Mechanical Engineering Commons^™

Pulsed Optoacoustics In Solids, Zibiao Wei

Electrical & Computer Engineering Theses & Dissertations

Optoacoustic techniques are widely used to probe and characterize target materials including solids, liquids and gases. Included in such applications are diagnoses of thin films and semiconductor materials. The need to obtain greater spatial resolution requires the generation of shorter optoacoustic pulses. For such pulses, non-thermal effects may be quite important. On the other hand, even when an optoacoustic pulse is generated by an initially non-thermal technique, the thermal aspects become important in its evolution and propagation. The research undertaken in this Ph.D. dissertation included the generation and detection of optoacoustic signals through the thermal elastic mechanism. Several applications in …

Curvilinear Interface Methodology For Finite-Element Applications, Ollie James Rose

Mechanical & Aerospace Engineering Theses & Dissertations

Recent trends in design and manufacturing suggest a tendency toward multiple centers of specialty which results in a need for improved integration methodology for dissimilar finite element or CFD meshes. Since a typical finite element or CFD analysis requires about 50% of an engineers effort to be devoted to modeling and input, there is a need to advance the state-of-the-art in modeling, methodology. These two trends indicate a need to for the capability to combine independently-modeled configurations in an automated and robust way without the need for global remodeling. One approach to addressing this need is the development of interfacing …

Fabrication Of Thermoplastic Composite Laminates Having Film Interleaves By Automated Fiber Placement, Anthony Bruce Hulcher

Mechanical & Aerospace Engineering Theses & Dissertations

Experiments were carried out at the NASA Langley Research Center automated fiber placement facility to determine an optimal process for the fabrication of composite materials having polymer film interleafs. A series of experiments was conducted to determine an optimal process for the composite prior to investigation of a process to fabricate laminates with polymer films. The results of the composite tests indicated that a well-consolidated, void-free laminate could be attained. Preliminary interleaf processing trials were then conducted to establish some broad guidelines for film processing. The primary finding of these initial studies was that a two-stage process was necessary in …

Improving Co-Generation Plant Performance Using Computer Modeling Software: A Parametric Study, Gerald R. Munyan

Mechanical & Aerospace Engineering Theses & Dissertations

The desire to optimize plant performance continues to direct the goals of design and plant engineers associated with larger thermal systems. With the increasing availability of software designed for modeling thermal systems, the task of improving plant performance continues to develop. The ability to model a facility using a commercially available software package allows the design engineer and plant engineer to investigate the effects of variations in plant conditions or components on overall plant operations.

An analysis of the Kirk Lumber Company's co-generating facility was performed using the modeling program PROSIM written by the consulting engineering firm Endat Oy, of …

Compressible Flow Modeling In A Low Pressure Natural Gas Fuel Injector, Eugene D. White Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

In 1997, Siemens Automotive in Newport News, Virginia, conducted mass flow experiments on their DEKA IV natural gas fuel injector using nitrogen gas as the test fluid. The mass flow rates measured from the steady state flow experiments increased linearly with increasing upstream reservoir pressure. This relationship in the experimental data suggested that a choked flow condition must exist somewhere inside the injector.

To test this hypothesis, nitrogen gas flow through the internal passages of a fuel injector at steady state was simulated using computational fluid dynamics software. Several numerical models were constructed. Axisymmetric two-dimensional models were constructed of the …

Diffusion Problems In Wound Healing And A Scattering Approach To Immune System Interactions, Julia Suzanne Arnold

Mathematics & Statistics Theses & Dissertations

A theoretical model for the existence of a Critical Size Defect (CSD) in certain animals is the focus of the majority of this dissertation. Adam [1] recently developed a one-dimensional model of this phenomenon, and chapters I–V address the exist the CSD in a two-dimensional model and a three-dimensional model. The two dimensional (or 1-d circular) model is the more appropriate for a study of CSD's. In that model we assume a circular wound of uniform depth and develop a time-independent form of the diffusion equation relevant to the study of the CSD phenomenon. It transpires that the range of …

Process Flow Optimization Studies Through Discrete Event Simulation, Milind Chokshi

Electrical & Computer Engineering Theses & Dissertations

Computer-aided simulation has begun to emerge as a powerful tool for numerical analysis of the behavior and anticipated performance of industrial systems and their optimization. Applications include materials handling, storage and controls systems, prediction of manufacturing efficiencies, and production optimization. Simulations are used to test baseline models and subsequently analyze new production concepts, operating strategies, and planned procedures prior to costly implementation.

The study of process flows in a manufacturing environment is difficult due to its inherent stochastic nature. Breakdown of the sub-systems and failures of machines is a random process and needs to be solved based on concepts of …

An Integrated Engineering-Computation Framework For Collaborative Engineering: An Application In Project Management, Hisham Mohamed El-Sayed Abdelsalam

Mechanical & Aerospace Engineering Theses & Dissertations

Today's engineering applications suffer from a severe integration problem. Engineering, the entire process, consists of a myriad of individual, often complex, tasks. Most computer tools support particular tasks in engineering, but the output of one tool is different from the others'. Thus, the users must re-enter the relevant information in the format required by another tool. Moreover, usually in the development process of a new product/process, several teams of engineers with different backgrounds/responsibilities are involved, for example mechanical engineers, cost estimators, manufacturing engineers, quality engineers, and project manager. Engineers need a tool(s) to share technical and managerial information and to …

A Comparison Of Quasi-Static Indentation Testing To Low Velocity Impact Testing, Michael J. Douglas

Mechanical & Aerospace Engineering Theses & Dissertations

A static test method for modeling low-velocity foreign object impact events to composites would prove to be very beneficial to researchers since much more data can be obtained from a static test than from an impact test. In order to examine if this is feasible, a series of static indentation and low velocity impact tests were carried out and compared. Square specimens of many sizes and thicknesses were utilized to cover the array of types of low velocity impact events. Laminates with a rt/4 stacking sequence were employed since this is by far the most common type of engineering laminate. …

Effects Of Ventilation On Human Thermal Comfort In Rooms, Ahmed F. Alfahaid

Mechanical & Aerospace Engineering Theses & Dissertations

Nowadays, the majority of people spend up to 90% of their time indoors; as a result, the maintenance of optimal indoor climate conditions has become important for their overall health and comfort. The main goal of this study is to predict numerically the flow and temperature patterns and the human thermal comfort conditions in an indoor environment using displacement ventilation.

A Computational Fluid Dynamics (CFD) code has been used to analyze thermal comfort conditions for a fullscale ventilated room. Unstructured grids have been used to discretize the numerical domain. Before undertaking a detailed investigation, the code was validated by comparing …

Piezoceramic Actuator Placement For Acoustic Control Of Panels, Jeffrey S. Bevan

Mechanical & Aerospace Engineering Theses & Dissertations

Optimum placement of multiple traditional piezoceramic actuators is determined for active structural acoustic control of flat panels. The structural acoustic response is determined using acoustic radiation filters and structural surface vibration characteristics. Linear Quadratic Regulator (LQR) control is utilized to determine the optimum state feedback gain for active structural acoustic control. The optimum actuator location is determined by minimizing the structural acoustic radiated noise using a modified genetic algorithm. Experimental tests are conducted and compared to analytical results.

Anisotropic piezoceramic actuators exhibit enhanced performance when compared to traditional isotropic piezoceramic actuators. As a result of the inherent isotropy, these advanced …

Suppression Of Post-Buckling Deflection And Panel-Flutter Using Shape Memory Alloy, Mohammad Tawfik Abo El So-Oud

Mechanical & Aerospace Engineering Theses & Dissertations

A novel concept proposed is the use of Shape Memory Alloy (SMA) to reduce the panel thermal deflection and flutter responses. SMA has unique ability to recover large prestrains completely when the alloy is heated (by aerodynamic heating in the present case) above the austenite start temperature A_s. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained.

In this thesis, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on von Karman strain displacement relation is utilized to study the effectiveness of SMA …

Stratal Architecture In A Prograding Shoreface Deposit, Eastern Shore, Va: Relationship To Grain Size, Permeability, And Facies Distribution, Andrew C. Miller

OES Theses and Dissertations

A fundamental concern of the stratigrapher is to develop predictive models of stratigraphic organization. In sedimentology one of the most significant problems that has yet to be resolved is the fact that there is a lack of quantitative information regarding the relationship between geometry of beds, thickness of beds, grain size and sedimentary structures in sandy environments, especially shallow marine deposits. Scientists have also realized the need to correlate quantitative permeability to sedimentary structures and scales of stratigraphic organization. The purpose of the study is to investigate the scales of stratigraphic organization that control the variation of grain size and …

An Experimental Investigation Into The Effect Of Clearance And Torque On Load Sharing In A Bolted Joint, Jerry B. Robertson

Mechanical & Aerospace Engineering Theses & Dissertations

The shear load experienced by each bolt in a multi-fastener bolted butt joint is a percentage of the total load applied to the joint. Joint failure can be premature when one fastener is subjected to a disproportional amount of the total load. Conversely, the ultimate load the joint can endure may be increased if the distribution of loads can be equalized by some means. In this investigation, two and four fastener butt joints were studied. An instrumented bolt was constructed that could measure the bending stresses in the bolt associated with the bearing load. That data was converted into force …

Continuous Adjoint Sensitivity Analysis For Aerodynamic And Acoustic Optimization, Kaveh Ghayour

Mechanical & Aerospace Engineering Theses & Dissertations

A gradient-based shape optimization methodology based on continuous adjoint sensitivities has been developed for two-dimensional steady Euler equations on unstructured meshes and the unsteady transonic small disturbance equation. The continuous adjoint sensitivities of the Helmholtz equation for acoustic applications have also been derived and discussed.

The highlights of the developments for the steady two-dimensional Euler equations are the generalization of the airfoil surface boundary condition of the adjoint system to allow a proper closure of the Lagrangian functional associated with a general cost functional and the results for an inverse problem with density as the prescribed target. Furthermore, it has …

Setpoint Tracking Predictive Control In Chemical Processes Based On System Identification, Sinchai Chinvorarat

Mechanical & Aerospace Engineering Theses & Dissertations

A Kraft recovery boiler in a pulp-paper mill provides a means for recovery of the heat energy in spent liquor and recovery of inorganic chemicals while controlling emissions. These processes are carried out in a combined chemical recovery unit and steam boiler that is fired with concentrated black liquor and which produces molten smelt. Since the recovery boiler is considered to be an essential part of the pulp-paper mill in terms of energy resources, the performance of the recovery boiler has to be controlled to achieve the highest efficiency under unexpected disturbances.

This dissertation presents a new approach for combining …

Computation Of Flame Base Height Of A Turbulent Diffusion Flame Resulting From A Methane Jet, A. S. Kheireddine, S. K. Chaturvedi, T. O. Mohieldin

Mechanical & Aerospace Engineering Faculty Publications

This work summarizes numerical results for a diffusion flame formed from a cylindrical tube fuel injector, issuing a gaseous methane jet vertically in a quiescent atmosphere. The primary objective is to predict the flame base height and other flame characteristics as a function of the fuel jet velocity. A finite volume scheme is used to discretize the time-averaged Navier-Stokes equations for the reacting flow resulting from the turbulent fuel jet motion. The turbulent stresses, and heat and mass fluxes are computed from a Reynolds stress turbulence model. A chemical kinetics model involving two-step chemistry is employed for the oxidation of …

Multidisciplinary Sensitivity Analysis And Design Optimization Of Flexible Wings Using The Euler Equations On Unstructured Grids, Arunkumar Satyanarayana

Mechanical & Aerospace Engineering Theses & Dissertations

Aeroelasticity is a classical discipline. However, even with recent advancement in computational technology, it still remains a challenging discipline. This is particularly true when aeroelasticity problems are solved in a loosely coupled manner. The advantage of a loosely coupled scheme is that the legacy codes of computational fluid dynamics (CFD) and computational structural mechanics (CSM) can be preserved and used as independent modules in solving the desired aeroelasticity problems. In such a scheme, maintaining proper data transfer (load transfer and deformation tracking between CFD and CSM codes) is crucial in ensuring successful coupled solutions. This can be a challenging task …

Computational Modeling Of Airborne Noise Demonstrated Via Benchmarks, Supersonic Jet, And Railway Barrier, Moumen Idres

Mechanical & Aerospace Engineering Theses & Dissertations

In the last several years, there has been a growing demand for mobility to cope with the increasing population. All kinds of transportation have responded to this demand by expanding their networks and introducing new ideas. Rail transportation introduced the idea of high-speed trains and air transportation introduced the idea of high-speed civil transport (HSCT). In this expanding world, the noise legislation is felt to inhibit these plans. Accurate computational methods for noise prediction are in great demand.

In the current research, two computational methods are developed to predict noise propagation in air. The first method is based on the …

Skin-Stiffener Separation In Buckled Composite Plates And Shallow Shells, Mark Edward Robeson

Mechanical & Aerospace Engineering Theses & Dissertations

The development of an approximate analysis for predicting stresses in the skin-stiffener interface region of composite plates and shallow shells is presented. The analysis determines interlaminar normal stress and transverse shear stresses in the direction of the stiffener axial coordinate and the direction of the inplane coordinate perpendicular to the stiffener axis. The analysis accounts for skin-stiffener interfaces with nonzero thickness and for curvature in the skin and stiffener. The interlaminar normal stress and transverse shear stresses at the interface are applied to the lower face of the skin and the upper face of the stiffener flange as unknown functions, …

Design Optimization Of Magnetic Bearings And Magnetic Suspension Systems, V. Dale Bloodgood Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Magnetic suspension systems were first demonstrated as practical by Holmes and Beams in the 1930's. Since then, numerous academic researchers have worked with various types of these systems. Commercial applications have largely been limited to magnetic bearings for rotating machinery. Other applications that have held considerable promise include wind tunnel model suspensions, space payload pointing and vibration isolation systems, satellite momentum storage and control devices and electromagnetic launch systems. However, none of these have progressed significantly beyond the prototype stage. Maglev trains have not reached serious commercial service but are being aggressively developed in Germany and Japan.

Design methods for …

The Solution Of Hypersingular Integral Equations With Applications In Acoustics And Fracture Mechanics, Richard S. St. John

Mathematics & Statistics Theses & Dissertations

The numerical solution of two classes of hypersingular integral equations is addressed. Both classes are integral equations of the first kind, and are hypersingular due to a kernel containing a Hadamard singularity. The convergence of a Galerkin method and a collocation method is discussed and computationally efficient algorithms are developed for each class of hypersingular integral equation.

Interest in these classes of hypersingular integral equations is due to their occurrence in many physical applications. In particular, investigations into the scattering of acoustic waves by moving objects and the study of dynamic Griffith crack problems has necessitated a computationally efficient technique …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

Reduction Of Thermal Deflection And Random Response Of Composite Structures With Embedded Shape Memory Alloy At Elevated Temperature, Zhiwei Zhong

Mechanical & Aerospace Engineering Theses & Dissertations

A feasibility study on the reduction of thermal deflection and random response of the composite structures using shape memory alloys (SMA) at elevated temperatures is presented in this dissertation. The characteristics of SMA are introduced and the structural problems, static and dynamic, of SMA fiber reinforced composites are investigated. The stress-strain relations are developed for a composite lamina with embedded SMA fibers. The finite element system equations including shape memory effect are derived. A consistent two-step solution procedure is developed for solving the static and dynamic problems of composite structures with embedded SMA fibers subjected to combined acoustic and thermal …

Material Evaluation By Pulsed Diode Laser Optoacoustics, Xiaodong Xu

Electrical & Computer Engineering Theses & Dissertations

Pulsed diode laser optoacoustic diagnostics were carried out to characterize solid sample materials. The apparatus developed is compact, portable, cost-effective and therefore very promising for both industrial as well as laboratory applications. To our knowledge, this is the first time that optoacoustic characterization and measurement have been performed with a diode laser. The method was successfully applied to measure the thickness of a multilayer structure non-intrusively. Internal cracks of the material were detected by this technique.

A theory for optoacoustic signal generation, propagation and detection is given. A numerical analysis technique is developed to solve for the expected signal. In …

Ir-Hot Gas Heat Source For Automated Tow Placement, Ray Walton Grenoble

Mechanical & Aerospace Engineering Theses & Dissertations

A series of five experiments on the NASA Langley automated tow placement robot revealed stagnation of gas flow in the nip region. Since the torches could not heat effectively in the nip region, the roller temperature was the dominant influence on interlaminar bond strength. The roller temperatures required for high bond strength caused resin and fiber on the panel top surface to adhere to the compaction roller. Resin and fiber was pulled from the panel surface and wrapped around the roller, which was a severe processing problem. A supplemental radiant heat source was designed to permit reductions in roller temperature. …

Analysis And Testing Of Plates With Piezoelectric Sensors And Actuators, Jeffrey S. Bevan

Mechanical & Aerospace Engineering Faculty Publications

Piezoelectric material inherently possesses coupling between electrostatics and structural dynamics. Utilizing linear piezoelectric theory results in an intrinsically coupled pair of piezoelectric constitutive equations. One equation describes the direct piezoelectric effect where strains produce an electric field and the other describes the converse effect where an applied electrical field produces strain. The purpose of this study is to compare finite element analysis and experiments of a thin plate with bonded piezoelectric material. Since an isotropic plate in combination with a thin piezoelectric layer constitutes a special case of a laminated composite, the classical laminated plate theory is used in the …

Building Lms Adaptive Filters With Register-Based Fpgas, Li Ding

Electrical & Computer Engineering Theses & Dissertations

In this thesis, an 8-bit least mean squares (LMS) adaptive digital filter with 16 coefficients is implemented on a single FPGA, using the MaxPlus+2 design environment. The system is constructed as a hierarchical structure, using four different levels of design hierarchy. Subdesigns at each level of the hierarchy project are complied, fitted and simulated to test and verify their functional correctness. The complete system is tested and verified by checking the MaxPlus+2 simulator results against fixed-point integer arithmetic simulations written in Matlab. The resulting adaptive filter is subsequently mapped to the Alters FLEX I OK20TC144-3 device, resulting in a 14,500 …

Thin-Layer Prestressed Composite Ferroelectric Driver And Sensor Characterization With Application To Separation Flow Control, Karla M. Mossi

Mechanical & Aerospace Engineering Theses & Dissertations

Experiments were conducted in two different stages--general piezoelectric actuator characterization and flow separation control applications. The characterization of the piezoelectric devices was performed in several stages, due to the many variables that affect performance. The first stage of the characterization consisted of tests conducted on 13 different THUNDER^TM (thin-layer composite unimorph ferroelectric driver and sensor) configurations. These configurations consisted of a combination of 1, 3, 5, 7, and 9 layers of 25μ thick aluminum as backing material, with and without a top layer of 25μ aluminum. All of these configurations used the same piezoelectric ceramic wafer (PZT-5A) with dimensions …

Inversion And Analysis Of Remotely Sensed Atmospheric Water Vapor Measurements At 940nm, Jack Cutler Larsen

Mechanical & Aerospace Engineering Theses & Dissertations

The understanding and acceptance of remotely sensed atmospheric data depends strongly on the steps taken to characterize experiment error and validate observations through comparisons to other independent measurements. A formal error analysis of the Stratospheric Aerosol and Gas Experiment II (SAGE II) water vapor operational inversion algorithm is performed and compared to previous results. Random measurement errors were characterized by segmented least-squares profile fitting of the slant path absorption which found the error to be uncorrelated in the stratosphere with estimated variances significantly smaller than expected from 18-30 km. Estimates of null space error were developed from radiosonde hygrometers in …