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Full-Text Articles in Mechanical Engineering

Feasibility Of Attaining Fully Equiaxed Microstructure Through Process Variable Control For Additive Manufacturing Of Ti-6al-4v, Sarah Louise Kuntz Jan 2016

Feasibility Of Attaining Fully Equiaxed Microstructure Through Process Variable Control For Additive Manufacturing Of Ti-6al-4v, Sarah Louise Kuntz

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One of the greatest challenges in additive manufacturing is fabricating titanium structures with consistent and desirable microstructure. To date, fully columnar deposits have been achieved through direct control of process variables. However, the introduction of external factors appears necessary to achieve fully equiaxed grain morphology using existing commercial processes. This work introduces and employs an analytic model to relate process variables to solidification thermal conditions and expected beta grain morphology at the surface of and at the deepest point in the melt pool. The latter is required in order to ensure the deposited microstructure is maintained even after the deposition …


Vehicle Level Transient Aircraft Thermal Management Modeling And Simulation, Adam Donovan Jan 2016

Vehicle Level Transient Aircraft Thermal Management Modeling And Simulation, Adam Donovan

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Many advances in technology are expected to increase the capabilities of next generation aircraft, and these advances will increase the thermal load on the aircraft as well. In order to assess and account for these increased thermal loads, three studies were performed: a fuel pump trade study, a high energy pulsed system (HEPS) implementation study, and a legacy vehicle environmental control system (ECS) study. The fuel pump study addresses the effect of the implementation of a centrifugal fuel pump versus a variable displacement fuel pump. Traditionally, aircraft designers have used a centrifugal fuel pump over a piston based pump based …


Silver Nanoparticles Supported On Carbon Nanotube Carpets: Influence Of Surface Functionalization, Anil K. Karumuri, Dhawal P. Oswal, Heather A. Hostetler, Sharmila M. Mukhopadhyay Jan 2016

Silver Nanoparticles Supported On Carbon Nanotube Carpets: Influence Of Surface Functionalization, Anil K. Karumuri, Dhawal P. Oswal, Heather A. Hostetler, Sharmila M. Mukhopadhyay

Mechanical and Materials Engineering Faculty Publications

The effectiveness of nanoparticle-based functional devices depends strongly on the surface morphology and area of the support. An emerging powerful approach of increasing the available surface area without decreasing strength or increasing bulk is to attach arrays of suitable nanotubes on the surface, and to attach the necessary nanoparticles to them. Earlier publications by this team have shown that carpet-like arrays of carbon nanotubes (CNTs) can be successfully grown on a variety of larger carbon substrates such as graphite, foams and fabric, which offer hierarchical multiscale supporting architecture suitable for the attachment of silver nanoparticles (AgNPs). A limiting factor of …


Locally Optimized Covariance Kriging For Non-Stationary System Responses, Daniel Lee Clark Jr. Jan 2016

Locally Optimized Covariance Kriging For Non-Stationary System Responses, Daniel Lee Clark Jr.

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In this thesis, the Locally-Optimized Covariance (LOC) Kriging method is developed. This method represents a flexible surrogate modeling approach for approximating a non-stationary Kriging covariance structures for deterministic responses. The non-stationary covariance structure is approximated by aggregating multiple stationary localities. The aforementioned localities are determined to be statistically significant utilizing the Non-Stationary Identification Test. This methodology is applied to various demonstration problems including simple one and two-dimensional analytical cases, a deterministic fatigue and creep life model, and a five-dimensional fluid-structural interaction problem. The practical significance of LOC-Kriging is discussed in detail and is directly compared to stationary Kriging considering computational …


Transient Analysis Of A Solid Oxide Fuel Cell/ Gas Turbine Hybrid System For Distributed Electric Propulsion, Venkata Adithya Chakravarthula Jan 2016

Transient Analysis Of A Solid Oxide Fuel Cell/ Gas Turbine Hybrid System For Distributed Electric Propulsion, Venkata Adithya Chakravarthula

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Gas turbine technology for aerospace applications are approaching limits in efficiency gains as increases in efficiency today occurs in very small increments. One limitation in conventional gas turbine technology is the combustion process, which destroys most of the exergy in the cycle. To address this limitation in a traditional Brayton power cycle, a hybrid system which is integrated with Solid Oxide Fuel Cell (SOFC) and gas turbine is developed. Hybrid systems involving fuel cells have better efficiencies than conventional power generation systems. Power generation systems with improved performance from low fuel utilizations and low maintenance costs are possible. The combination …


Aircraft Thermal Management Using Liquefied Natural Gas, Sean Robert Nuzum Jan 2016

Aircraft Thermal Management Using Liquefied Natural Gas, Sean Robert Nuzum

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Many technological advances are expected to increase the capabilities of the future aircraft, both civilian and military. These improvements come in many forms such as new wing or fuselage shapes to improve lift or decrease drag. Other improvements are internal. One of these areas is the inclusion of advanced electronic systems for various roles. These changes affect a wide range of aircraft systems including, but not limited to avionics, power generation and thermal management. While these modifications promise to increase aircraft capabilities such as its range, payload or other key performance parameters, there are some significant drawbacks. One drawback is …


Hybrid Particle Image Velocimetry With The Combination Of Cross-Correlation And Optical Flow Method, Mark Bradley Johnson Jan 2016

Hybrid Particle Image Velocimetry With The Combination Of Cross-Correlation And Optical Flow Method, Mark Bradley Johnson

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Particle Image Velocimetry (PIV) has been of relevant discussions lately as the equipment used to obtain temporally and spatially resolved flow fields have advanced rapidly. Despite these advancements, the accuracy of evaluating these images have yet to exceed expectations. Current techniques typically utilize one method, either correlation based (frequently) or optical flow (non-frequently), and both are vulnerable to specific conditions incorporated in the PIV images. Only through the combination of two methods, cross correlation and optical flow, can a technique benefit from the strengths of each method while concealing the flaws each individual method contains. The Hybrid Particle Image Velocimetry …


An Adapted Approach To Process Mapping Across Alloy Systems And Additive Manufacturing Processes, Luke Charles Sheridan Jan 2016

An Adapted Approach To Process Mapping Across Alloy Systems And Additive Manufacturing Processes, Luke Charles Sheridan

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The continually growing market for metal components fabricated using additive manufacturing (AM) processes has called for a greater understanding of the effects of process variables on the melt pool geometry and microstructure in manufactured components for various alloy systems. Process Mapping is a general approach that traces the influence of process parameters to thermal behavior and feature development during AM processing. Previous work has focused mainly on Ti-6Al-4V (Ti64), but this work uses novel mathematical derivations and adapted process mapping methodologies to construct new geometric, thermal, and microstructural process maps for Ti64 and two nickel superalloy material systems. This work …


Inlet Distortion Effects On The Unsteady Aerodynamics Of A Transonic Fan Stage, Daniel Oliver Reilly Jan 2016

Inlet Distortion Effects On The Unsteady Aerodynamics Of A Transonic Fan Stage, Daniel Oliver Reilly

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A computational study was conducted to understand the influence of aircraft inlet distortion flow on the unsteady aerodynamic loading of a gas turbine fan stage. A single stage, transonic fan design with no inlet guide vanes was modeled with a commercial, computational fluid dynamics solver, STAR-CCM+, using the harmonic balance technique. The baseline inlet boundary condition applied to the model is consistent with that of a homeomorphic variant of the M2129 S-duct, and exhibited stagnation pressure distortion and a swirl pattern. The baseline inlet flow was decomposed and parameterized into a set of inlet boundary conditions which were individually applied …


The Effect Of Laser Power And Scan Speed On Melt Pool Characteristics Of Pure Titanium And Ti-6al-4v Alloy For Selective Laser Melting, Chandrakanth Kusuma Jan 2016

The Effect Of Laser Power And Scan Speed On Melt Pool Characteristics Of Pure Titanium And Ti-6al-4v Alloy For Selective Laser Melting, Chandrakanth Kusuma

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Selective Laser Melting (SLM) is an additive manufacturing (AM) technique that creates complex parts by selectively melting metal powder layer-by-layer. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy are melted on a substrate of the same material as powder using an in-house built SLM machine. Multiple combinations of laser power and scan speed are used for single bead fabrication while the laser beam diameter and powder layer thickness are kept constant. This experimental study investigates the influence of laser power, scan speed and …


The Effects Of Micro-Dimple Texture On The Friction And Thermal Behavior Of A Point Contact, Utsav Kamleshbhai Parmar Jan 2016

The Effects Of Micro-Dimple Texture On The Friction And Thermal Behavior Of A Point Contact, Utsav Kamleshbhai Parmar

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This study investigates the effects of the micro-dimple texture on the friction and surface temperature performances of a ball-on-disk contact, operating under the speed and load ranges that cover typical gearing applications. Circular shaped micro-dimple arrays with different dimple center distances and dimple depths are implemented on the ball surface to quantify the impacts of these two parameters on the friction coefficient and the maximum ball surface temperature. In addition, the contacts of three surface texture combinations, namely micro-dimpled and polished ball surface versus polished disk surface, polished ball surface versus polished disk surface and ground ball surface versus ground …


Elucidating The Role Of Microstructure, Texture, And Microtexture On The Dwell Fatigue Response Of Ti-6al-4v, Alec Mitchell Blankenship Jan 2016

Elucidating The Role Of Microstructure, Texture, And Microtexture On The Dwell Fatigue Response Of Ti-6al-4v, Alec Mitchell Blankenship

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Ambient temperature dwell sensitivity is known to be deleterious to the fatigue response of near-alpha titanium alloys. Dwell fatigue refers to the presence of a sustained hold at peak stress as opposed to the continuous variation of normal cyclic fatigue loading. This reduction in failure life-times from dwell loading is attributed to early crack nucleation and faster crack propagation. The degradation is the result of plastic anisotropy on the microstructural scale along with tendency of titanium alloys to creep at low temperatures at stresses well below the 0.2% offset yield strength. Despite being the most widely used titanium alloy, Ti-6Al-4V …


On The Experimental Evaluation Of Loss Production And Reduction In A Highly Loaded Low Pressure Turbine Cascade, Philip Steven Bear Jan 2016

On The Experimental Evaluation Of Loss Production And Reduction In A Highly Loaded Low Pressure Turbine Cascade, Philip Steven Bear

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Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with …


The Effect Of A Reversible Shear Transformation On Plastic Deformation Of An Amorphous Solid, Nikolai V. Priezjev Sep 2015

The Effect Of A Reversible Shear Transformation On Plastic Deformation Of An Amorphous Solid, Nikolai V. Priezjev

Mechanical and Materials Engineering Faculty Publications

Molecular dynamics simulations are performed to investigate the plastic response of a model glass to a local shear transformation in a quiescent system. The deformation of the material is induced by a spherical inclusion that is gradually strained into an ellipsoid of the same volume and then reverted back into the sphere. We show that the number of cage-breaking events increases with increasing strain amplitude of the shear transformation. The results of numerical simulations indicate that the density of cage jumps is larger in the cases of weak damping or slow shear transformation. Remarkably, we also found that, for a …


Diffusion Of A Janus Nanoparticle In An Explicit Solvent: A Molecular Dynamics Simulation Study, Ali Kharazmi, Nikolai V. Priezjev Jun 2015

Diffusion Of A Janus Nanoparticle In An Explicit Solvent: A Molecular Dynamics Simulation Study, Ali Kharazmi, Nikolai V. Priezjev

Mechanical and Materials Engineering Faculty Publications

Molecular dynamics simulations are carried out to study the translational and rotational diffusion of a single Janus particle immersed in a dense Lennard-Jones fluid. We consider a spherical particle with two hemispheres of different wettabilities. The analysis of the particle dynamics is based on the time-dependent orientation tensor, particle displacement, as well as the translational and angular velocity autocorrelation functions. It was found that both translational and rotational diffusion coefficients increase with decreasing surface energy at the nonwetting hemisphere, provided that the wettability of the other hemisphere remains unchanged. We also observed that in contrast to homogeneous particles, the nonwetting …


Plastic Deformation Of A Model Glass Induced By A Local Shear Transformation, Nikolai V. Priezjev Mar 2015

Plastic Deformation Of A Model Glass Induced By A Local Shear Transformation, Nikolai V. Priezjev

Mechanical and Materials Engineering Faculty Publications

The effect of a local shear transformation on plastic deformation of a three-dimensional amorphous solid is studied using molecular dynamics simulations. We consider a spherical inclusion, which is gradually transformed into an ellipsoid of the same volume and then converted back into the sphere. It is shown that at sufficiently large strain amplitudes, the deformation of the material involves localized plastic events that are identified based on the relative displacement of atoms before and after the shear transformation. We find that the density profiles of cage jumps decay away from the inclusion, which correlates well with the radial dependence of …


Computational Fluid Dynamics Simulation Of Intracranial Aneurysms - Comparing Size And Shape, Zifeng Yang, Hongtao Yu, George P. Huang, Ryan Schwieterman, Bryan Ludwig Feb 2015

Computational Fluid Dynamics Simulation Of Intracranial Aneurysms - Comparing Size And Shape, Zifeng Yang, Hongtao Yu, George P. Huang, Ryan Schwieterman, Bryan Ludwig

Mechanical and Materials Engineering Faculty Publications

Objective: To study the hemodynamics of an anatomic internal carotid artery aneurysm derived from a patient-specific model and then manipulate into two phantom morphologies: one growing uniformly by size and the other changing shape unevenly. Methods: The computational model of the saccular, internal carotid artery, aneurysm was constructed from 3D rotational, digitally subtracted, catheter angiography images. Computational fluid dynamics simulations were performed under pulsatile cardiac flow conditions. Velocity vectors, streamlines, pressure, and wall shear stress (WSS) and its variance distributions were quantitatively visualized. Results: The maximum pressure and WSS from the time-averaged distribution on the inside saccular surface of the …


Multifunctional Nanomaterials For Biomedical Engineering: Unique Properties, Fabrications, And Diverse Applications, Jen-Jie Chieh, Sharmila M. Mukhopadhyay, Yali Cui Jan 2015

Multifunctional Nanomaterials For Biomedical Engineering: Unique Properties, Fabrications, And Diverse Applications, Jen-Jie Chieh, Sharmila M. Mukhopadhyay, Yali Cui

Mechanical and Materials Engineering Faculty Publications

Nanomaterials possess many unique properties useful for biomedical applications ranging from preoperative and intraoperative imaging to coatings, assays, and cell scaffolds. Their popularity and production value are full of competitiveness. Their related methodologies and instruments are also created or emphasized as the mainstream. Since multifunctional nanomaterials attract interests and attention of researchers, engineers, and businessmen in biomedical engineering, this journal is set up to publish a special issue devoted to this topic. The result is a collection of five original research articles, whose authors belong to academic or research institutions of five different countries from Asia, Europe, and America. Papers …


Finite Element Analysis Of System-Level Electronic Packages For Space Applications, Adrien Lambert, Ahsan Mian, Justin Hogan, Todd Kaiser, Brock Lameres Jan 2015

Finite Element Analysis Of System-Level Electronic Packages For Space Applications, Adrien Lambert, Ahsan Mian, Justin Hogan, Todd Kaiser, Brock Lameres

Mechanical and Materials Engineering Faculty Publications

Thermal analysis was required in order to aid in the design and testing of a radiation tolerant computing (RTC) system using a radiation sensor. During development of the system, different test beds were employed in order to characterize the radiation sensor and its supporting electronic systems. The most common preliminary tests are high altitude balloon tests which allow the sensor to experience cosmic radiation at high altitudes, consistent with space flight operations. In this study, finite element analysis (FEA) was used to evaluate primary system architecture, system support structures, and the flight payload in order to determine if the system …


An Experimental Investigation On Friction And Scuffing Failure Of Lubricated Point Contacts, Sai Goutham Soma Jan 2015

An Experimental Investigation On Friction And Scuffing Failure Of Lubricated Point Contacts, Sai Goutham Soma

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Scuffing failure is a catastrophic thermal failure mode induced by the extreme surface temperature of the contacting components. As two mechanical elements roll against each other with high sliding motion, the frictional heat flux elevates the surface temperature to exceed the critical limit, resulting in the welding of the surfaces. The relative motion then tears the welded surfaces apart, causing the damage. Scuffing failure has been an important failure mode for rolling machine elements such as bearings and gears in aerospace applications, owing to the very high operating speeds. Recently, this failure mode has extended to the automotive field, where …


A Distributed Surrogate Methodology For Inverse Most Probable Point Searches In Reliability Based Design Optimization, James Davidson Jan 2015

A Distributed Surrogate Methodology For Inverse Most Probable Point Searches In Reliability Based Design Optimization, James Davidson

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Surrogate models are commonly used in place of prohibitively expensive computational models to drive iterative procedures necessary for engineering design and analysis such as global optimization. Additionally, surrogate modeling has been applied to reliability based design optimization which constrains designs to those which provide a satisfactory reliability against failure considering system parameter uncertainties. Through surrogate modeling the analysis time is significantly reduced when the total number of evaluated samples upon which the final model is built is less than the number which would have otherwise been required using the expensive model directly with the analysis algorithm. Too few samples will …


High Temperature Transient Creep Analysis Of Metals, Sara Mirmasoudi Jan 2015

High Temperature Transient Creep Analysis Of Metals, Sara Mirmasoudi

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The ability to design vehicles capable of reaching hypersonic speeds has become a necessity to satisfy industry requirements, hence requiring the need for better understanding of creep behavior of materials. Although the steady state creep of metals has been analyzed rigorously, there is little known about transient creep of many metals. Understanding transient creep behavior of metals is crucial in analysis and design of short term hypersonic flight applications. Hence, a transient creep analysis of 304SS, Al7075-T6, Al2024-T6, Inconel 625, Inconel 718, and Rene N4 is carried out focusing on the microstructural behavior of these metals undergoing high temperature operating …


Surface Treatments To Tailor The Wettability Of Carbon Nanotube Arrays, Lvmeng He Jan 2015

Surface Treatments To Tailor The Wettability Of Carbon Nanotube Arrays, Lvmeng He

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Carbon nanotubes (CNTs) have gained great attention due to their excellent mechanical, electrical, and thermal properties. Carbon nanotube (CNT) arrays attached to solid substrates resemble a nano-carpet and have potentials in a variety of devices. In this study, the focus is to investigate the surface modification approaches of CNT carpets on flat (compressed) graphite. Wettability, or permeation of a liquid such as water into the CNT strands, may play very significant roles in many applications where a CNT-coated device may be used in aqueous environment. Short-term microwave plasma treatments were used in this project to functionalize CNT carpets for wettability. …


Dynamical Heterogeneity In Periodically Deformed Polymer Glasses, Nikolai V. Priezjev Jan 2014

Dynamical Heterogeneity In Periodically Deformed Polymer Glasses, Nikolai V. Priezjev

Mechanical and Materials Engineering Faculty Publications

The dynamics of structural relaxation in a model polymer glass subject to spatially homogeneous, time-periodic shear deformation is investigated using molecular dynamics simulations. We study a coarse-grained bead-spring model of short polymer chains below the glass transition temperature. It is found that at small strain amplitudes, the segmental dynamics is nearly reversible over about 104 cycles, while at strain amplitudes above a few percent, polymer chains become fully relaxed after a hundred cycles. At the critical strain amplitude, the transition from slow to fast relaxation dynamics is associated with the largest number of dynamically correlated monomers as indicated by the …


Variable Speed Flapping Wing Micro Air Vehicle Using A Continuous Variable Transmission Design, Jason C. Chuang Jan 2014

Variable Speed Flapping Wing Micro Air Vehicle Using A Continuous Variable Transmission Design, Jason C. Chuang

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Flapping wing micro air vehicles (FWMAV) have very unique flight mechanics in two-wing orientation. Many challenges arise with two wing configuration: lift production, design construction, and control systems. Control surfaces used in fixed wings can be used but at low Reynolds numbers they become less effective. In order to truly mimic insects with two wings, control mechanisms must be developed. Since MAVs are designed to navigate through confined spaces they need to have many degrees of freedom in motion. One way is to use a continuous variable transmission (CVT) mechanism, by integrating its infinite gear ratios to change the flapping …


Fluid-Structure Interaction Simulations Of A Flapping Wing Micro Air Vehicle, Alex W. Byrd Jan 2014

Fluid-Structure Interaction Simulations Of A Flapping Wing Micro Air Vehicle, Alex W. Byrd

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Interest in micro air vehicles (MAVs) for reconnaissance and surveillance has grown steadily in the last decade. Prototypes are being developed and built with a variety of capabilities, such as the ability to hover and glide. However, the design of these vehicles is hindered by the lack of understanding of the underlying physics; therefore, the design process for MAVs has relied mostly on trial-and-error based production. Fluid-Structure Interaction (FSI) techniques can be used to improve upon the results found in traditional computational fluid dynamics (CFD) simulations. In this thesis, a verification of FSI is first completed, followed by FSI MAV …


A Validation Study Of Sc/Tetra Cfd Code, Hongtao Yu Jan 2014

A Validation Study Of Sc/Tetra Cfd Code, Hongtao Yu

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The goal of this study is to validate the accuracy of the SC/Tetra CFD code by modeling four cases: a 2D zero pressure gradient flat plate, an axisymmetric separated boundary layer, flow over an NACA 0012 airfoil, and flow over an NACA 4412 airfoil trailing edge separation. The results will be compared to experimental data and CFL3D results. This study also investigates the sensitivity of SC/Tetra results to different set up details such as mesh resolution, turbulence model, and under-relaxation settings. Automation using the Visual Basic programming language was used to vary these set up details and efficiently process a …


Analysis Of A Fuel Cell Combustor In A Solid Oxide Fuel Cell Hybrid Gas Turbine Power System For Aerospace Application, Ryan R. Sinnamon Jan 2014

Analysis Of A Fuel Cell Combustor In A Solid Oxide Fuel Cell Hybrid Gas Turbine Power System For Aerospace Application, Ryan R. Sinnamon

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Over the last few years, fuel cell technology has significantly advanced and has become a mode of clean power generation for many engineering applications. Currently the dominant application for fuel cell technology is with stationary power generation. Very little has been published for applications on mobile platforms, such as unmanned aerial vehicles. With unmanned aerial vehicles being used more frequently for national defense and reconnaissance, there is a need for a more efficiency, longer endurance power system that can support the increased electrical loads onboard. It has already been proven by others that fuel cell gas turbine hybrid systems can …


Relating Microstructure To Process Variables In Beam-Based Additive Manufacturing Of Inconel 718, John Ryan Thompson Jan 2014

Relating Microstructure To Process Variables In Beam-Based Additive Manufacturing Of Inconel 718, John Ryan Thompson

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The advancement of laser or electron beam-based additive manufacturing requires the ability to control solidification microstructure. Previous work combined analytical point source solutions and nonlinear thermal finite element analysis (FEA) to explore the effects of deposition process variables on Ti-6Al-4V solidification microstructure. The current work seeks to extend the approach to Inconel 718, with the addition of Cellular Automaton-Finite Element (CAFE) models. Numerical data from finite element results are extracted in order to calculate accurate melt pool geometry, thus leading to corresponding cooling rates and thermal gradients. The CAFE models are used to simulate grain grown and nucleation, providing a …


Study On The Vortex Wake Of An Airfoil Equipped With Flexible Trailing Edge Fringes, Zhengkai He Jan 2014

Study On The Vortex Wake Of An Airfoil Equipped With Flexible Trailing Edge Fringes, Zhengkai He

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With the inspiration of owl's silent flight, a traditional airfoil S833 equipped with flexible fringes on the trailing edge is investigated through numerical simulation and experiments in a wind tunnel. The newly constructed airfoil is modeled and numerically investigated. An incompressible, 2D and viscous flow solver in the Computational Fluid Dynamics (CFD) software FLUENT is utilized to conduct the numerical simulation on the vortex flow feature in the wake of the airfoil. A User Defined Function code was applied to generate the defined motion of flexible fringes. The effects of the flapping frequency of the fringe and the deformation pattern …