Engineering Commons^™

Generic Strategies To Implement Material Grading In Finite Element Methods For Isotropic And Anisotropic Materials, Ke Yu

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

We look at generic strategies to transfer material grading into finite element methods. Three strategies are proposed to transfer material grading into the finite element analysis. These strategies are node-centered, element-centered, and the definition of material grading through external functions. The process to achieve each strategy is stated, and examples are used to illustrate each strategy, and to compare them. The strategies are implemented in finite-deformation nonlinear elastic analysis.

Several examples are used to illustrate the implementation of each strategy for graded isotropic materials. For these examples, the results obtained from finite element models are compared with those obtained from …

Effect Of Extracellular Matrix (Ecm) Protein Micropatterns On The Behavior Of Human Neuroblastoma Cells, Ishwari Poudel

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Recent advances in patterning techniques and emerging surface microtechnologies have allowed cell micropatterning to control spatial location of the cells on a surface as well as cell shape, attachment area, and number of contacting neighbor cells. These parameters play important roles in cell cellular behaviors. Cell micropatterning has thus become one of the most important strategies for biomedical applications, such as, tissue engineering, diagnostic immunoassays, lab-on-chip devices, bio-sensing, etc., and cell biology studies as well. For neuronal cells, there have been attempts to distribute neuronal cells on specific patterns to control cell-to-cell interaction. However, there have been very limited understanding …

Anisotropic Thermal Property Measurement Of Carbon-Fiber/Epoxy Composite Materials, Tian Tian

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

This work originated from a need for understanding heat transfer in carbon-fiber/epoxy natural-gas tanks undergoing rapid heating during refilling. The dissertation is focused on the determination of the anisotropic thermal properties of carbon-fiber/epoxy composite materials for in-plane and through-thickness directions. An effective anisotropic parameter estimation system consisting of the 3ω experimental technique and an anisotropic two-dimensional heat transfer model is developed.

In the present work, the 3ω method, an experimental technique that has been well established to evaluate the thermal properties of isotropic materials, especially thin film materials, is extended to treat the thermal properties of bulk anisotropic …

Design, Analysis, And Testing Of In Vivo Surgical Robots, Tyler David Wortman

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Advances in technology have shaped the history of surgical procedures. Recent developments have allowed surgical procedures to become less invasive than traditional open procedures. The transition to Minimally Invasive Surgery (MIS) has resulted in decreased recovery times, improved cosmetic results, and reduced costs. For these reasons, there is interest in further reducing the invasiveness of surgical procedures by accessing the abdominal cavity through a single incision, such as with Laparoendoscopic Single-Site (LESS) surgery. Added complexities, such as unintuitive controls and limited dexterity, prevent the widespread adoption of LESS for complex surgical procedures. Multi-functional in vivo surgical robots have been designed …

Strength Of Polycrystalline Ceramics Under Shock Compression, Jianbin Zhu

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Determinations of Some polycrystalline ceramics’ strength properties and inelastic deformation mechanisms in the shocked state are critically important to the design and optimization of armor structures involving these materials. In this work, multiscale modeling and simulations have been carried out to study strength of the effects of polycrystalline microstructure, crystal anisotropy, porosity, and their interactions with microscopic deformation/damage mechanisms on the responses of several polycrystalline ceramics under shock compression and to extract their shock strengths from the wave profiles measured in the related plate impact shock wave experiments.

With a mesoscopic computational model, the roles of intragranular microplasticity and deformation …

Feasibility Analysis And Concept Development Of A Crash Cushion Diaphragm Structure For High-Speed Race Tracks, Curt Lee Meyer

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

A new diaphragm and dual guide rail system was designed for use in a crash cushion for high-speed race tracks. These structural components were designed to provide sufficient lateral support to redirect impacting vehicles and compress the energy-absorbing elements of the crash cushion. The primary design criteria stated that the diaphragm/guide rail system should be capable of withstanding a 100-kip lateral impact load. The guide rail was to be configured in order to not require replacement after a design impact event. Initial design and modeling resulted in two candidates for guide rail sections which were evaluated during physical testing. The …

Seamless Bridge And Roadway System For The U.S. Practice, Nima Ala

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Expansion joints are one of the main causes for high maintenance costs in bridges. The search for ideal expansion joints has proven fruitless. That is why it has been said that “the best joint is no joint”. A seamless bridge system is envisioned that results in bridges with long service lives by eliminating the joints over the entire length of the bridge, approach slab and a segment of the roadway called transition. All bridge thermal movements are dissipated to zero in the transition. The system is similar to a system developed in Australia but modifications had to be made to …

History Of The Biological Systems Engineering Program In Nebraska, University Of Nebraska-Lincoln, William E. Splinter

Tractor Testing Development and Research Documents

The Farm Machinery/Agricultural Engineering/Biological Systems Engineering program current and former faculty members at the University of Nebraska, as demonstrated here, has made a statewide, national, and worldwide impact on the efficient production of food. The quality of this recognition is evidenced best by peer professionals through recognized ASABE awards received by Nebraska alumni or professors. Since its inception in 1909 and until 2010, there have been 10 national presidents, 19 gold medal recipients and 33 named national award recipients. Currently there are 31 ASABE Fellows and two members of the National Academy of Engineering. This national recognition comes as a …

Thickness-Shear And Thickness-Twist Vibrations Of An At-Cut Quartz Mesa Resonator, Huijing He, Jinxi Liu, Jiashi Yang

Department of Mechanical and Materials Engineering: Faculty Publications

We study thickness-shear and thickness-twist vibrations of an AT-cut quartz plate mesa resonator with stepped thickness. The equations of anisotropic elasticity are used with the omission of the small elastic constant c56. An analytical solution is obtained using Fourier series from which the resonant frequencies, mode shapes, and energy trapping are calculated and examined. The solution shows that a mesa resonator exhibits strong energy trapping of thickness-shear and thickness-twist modes, and that the trapping is sensitive to some of the structural parameters of the resonator.

In Vivo Three-Dimensional Blood Velocity Profile Shapes In The Human Common, Internal, And External Carotid Arteries, Alexey Kamenskiy, Yuris A. Dzenis, Jason N. Mactaggart, Anastasia Desyatova, Iraklis I. Pipinos

Department of Mechanical and Materials Engineering: Faculty Publications

Objective: True understanding of carotid bifurcation pathophysiology requires a detailed knowledge of the hemodynamic conditions within the arteries. Data on carotid artery hemodynamics are usually based on simplified, computer-based, or in vitro experimental models, most of which assume that the velocity profiles are axially symmetric away from the carotid bulb. Modeling accuracy and, more importantly, our understanding of the pathophysiology of carotid bifurcation disease could be considerably improved by more precise knowledge of the in vivo flow properties within the human carotid artery. The purpose of this work was to determine the three-dimensional pulsatile velocity profiles of human carotid arteries. …

Increased Efficiency Of Low Band Gap Polymer Solar Cells At Elevated Temperature And Its Origins, Bin Yang, James Cox, Yongbo Yuan, Fawen Guo, Jinsong Huang

Department of Mechanical and Materials Engineering: Faculty Publications

Photovoltaic characteristics of a low bandgap polymer, poly[(4,4′-bis(2-lethylhexyl)dithieno-[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl], based bulk hetero-junction organic photovoltaic were investigated from room temperature (RT) to 145 °C to evaluate its applications in harsh environments. The power conversion efficiency was found to increase from 4.1% at RT to 4.5% at 105 °C with increased short circuit current density (J_sc) and fill factor (FF) despite the decreased open circuit voltage (V_oc). Detailed investigation revealed that J_sc and FF improvements were caused by the increased and balanced carrier mobilities at higher temperatures. The V_oc of the low bandgap …

Numerical Modeling Of Steady Burning Characteristics Of Spherical Ethanol Particles In A Spray Environment, Vaibhav Kumar Sahu, Vasudevan Raghavan, Daniel N. Pope, George Gogos

Department of Mechanical and Materials Engineering: Faculty Publications

A numerical study of steady burning of spherical ethanol particles in a spray environment is presented. A spray environment is modeled as a high temperature oxidizer stream where the major products of combustion such as carbon dioxide and water vapor will be present along with reduced amounts of oxygen and nitrogen. The numerical model, which employs variable thermophysical properties, a global single-step reaction mechanism, and an optically thin radiation model, has been first validated against published experimental results for quasi-steady combustion of spherical ethanol particles. The validated model has been employed to predict the burning behavior of the ethanol particle …

Rehabilitation And Exercise Machine, Judith M. Burnfield, Yu Shu, Adam P. Taylor, Thad W. Buster, Carl Nelson

Department of Mechanical and Materials Engineering: Faculty Publications

An improved rehabilitation and exercise machine is provided which allows a person with physical limitations, disabilities or chronic conditions to use the machine in order to rehabilitate their muscles, improve joint flexibility, and enhance cardiovascular fitness.

Effects Of Mass Layer Dimension On A Finite Quartz Crystal Microbalance, Y. P. Kong, Jinxi Liu, Huijing He, Jiashi Yang

Department of Mechanical and Materials Engineering: Faculty Publications

In this paper, we investigate free thickness-shear and thickness-twist vibrations of a finite crystal resonator of AT-cut quartz carrying a thin mass layer at the central portion of its top surface operating as a quartz crystal microbalance. The equations of anisotropic elasticity are used with the omission of the small elastic constant c56. An analytical solution is obtained using Fourier series from which the resonant frequencies, mode shapes and vibration confinement by the mass layer are calculated and examined.

Articulated Mechanism Design And Kinematics For Natural Orifice Translumenal Endoscopic Surgery Robot, Wei Jian Chin

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Natural Orifice Translumenal Endoscopic Surgery (NOTES) is a fairly recent surgical approach that eliminates the need for external incisions on the patient. NOTES takes the minimally invasive surgery paradigm a step further by using a natural orifice as the pathway to transport surgical tools to the surgical site and completely eliminating the need for even the smallest incision on the skin. Although the concept of NOTES has been in existence for the past decade, technological deficiencies prevent it from being widely accepted in human surgeries. A novel multifunctional robot for NOTES has been developed to overcome these limitations and make …

Six Degree Of Freedom Miniature In Vivo Robot For Laparoendoscopic Single-Site Surgery, Ryan L. Mccormick

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

The shift in surgery from open procedures to minimally invasive surgery (MIS) techniques have provided benefits of decreased recovery time, improved cosmetic results, and reduced costs. As advances in MIS move to minimize the number of external incisions, such as with Laparoendoscopic Single-Site (LESS) surgery, additional complexities are introduced. These complexities, including unintuitive controls, reduced dexterity, and limited workspace, hinder these methods from more widespread implementation in more complicated surgical procedures.

Through the use of a miniature in vivo robotic surgical platform designed for LESS surgery, these complexities can be mitigated, allowing for wider adoption of MIS by placing the …

Robotic Manipulator With Multiple Instruments For Natural Orifice Translumenal Endoscopic Surgery, Chi Min Seow

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

This thesis presents a novel robotic manipulator with multiple instruments for use in Natural Orifice Translumenal Endoscopic Surgery (NOTES). NOTES is a newly emerging surgical technique that eliminates external incisions on patients’ skin. As a result, better cosmetics, shorter recovery time, and reduced risk of external infection can be achieved.

Research has been ongoing in academia and industry to make this surgical procedure more feasible in human surgeries. Although several robotic platforms have been developed, none of them has the required capability to provide surgeons with the most appropriate tool in a safe and timely matter during surgery. This robotic …

Simulation And Control System Of A Railroad Track Power Harvesting Device, Kyle J. Phillips

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

With the vastness of existing railroad infrastructure, there exist numerous road crossings which are lacking warning light systems and/or crossing gates due to their remoteness from existing electrical infrastructure. Along with lacking warning light systems, these areas also tend to lack distributed sensor networks used for railroad track health monitoring applications. With the power consumption required by these systems being minimal, extending electrical infrastructure into these areas would not be an economical use of resources. This motivated the development of an energy harvesting solution for remote railroad deployment.

This thesis describes a computer simulation created to validate experimental on-track results …

Energy Harvesting Systems Design For Railroad Safety, Abolfazl Pourghodrat

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Railroad grade crossings are locations of significant interest for prevention of collisions, injuries and fatalities. Another area of concern is derailments resulting from mechanically deficient track structures. Many of these incidents occur in remote areas due to the lack of electrical infrastructure to power automated warning systems and/or track health monitoring sensor networks.

Providing electrical infrastructure to railroad crossings in remote areas is often not economical, and other alternative sources of electricity such as solar and wind energy are not reliable or robust. This motivated development of devices for in situ energy harvesting.

Initially, an improved mechanical energy harvesting device …

Fracture Analyses Of Aging Aircraft Structures And Human Aorta, Ananth Ram Mahanth Kasavajhala

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Understanding the behavior of fracture due to preliminary flaws in materials is essential to escalate the life and reliability of a structure. The present work is focused on investigating the influence of various structural parameters on the pre-crack growth stress state, initiation and propagation of flaws in two distinct fields of engineering that is, aging aircraft structural repair (aerospace) and the human aortic dissection (life sciences). Three dimensional finite element methodologies, coupled with linear elastic fracture mechanics (LEFM) formulation was utilized in both the cases.

A model of pre-cracked Al 7075 T6 plate was used to analyze pre- and post- …

Vertical Track Modulus Trending, Shane Michael Farritor, Sheng Lu

Department of Mechanical and Materials Engineering: Faculty Publications

Systems and methods for determining a trend in Vertical track modulus are disclosed in accordance with embodiments of the present invention. Vertical deflection data is collected along a particular section of railroad track. A first set of Vertical track modulus is determined, based in part, on the collected vertical deflection data. At a second time, vertical deflection data is again collected along the particular section of railroad track to be used in determining a second set of vertical track modulus. At least the first and second sets of Vertical track modulus are analyzed to determine a math ematical algorithm that …

A Study On Facility Planning Using Discrete Event Simulation: Case Study Of A Grain Delivery Terminal., Sarah M. Asio

Department of Industrial and Management Systems Engineering: Dissertations, Theses, and Student Research

The application of traditional approaches to the design of efficient facilities can be tedious and time consuming when uncertainty and a number of constraints exist. Queuing models and mathematical programming techniques are not able to capture the complex interaction between resources, the environment and space constraints for dynamic stochastic processes. In the following study discrete event simulation is applied to the facility planning process for a grain delivery terminal. The discrete event simulation approach has been applied to studies such as capacity planning and facility layout for a gasoline station and evaluating the resource requirements for a manufacturing facility. To …

A Virtual Supply Airflow Rate Meter In Rooftop Air Conditioning Units, Daihong Yu

Durham School of Architectural Engineering and Construction: Dissertations, Thesis, and Student Research

Virtual sensing technology aims to estimate difficult to measure, expensive, or new quantities by using multifarious mathematical models along with non-invasive and low-cost measurements. Such embedded intelligence is a key to improving the performance of building systems in terms of functionality, safety, energy efficiency, environmental impacts, and costs. Considering the progress that has been achieved over many various fields (e.g., process controls, automobiles, avionics, autonomous robots, telemedicine) within the last two decades, numerous intelligent features have been incorporated and enabled that would otherwise not be possible or economical.

To identify the potential opportunities and research/development needs of virtual sensing technology …

Supramolecular Nanolayer Reconfiguration After Molecular Intercalation, Alexandre Dhôtel, Hui Li, Lucia Fernandez-Ballester, Laurent Delbreilh, Boulos Youssef, Xiao Cheng Zeng, Li Tan

Department of Engineering Mechanics: Faculty Publications

We examined the structural reconfiguration after intercalating foreign additives, that is, tetramethoxysilane (TMOS), within already formed supramolecular nanolayers of hexadecyltrimethoxysilane (HDTMS). Our experiments indicated that the newly formed interdigitated structure is a thermodynamically more stable configuration. Even after the HDTMS formed initial bilayer-by-bilayer structures, mixing of these aggregates with foreign additives at room temperature can change the original structure to a more compact configuration (i.e., interdigitated). Our MD simulations further revealed that the most favorable organization for this interdigitated stacking appears to be a formation of relatively small domains of HDTMS and TMOS molecules, supporting our proposal of a heterogeneous …

The Effect Of Axial Conduction On Heat Transfer In A Liquid Microchannel Flow, Kevin D. Cole, Barbaros Çetin

Department of Mechanical and Materials Engineering: Faculty Publications

Analysis is presented for conjugate heat transfer in a parallel-plate microchannel. Axial conduction in the fluid and in the adjacent wall are included. The fluid is a constant property liquid with a fully-developed velocity distribution. The microchannel is heated by a uniform heat flux applied to the outside of the channel wall. The analytic solution is given in the form of integrals by the method of Green’s functions. Quadrature is used to obtain numerical results for the local and average Nusselt number for various flow velocities, heating lengths, wall thicknesses, and wall conductivities. These results have application in the optimal …

Analysis Of A Monolithic Crystal Plate Acoustic Wave Filter, Huijing He

Department of Mechanical and Materials Engineering: Faculty Publications

We study thickness–shear and thickness–twist vibrations of a finite, monolithic, AT-cut quartz plate crystal filter with two pairs of electrodes. The equations of anisotropic elasticity are used with the omission of the small elastic constant c56 . An analytical solution is obtained using Fourier series from which the res-onant frequencies, mode shapes, and the vibration confinement due to the electrode inertia are calculated and examined.

Ultrasonic Methods For The Characterization Of Complex Materials And Material Systems: Polymers, Structured Polymers, Soft Tissue And Bone, Charles Landais

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Understanding the characteristics and structure of materials is of importance in proper modeling and effective design of many products. Complex materials such as polymers, structured material systems, or biological materials provide a particular challenge to many of the traditional methods for doing this. In this dissertation I study the use of ultrasonic wave techniques to characterize several complex materials. These include plastically deformed and aged polycarbonate (PC), a structured PC plate with water filled cavities, bovine bone, and an elastomer used as a skin simulant. In each case, this work was part of a larger project that studied different aspects …

Mechanical Properties Of Pecvd Boron Carbide, Dhairyashil Aher

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

To the best of our knowledge, the mechanical properties of PECVD boron carbide (BC) grown using ortho-carborane as a source molecule have never been investigated before. Therefore, this thesis is an attempt to apply the bulge test and the nanoindentation technique for the mechanical characterization of PECVD BC thin films. Mechanical properties such as the Young’s modulus, hardness and residual stress were investigated. The bulge test system using an interferometry technique to measure the deflection of membrane has been designed. Commercially available LPCVD SiN_x membrane windows were used as a substrate to deposit BC films for the bulge test. …

Transverse Permeability Of Fibrous Porous Media, Ali Tamayol, Majid Bahrami

Department of Mechanical and Materials Engineering: Faculty Publications

In this study, the transverse permeability of fibrous porous media is studied both experimentally and theoretically. A scale analysis technique is employed for determining the transverse permeability of various fibrous matrices including square, staggered, and hexagonal arrangements of unidirectionally aligned fibers, as well as simple two-directional mats and simple cubic structures. In the present approach, the permeability is related to the porosity, fiber diameter, and tortuosity of the medium. In addition, the pressure drop in several samples of tube banks of different arrangements and metal foams are measured in the creeping flow regime. The pressure-drop results are then used to …

Improved Rehabilitation And Exercise Machine / Machine De Reeducation Et D'Exercice Amelioree, Judith M. Burnfield, Adam Taylor, Thad W. Buster, Carla A. Nelson, Yu Shu

Department of Mechanical and Materials Engineering: Faculty Publications

An improved rehabilitation and exercise machine is provided which allows a person with physical limitations, disabilities or chronic conditions to use the machine in order to rehabilitate their muscles, improve joint flexibility, and enhance cardiovascular fitness. An embodiment of the device includes a framework, a first and second crank arm, a first and second handle bar, a first and second foot pedal, a motor and pulley assembly, a first and second coupler link, and a motor controller with speed knob,