resulted in limited change in flow behavior. This could be attributed to either low Reynolds numbers or imposed modes that were solely axial or azimuthal. In our experiment, both round and free swirling jets are created by independently controlling the axial and azimuthal momentum injection rates; the resulting water stream discharges into a large tank. Axial forcing on a round jet is varied for Strouhal number ranging from 0 to 0.45 and Reynolds number, Re, of 5,700 for small amplitudes. An unforced swirling jet is also presented for Re of 1,100 and 5,800 with a Swirl of 0.05. While the highest Reynolds number studied here is relevant to industrial applications, there is a dearth of experimental data in this range. Flow structures in the shear layer are identified with PLIF. Fluorescent dye is injected uniformly in the circumference of the boundary layer; this allows visualizing the effect of forcing and swirl on the shear layer in the near and far field. The results offer insight into controlling the spacing of the vortex rings formed by axial forcing.
Response of Post-Mortem Human Head Under Primary Blast Loading Conditions: Effect of Blast Overpressures
Authors: Ganpule Shailesh , Salzar Robert , Chandra Namas
Published: April 2014

Blast induced neurotrauma (BINT), and posttraumatic stress disorder (PTSD) are identified as the “signature injuries” of recent conflicts in Iraq and Afghanistan. The occurrence of mild to moderate traumatic brain injury (TBI) in blasts is controversial in the medical and scientific communities because the manifesting symptoms occur without visible injuries. Whether the primary blast waves alone can cause TBI is still an open question, and this work is aimed to address this issue. We hypothesize that if a significant level of intracranial pressure (ICP) pulse occurs within the brain parenchyma when the head is subjected to pure primary blast, then blast induced TBI is likely to occur.

In order to test this hypothesis, three post mortem human heads are subjected to simulated primary blast loading conditions of varying intensities (70 kPa, 140 kPa and 200 kPa) at the Trauma Mechanics Research Facility (TMRF), University of Nebraska-Lincoln. The specimens are placed inside the 711 mm × 711 mm square shock tube at a section where known profiles of incident primary blast (Friedlander waveform in this case) are obtained. These profiles correspond to specific field conditions (explosive strength and stand-off distance). The specimen is filled with a brain simulant prior to experiments. ICPs, surface pressures, and surface strains are measured at 11 different locations on each post mortem human head. A total of 27 experiments are included in the analysis.

Experimental results show that significant levels of ICP occur throughout the brain simulant. The maximum peak ICP is measured at the coup site (nearest to the blast) and gradually decreases towards the countercoup site. When the incident blast intensity is increased, there is a statistically significant increase in the peak ICP and total impulse (p<0.05). Even after five decades of research, the brain injury threshold values for blunt impact cases are based on limited experiments and extensive numerical simulations; these are still evolving for sports-related concussion injuries. Ward in 1980 suggested that no brain injury will occur when the ICP<173 kPa, moderate to severe injury will occur when 173 kPa<ICP<235 kPa and severe injury will occur when ICP>235 kPa for blunt impacts. Based on these criteria, no injury will occur at incident blast overpressure level of 70 kPa, moderate to severe injuries will occur at 140 kPa and severe head injury will occur at the incident blast overpressure intensity of 200 kPa. However, more work is needed to confirm this finding since peak ICP alone may not be sufficient to predict the injury outcome.
Influence of Engine Harmonics on Synchroniser Mechanism Dynamics
Authors: Walker Paul D. , Zhang Nong
Published: April 2014

Synchronizer mechanisms play an important role in the selection and engagement of gears in manual, automated manual and dual clutch transmissions (DCT). These mechanisms rely heavily on the balancing of torque loads in cone clutches, dog gears and from losses in the gearbox to ensure repeatable and reliable actuation, with excessive wear on friction and contact surfaces leading to degradation of actuation and potential mechanism failure. Dual clutch transmissions, in particular, provide a unique operating environment for synchronizers, most notably is its actuation with the engine still driving the wheels during normal driving conditions. Thus, the consideration of increased transmitted vibrations through the powertrain must be evaluated to study the impact of these vibrations on the synchronizer.

To conduct this investigation this paper develops a detailed multi-body dynamic model of a typical automotive powertrain equipped with a dual clutch transmission. This includes engine models with torque harmonics that capture the instantaneous torque variations from piston firing in the engine. As the main consideration of this paper is the influence of engine harmonics, the semi-definite powertrain model is simplified to a fixed-free system and the response of the synchronizer mechanism to harmonic torque inputs is analyzed.

Parametric analysis of the system is conducted to analyze the influence of variables — including gear ratio, torsional damper, system damping, and engine configuration — on the dynamic response of the mechanism. Results demonstrate the influence of each of these variables on synchronizer dynamics in the steady state, with stiffness of torsional damper having the strongest influence on forced vibration. Additionally, results vary significantly between single and dual lay-shaft transmissions.
A Numerical Investigation of the Fluid Flow in a Chandler Loop for Thrombus Studies
Authors: Touma Hisham , Sahin Iskender , Gaamangwe Tidimogo , Gorbet Maud B. , Peterson Sean D.
Published: April 2014

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a stress field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For very low rotation rates, the stress field can be approximated using laminar flow in a straight tube as a model. However, as the rotation rate increases, while still maintaining laminar flow, the effect of the tube curvature causes the stress field to deviate considerably from the straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing non-dimensional fluid dynamic parameters. We find that the Dean number, which is proportional to the rotation rate, is the dominant parameter in determining the fluid strain rate. We propose an empirical formula for predicting the average fluid strain rate magnitude in the working fluid that is valid over a wide parameter space to be used in lieu of the common, yet restrictive, straight tube-based prediction.