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Full-Text Articles in Mechanical Engineering

Modeling Of Air Entrainment And Oxide Inclusion Formation During Pouring Of Metal Castings, Seyyed Hojjat Majidi Dec 2018

Modeling Of Air Entrainment And Oxide Inclusion Formation During Pouring Of Metal Castings, Seyyed Hojjat Majidi

Theses and Dissertations

Oxide inclusions are among the most commonly reported defects in ferrous and non-ferrous castings. They affect the surface quality, machinability, and mechanical performance of a cast part. Air entrainment during mold filling is the main source of the oxygen that is consumed in inclusion formation. A quantitative understanding of the formation mechanisms or the prediction of final amounts and locations of oxide inclusions in metal castings is not available. Ductile iron experiments are conducted to study the formation of oxide inclusions during pouring. Oxide inclusions are measured by serial sectioning of the solidified castings. The effect of different gating systems ...


Multiphase Macroscale Models For Macrosegregation And Columnar To Equiaxed Transition During Alloy Solidification, Mahdi Torabi Rad Dec 2018

Multiphase Macroscale Models For Macrosegregation And Columnar To Equiaxed Transition During Alloy Solidification, Mahdi Torabi Rad

Theses and Dissertations

In the field of metal casting, solute composition inhomogeneities at the macroscale are called macrosegregation, and the transition from the elongated grains in the outer portions of a casting to the more rounded grains in the center is termed Columnar to Equiaxed Transition (CET). Simultaneous prediction of macrosegregation and CET is still an important challenge in the field. One of the open questions is the role of melt convection on the CET and the effect of the CET on macrosegregation. A three-phase macroscale model for macrosegregation and CET was developed. The model accounts for numerous phenomena such as columnar dendrite ...


An Investigation Of Measurement Method And Phase Change In A Latent Heat Energy Storage Device, Jared Becker Aug 2018

An Investigation Of Measurement Method And Phase Change In A Latent Heat Energy Storage Device, Jared Becker

Theses and Dissertations

Exploring uses of two-phase mixtures as a way to store peak solar energy for off-peak usage is a novel approach that has been gaining attention in recent years to address the issues tied to solid fuel dependence. This research explores a “solar salt” mixture (40%wt KNO3 and 60%wt NaNO3) in an aluminum enclosure under two test conditions: conduction enhancement and no conduction enhancement. The central aim is to develop an understanding of thermal distributions and melt developments as the system moves from room temperature to 300 oC. Thermal pattern development is explored by experimentally observing a 2-D temperature ...


Structural And Functional Assessments Of Copd Populations Via Image Registration And Unsupervised Machine Learning, Babak Haghighi Aug 2018

Structural And Functional Assessments Of Copd Populations Via Image Registration And Unsupervised Machine Learning, Babak Haghighi

Theses and Dissertations

There is notable heterogeneity in clinical presentation of patients with chronic obstructive pulmonary disease (COPD). Classification of COPD is usually based on the severity of airflow limitation (pre- and post- bronchodilator FEV1), which may not sensitively differentiate subpopulations with distinct phenotypes. A recent advance of quantitative medical imaging and data analysis techniques allows for deriving quantitative computed tomography (QCT) imaging-based metrics. These imaging-based metrics can be used to link structural and functional alterations at multiscale levels of human lung. We acquired QCT images of 800 former and current smokers from Subpopulations and Intermediate Outcomes in COPD Study (SPIROMICS). A GPU-based ...


Modeling Of Shrinkage Porosity Defect Formation During Alloy Solidification, Vahid Khalajzadeh May 2018

Modeling Of Shrinkage Porosity Defect Formation During Alloy Solidification, Vahid Khalajzadeh

Theses and Dissertations

Among all casting defects, shrinkage porosities could significantly reduce the strength of metal parts. As several critical components in aerospace and automotive industries are manufactured through casting processes, ensuring these parts are free of defects and are structurally sound is an important issue. This study investigates the formation of shrinkage-related defects in alloy solidification. To have a better understanding about the defect formation mechanisms, three sets of experimental studies were performed. In the first experiment, a real-time video radiography technique is used for the observation of pore nucleation and growth in a wedge-shaped A356 aluminum casting. An image-processing technique is ...


Improving The Performance Of Finned Latent Heat Thermal Storage Devices Using A Cartesian Grid Solver And Machine-Learning Optimization Techniques, Michael Augspurger May 2018

Improving The Performance Of Finned Latent Heat Thermal Storage Devices Using A Cartesian Grid Solver And Machine-Learning Optimization Techniques, Michael Augspurger

Theses and Dissertations

The high energy density and stable temperature fields of latent heat thermal storage devices (LHTSD) make them promising in a range of applications, including solar energy storage, solar cooking, home heating and cooling, and thermal buffering. The chief engineering challenge in building an effective LHTSD is to find a way to complement the storage capabilities provided by the low-conductivity phase-change material with a suitable enhanced heat transfer mechanism.

The principal aim of this project is to develop a tool to improve the design of a small-scale LHTSD, such as one that might be used in solar cooking for a family ...


Local Properties And Rupture Characteristics Of Thoracic Aortic Aneurysm Tissue, Yuanming Luo May 2018

Local Properties And Rupture Characteristics Of Thoracic Aortic Aneurysm Tissue, Yuanming Luo

Theses and Dissertations

Ascending thoracic aortic aneurysms (ATAAs) are focal dilatations in the aorta that are prone to rupture or dissect. Currently, the clinically used indicator of the rupture risk is the diameter. However, it has been demonstrated that the diameter alone may not properly predict the risk. To evaluate the rupture risk, one must look into the local mechanical conditions at the rupture site and understand how rupture is triggered in the tissue which is a layered fibrous media. A challenge facing experimental studies of ATAA rupture is that the ATAA tissue is highly heterogeneous; experimental protocols that operate under the premise ...


High-Fidelity Multidisciplinary Design Optimization Of A 3d Composite Material Hydrofoil, Silvia Volpi May 2018

High-Fidelity Multidisciplinary Design Optimization Of A 3d Composite Material Hydrofoil, Silvia Volpi

Theses and Dissertations

Multidisciplinary design optimization (MDO) refers to the process of designing systems characterized by the interaction of multiple interconnected disciplines. High-fidelity MDO usually requires large computational resources due to the computational cost of achieving multidisciplinary consistent solutions by coupling high-fidelity physics-based solvers. Gradient-based minimization algorithms are generally applied to find local minima, due to their efficiency in solving problems with a large number of design variables. This represents a limitation to performing global MDO and integrating black-box type analysis tools, usually not providing gradient information. The latter issues generally inhibit a wide use of MDO in complex industrial applications.

An architecture ...


Microstructure Prediction Of Severe Plastic Deformation Manufacturing Processes For Metals, Ninggang Shen May 2018

Microstructure Prediction Of Severe Plastic Deformation Manufacturing Processes For Metals, Ninggang Shen

Theses and Dissertations

The objective of the research presented in this thesis has been to develop a physics-based dislocation density-based numerical framework to simulate microstructure evolution in severe plastic deformation (SPD) manufacturing processes for different materials. Different mechanisms of microstructure evolution in SPD manufacturing processes were investigated and summarized for different materials under dynamic or high strain rates over a wide temperature range. Thorough literature reviews were performed to clarify discrepancies of the mechanism responsible for the formation of nanocrystalline structure in the machined surface layer under both low-temperature and high-temperature conditions.

Under this framework, metallo-thermo-mechanically (MTM) coupled finite element (FE) models were ...


Multi-Parented End-Effectors In Optimization-Based Prediction Of Posture And Anthropometry, Anna Seydel Jan 2018

Multi-Parented End-Effectors In Optimization-Based Prediction Of Posture And Anthropometry, Anna Seydel

Honors Theses at the University of Iowa

Improving motion capture processing onto a virtual model is an important research area. Although there has been significant research in this field, little work has been done to determine posture and anthropometry simultaneously with the intent of visualizing the data on virtual models. Many existing techniques are less accurate when applying processed data to a virtual model for biomechanical analysis. This paper presents a novel approach that estimates posture and anthropometry using optimization-based posture prediction to determine joint angles and link-lengths of a virtual model. By including anthropometric design variables, this approach introduces flexible handling of innate variance in subject-model ...


Comparative Study Of Near-Infrared Pulsed Laser Machining Of Carbon Fiber Reinforced Plastics, Timothy Donald Heiderscheit Dec 2017

Comparative Study Of Near-Infrared Pulsed Laser Machining Of Carbon Fiber Reinforced Plastics, Timothy Donald Heiderscheit

Theses and Dissertations

Carbon fiber-reinforced plastics (CFRPs) have gained widespread popularity as a lightweight, high-strength alternative to traditional materials. The unique anisotropic properties of CFRP make processing difficult, especially using conventional methods. This study investigates laser cutting by ablation as an alternative by comparing two near-infrared laser systems to a typical mechanical machining process. This research has potential applications in the automotive and aerospace industries, where CFRPs are particularly desirable for weight savings and fuel efficiency.

First, a CNC mill was used to study the effects of process parameters and tool design on machining quality. Despite high productivity and flexible tooling, mechanical drilling ...


Experimental And Numerical Study On Failure Strength Of Aspirated Cell Membrane, Yang Wu Dec 2017

Experimental And Numerical Study On Failure Strength Of Aspirated Cell Membrane, Yang Wu

Theses and Dissertations

The objective of this work is to develop an innovative and quantitative method to study cell failure under fluidic pressure to understand cell membrane mechanical properties. Due to lack of experimental data related to cell failure property, the current research focuses on investigating the cell failure using a micro pipette aspiration experiment method to elaborate gradually increasing hydrostatic pressure to the cell causing the membrane to deform and eventually rupture. Based on our observation, the prostate cancer cells (PC-3) deformed into a deflated and flattened shape under higher hydrostatic pressure (249 Pa) while prostate epithelial cells (PrEC LH) cells generate ...


A Parallelized Diffuse Interface Solver With Applications To Meso Scale Simulation Of Suspensions, Fazlolah Mohaghegh Dec 2017

A Parallelized Diffuse Interface Solver With Applications To Meso Scale Simulation Of Suspensions, Fazlolah Mohaghegh

Theses and Dissertations

The ultimate goal of this research is to develop the capability of direct numerical simulation of a flow containing numerous rigid finite size particles. In order to reach this goal, we have implemented the smoothed profile method (SPM) in the University of Iowa in-house solver, pELAFINT3D and overcame several challenges related to the method. This includes a proposed formulation for the interface thickness and many validations and comparisons with experimental data as well as with a second-order accurate sharp interface method. As one of the issues related to low-density particles is the instability, SPM has been improved by developing to ...


Confidence-Based Model Validation For Reliability Assessment And Its Integration With Reliability-Based Design Optimization, Min-Yeong Moon Aug 2017

Confidence-Based Model Validation For Reliability Assessment And Its Integration With Reliability-Based Design Optimization, Min-Yeong Moon

Theses and Dissertations

Conventional reliability analysis methods assume that a simulation model is able to represent the real physics accurately. However, this assumption may not always hold as the simulation model could be biased due to simplifications and idealizations. Simulation models are approximate mathematical representations of real-world systems and thus cannot exactly imitate the real-world systems. The accuracy of a simulation model is especially critical when it is used for the reliability calculation. Therefore, a simulation model should be validated using prototype testing results for reliability analysis. However, in practical engineering situation, experimental output data for the purpose of model validation is limited ...


An Experimental Study Of The Global And Local Flame Features Created By Thermoacoustic Instability, Jianan Zhang Aug 2017

An Experimental Study Of The Global And Local Flame Features Created By Thermoacoustic Instability, Jianan Zhang

Theses and Dissertations

The current research focuses on the thermoacoustic instability of lean premixed combustion, which is a promising technique to inhibit Nitrogen Oxides (NOx) emission. Thermoacoustic instability describes the condition that the pressure oscillation is unusually high in the combustion device. It results from the coupling between pressure fluctuation and heat release oscillation, which experiences significant temporal and spatial variations. These variations are closely related to the flame shape deformation and critical in determining the trend of the global instability. Therefore, the current study aims to examine both the global and local flame features created by thermoacoustic instability.

The first part of ...


Ship Maneuvers With Discretized Propeller And Coupled Propeller Model/Cfd, Alireza Mofidi Aug 2017

Ship Maneuvers With Discretized Propeller And Coupled Propeller Model/Cfd, Alireza Mofidi

Theses and Dissertations

A high fidelity computational fluid dynamics approach to perform direct simulations of ship maneuvers is presented in this thesis. The approach uses dynamic overset grids with a hierarchy of bodies to enable arbitrary motions between objects, and overcome the difficulties in simulation of the moving rudder and rotating propeller. To better resolve propeller/rudder interaction a Delayed Detached Eddy Simulation turbulence model based on Menter’s SST is used. The methodology was implemented in the general purpose RANS/DES/DDES research code REX, and is applied to the KRISO Container Ship (KCS) with moving rudder and rotating propeller in deep ...


Flow Regimes And Instabilities Of Propeller Crashback, Matthew Pontarelli Aug 2017

Flow Regimes And Instabilities Of Propeller Crashback, Matthew Pontarelli

Theses and Dissertations

Crashback operation of a propeller is a common emergency slowing maneuver for ships and submarines. The reversing of the propeller while the vessel is moving forward results in large loads on the propeller blades and highly detached flow, which presents both practical concerns and fundamental fluid physics inquiries. This thesis contains a comprehensive numerical analysis of two propellers in crashback operation. Available numerical and experimental data for David Taylor Model Basin (DTMB) 4381 propeller are used for validation of the computational fluid dynamics solver used, REX. A second propeller, Maritime Research Institute Netherlands (MARIN) 7371R is used to classify the ...


Numerical Investigation Of A Plunging Airfoil, Matthew James Janechek Jul 2017

Numerical Investigation Of A Plunging Airfoil, Matthew James Janechek

Theses and Dissertations

This thesis investigates vortex dynamics of a plunging airfoil by studying the vorticity transport mechanisms of two-dimensional direct numerical simulations. The simulations were used to study a simplified flat airfoil in a freestream that was subject to pure plunging motion. Quantitative and qualitative analyses were used the validate the two-dimensional simulations and gain insight into the effects of eliminating three-dimensional physics in a nominally two-dimensional flow. Additionally, a parametric study was conducted to analyze the effects of Reynolds and Strouhal numbers on the transport of vorticity.


Supporting Energy Transitions And Miscanthus Program Development At The University Of Iowa, Kayley Christina Lain May 2017

Supporting Energy Transitions And Miscanthus Program Development At The University Of Iowa, Kayley Christina Lain

Theses and Dissertations

Miscanthus is a highly productive, low-input biofuel crop that supports agricultural diversification with improved performance for climate commitment, energy security, and water quality over first generation biofuels. Despite its high performance, no local or regional markets for the feedstock have formed in North America, and current climate-based productivity assessment methods lack the information farmers and decision-makers need to establish commercial scale bioenergy markets, programs, and thermal co-firing plans. This study develops a Miscanthus Suitability Rating and a transferable field-scale siting method, applied at 10 m resolution across the State of Iowa to assess miscanthus production potential and identify individual farms ...


Cfd Evaluation Of Cluster Specific Image Based Asthma Lung Features On Particle Transport And Hygroscopic Particle Growth Model Validation, Lawrence Joseph Leblanc May 2017

Cfd Evaluation Of Cluster Specific Image Based Asthma Lung Features On Particle Transport And Hygroscopic Particle Growth Model Validation, Lawrence Joseph Leblanc

Theses and Dissertations

Aerosolized drug delivery to the human lungs for asthma treatment has long been studied and yet the relationship between the delivery efficacy and the inter-subject variability due to gender, age, and disease severity remains unclear. A recent imaging-based cluster analysis on a population of asthmatic patients identifies four clusters with distinct structural and functional characteristics. The use of cluster membership to explore inter-subject variability by investigating numerically the air flow and particle transport in representative subjects of the asthmatic clusters on inhalation drug delivery in asthma sub-populations is proposed. Large-eddy simulations using computed tomography (CT)-based airway models were performed ...


Development Of Compact Collimation Device For Novel Scanning Beam Low-Energy Intraoperative Radiation Therapy (Sbiort) System For Pancreatic Cancer, Brennen Neal Wears May 2017

Development Of Compact Collimation Device For Novel Scanning Beam Low-Energy Intraoperative Radiation Therapy (Sbiort) System For Pancreatic Cancer, Brennen Neal Wears

Theses and Dissertations

Intraoperative radiation therapy (IORT) involves delivering high doses of radiation directly to tumors while sparing healthy tissues in a surgical setting. Current IORT systems lack the capability to deliver conformal radiation therapy. To overcome the limitations of non-conformal radiation therapy a collimation system is needed to conform the radiation beam to the shape of the tumor. This work presents the development of a compact collimator design intended for a scanning beam IORT (SBIORT) system. The SBIORT collimator design enables the delivery of variable square doses to the targeted region within the surgical cavity. The SBIORT collimator has a compact circular ...


A Ship Advancing In A Stratified Fluid: The Dead Water Effect Revisited, Mehdi Esmaeilpour May 2017

A Ship Advancing In A Stratified Fluid: The Dead Water Effect Revisited, Mehdi Esmaeilpour

Theses and Dissertations

A computational fluid dynamics (CFD) methodology is presented to predict density stratified flows in the near-field of ships and submarines. The density is solved using a higher-order transport equation coupled with mass and momentum conservation. Turbulence is implemented with a k-ε/k-ω based Delayed Detached Eddy Simulation (DDES) approach, enabling explicit solution of larger energy-containing vortices in the wake. Validation tests are performed for a two-dimensional square cavity and the three-dimensional stratified flow past a sphere, showing good agreement with available data. The near-field flow of the self-propelled Research Vessel Athena advancing in a stably stratified fluid is studied, as ...


Electrical Resistance Based Damage Modeling Of Multifunctional Carbon Fiber Reinforced Polymer Matrix Composites, Robert James Hart May 2017

Electrical Resistance Based Damage Modeling Of Multifunctional Carbon Fiber Reinforced Polymer Matrix Composites, Robert James Hart

Theses and Dissertations

In the current thesis, the 4-probe electrical resistance of carbon fiber-reinforced polymer (CFRP) composites is utilized as a metric for sensing low-velocity impact damage. A robust method has been developed for recovering the directionally dependent electrical resistivities using an experimental line-type 4-probe resistance method. Next, the concept of effective conducting thickness was uniquely applied in the development of a brand new point-type 4-probe method for applications with electrically anisotropic materials. An extensive experimental study was completed to characterize the 4-probe electrical resistance of CFRP specimens using both the traditional line-type and new point-type methods. Leveraging the concept of effective conducting ...


The Design Of An Electro-Mechanical Bicycle For An Immersive Virtual Environment, Oliver Stroh Jan 2017

The Design Of An Electro-Mechanical Bicycle For An Immersive Virtual Environment, Oliver Stroh

Honors Theses at the University of Iowa

Roughly 50,000 people are injured in bicycle collisions with motor vehicles each year, approximately 6,000 of these injuries involve children less than 14 years old. To better understand which factors put bicycling children at risk for motor vehicle collisions, researchers at the University of Iowa built a virtual environment that simulates the experience of riding through a town and crossing roads with motor vehicles traffic. The stationary bicycle, the focus of this report, replicates the pedal forces experienced by a rider. The stationary bike also provides the simulator with the bicycle’s velocity and steering angle. This report ...


Ship Airwake Computational Modeling Method Verification, Gregory Dooley Jan 2017

Ship Airwake Computational Modeling Method Verification, Gregory Dooley

Honors Theses at the University of Iowa

Computational Fluid Dynamics (CFD) simulations offer a feasible solution to resolving the behavior of ship airwake behavior in the interest of flight operations near a moving ship as opposed to large full scale experimental methods. Wind tunnel data has been collected for several wind-over-deck (WOD) conditions using the simple frigate shape (SFS2) conducted by the National Research Council of Canada. In order to test the ability of the CFD code REX to accurately simulate these conditions and provide meaningful data a comprehensive validation study was conducted. Wind tunnel data is provided for both a headwind and Green 45° scenario. Both ...


Flexible Multibody Dynamics Approach For Tire Dynamics Simulation, Hiroki Yamashita Dec 2016

Flexible Multibody Dynamics Approach For Tire Dynamics Simulation, Hiroki Yamashita

Theses and Dissertations

The objective of this study is to develop a high-fidelity physics-based flexible tire model that can be fully integrated into multibody dynamics computer algorithms for use in on-road and off-road vehicle dynamics simulation without ad-hoc co-simulation techniques. Despite the fact detailed finite element tire models using explicit finite element software have been widely utilized for structural design of tires by tire manufactures, it is recognized in the tire industry that existing state-of-the-art explicit finite element tire models are not capable of predicting the transient tire force characteristics accurately under severe vehicle maneuvering conditions due to the numerical instability that is ...


Thermomechanical Response Of Metal-Ceramic Graded Composites For High-Temperature Aerospace Applications, Phillip Eugene Deierling Dec 2016

Thermomechanical Response Of Metal-Ceramic Graded Composites For High-Temperature Aerospace Applications, Phillip Eugene Deierling

Theses and Dissertations

Airframes operating in the hypersonic regime are subjected to complex structural and thermal loads. Structural loads are a result of aggressive high G maneuvers, rapid vehicle acceleration and deceleration, and dynamic pressure, while thermal loads are a result of aerodynamic heating. For such airframes, structural members are typically constructed from steel, titanium and nickel alloys. However, with most materials, rapid elevations in temperature lead to undesirable changes in material properties. In particular, reductions in strength and stiffness are observed, along with an increase in thermal conductivity, specific heat and thermal expansion. Thus, hypersonic airframes are typically designed with external insulation ...


An Integrated Multibody Dynamics Computational Framework For Design Optimization Of Wind Turbine Drivetrains Considering Wind Load Uncertainty, Huaxia Li Dec 2016

An Integrated Multibody Dynamics Computational Framework For Design Optimization Of Wind Turbine Drivetrains Considering Wind Load Uncertainty, Huaxia Li

Theses and Dissertations

The objective of this study is to develop an integrated multibody dynamics computational framework for the deterministic and reliability-based design optimization of wind turbine drivetrains to obtain an optimal wind turbine gear design that ensures a target reliability under wind load and gear manufacturing uncertainties. Gears in wind turbine drivetrains are subjected to severe cyclic loading due to variable wind loads that are stochastic in nature. Thus, the failure rate of drivetrain systems is reported to be relatively higher than the other wind turbine components. It is known in wind energy industry that improving reliability of drivetrain designs is one ...


Experimental Study On The Impact Of Carbon Nanomaterials On Coke Formation, Matthew James Panzer Dec 2016

Experimental Study On The Impact Of Carbon Nanomaterials On Coke Formation, Matthew James Panzer

Theses and Dissertations

Thermal management is a major concern of jet engine development. During flight, engine components reach extreme temperatures as a result of frictional heating due to elevated airflow velocities. Jet fuel is used as a coolant to dissipate heat throughout the engine. This cooling process induces temperature and pressure increases within the fuel. At temperatures above 325°F, hydrocarbon fuels start to become thermally unstable, leading to the formation of solid deposits, known as coke. This paper outlines an experimental study that was conducted to further examine the coking mechanism. Specifically, a complete experimental setup and procedure was designed to simulate ...


Development Of High-Performance Cast Steel Crankshafts, Lucas Andrew Archer Dec 2016

Development Of High-Performance Cast Steel Crankshafts, Lucas Andrew Archer

Theses and Dissertations

To produce cast steel crankshafts, risering and gating systems are developed. Filling and solidification simulations of the steel crankshaft rigging are carried out to confirm that the rigging developed will produce a low porosity casting. A sand mold is created with Computer-aided design software, based on the developed crankshaft and rigging. Two prototype crankshafts are cast from the sand molds, and analyzed for porosity. The porosity analysis results are compared directly to the simulated porosity, and found to be in good agreement. From the analysis of the prototype crankshaft, rigging systems for a two-on and single-throw crankshaft are developed.

A ...