Engineering Commons^™

Rapid Relaxation Of An Axisymmetric Vortex, Andrew J. Bernoff, Joseph F. Lingevitch

All HMC Faculty Publications and Research

In this paper it is argued that a two‐dimensional axisymmetric large Reynolds number (Re) monopole when perturbed will return to an axisymmetric state on a time scale (Re^1/3) that is much faster than the viscous evolution time scale (Re). It is shown that an arbitrary perturbation can be broken into three pieces; first, an axisymmetric piece corresponding to a slight radial redistribution of vorticity; second, a translational piece which corresponds to a small displacement of the center of the original vortex; and finally, a nonaxisymmetric perturbation which decays on the Re^1/3 time scale due to a shear/diffusion …

Artificial Dielectric Materials : Synthesis And Optical Characterization Of Small Metal Clusters Embedded In Polymeric Matrix, Nazneen Karim Shilpee

Theses

This study is concerned with the fabrication of films made of gold, nickel, and silicon clusters dispersed in a polymeric matrix. The films were fabricated by use of metal or semiconductor sputtering and plasma polymerization of Methyl Methacrylate monomer in a capacitively coupled RF (13.56 MHz) sputtering system. Optical transmittance and optical reflectance were measured as a function of wavelength. The optical absorption of metal or silicon clusters was studied as a function of cluster size. Cluster size and content were determined from Transmission Electron Micrographs (TEM). The absorption band resulting from a plasma resonance in the clusters was found …

Design And Analysis Of Constrained Layer Damping Treatments For Bending And Torsion, Kimberly J. Balkema

Theses and Dissertations

In this dissertation, different aspects of constrained layer damping treatments on beams of various geometries are studied. First, the optimal length of a constrained layer damping treatment mounted on a surface in linear strain is identified as a function of the relative stiffnesses of the damping layers and the non-uniformity of the surface stain. The analysis extends previous work that considered the case of uniform surface strain. Sixth order sandwich beam theory is then modified for use with a rectangular beam covered with a segmented constrained layer damping treatment. Non-dimensional variables are used to simplify the form of the problem. …

Development Of Vibration And Sensitivity Analysis Capability Using The Theory Of Structural Variations, Ting-Yu Rong

Mechanical & Aerospace Engineering Theses & Dissertations

In the author's previous work entitled "General Theorems of Topological Variations of Elastic Structures and the Method of Topological Variation," 1985, some interesting properties of skeletal structures have been discovered. These properties have been described as five theorems and synthesized as a theory, called the theory of structural variations (TSV). Based upon this theory, an innovative analysis tool, called the structural variation method (SVM), has been derived for static analysis of skeletal structures (one-dimensional finite element systems).

The objective of this dissertation research is to extend TSV and SVM from one-dimensional finite element systems to multi-dimensional ones and from statics …

Investigation Of Computational And Spectral Analysis Methods For Aeroacoustic Wave Propagation, Florence Odile Vanel

Mechanical & Aerospace Engineering Theses & Dissertations

Most computational fluid dynamics (CFD) schemes are not adequately accurate for solving aeroacoustics problems, which have wave amplitudes several orders of magnitude smaller yet with frequencies larger than the flow field variations generating the sound. Hence, a computational aeroacoustics (CAA) algorithm should have minimal dispersion and dissipation features. A dispersion relation preserving (DRP) scheme is, therefore, applied to solve the linearized Euler equations in order to simulate the propagation of three types of waves, namely: acoustic, vorticity, and entropy waves. The scheme is derived using an optimization procedure to ensure that the numerical derivatives preserve the wave number and angular …

Stress Fields In Composites With A Variable Interphase Under Thermo-Mechanical Loadings, Nianfeng Chen

Mechanical & Aerospace Engineering Theses & Dissertations

An interphase in a composite material has a important role for the composite performance. It influences directly or indirectly the strength, fatigue performance and effective properties of the composite. Recently, interphase has drawn increasing attention in composite mechanics. To the best of our knowledge, however, no one seems to have considered the effect of the variable material prope1ty in the interphase on the stress field in the composite material. In this research, the stress fields are determined in the continuous fiber composite and the particulate composite by using the four concentric circular cylinders model and the four phase spheres model, …

An Experimental And Analytical Investigation Of The Iosipescu Shear Test For Composite Materials, Barry Stuart Spigel

Mechanical & Aerospace Engineering Theses & Dissertations

Mechanical properties of composite materials under shear loading are difficult to determine. The Iosipescu Shear test, originally proposed for metals, has in recent years been applied to composites. It has the advantages of small specimen size, simple loading and a reasonably uniform shear stress in the test section.

The purpose of this work is to study the validity of the Iosipescu test method for measuring the shear modulus and shear strength of composites. Finite element analyses indicate that optimum specimen geometry and load locations depend upon the degree of orthotropy of the composite. Test results for a quasi-isotropic graphite/epoxy laminate …

Quality Problems Facing Tanzanian Industrial Firms, M Msafiri

Tanzania Journal of Engineering and Technology (TJET)

This paper reports on the results of a study of quality problems facing Tanzanian industrial firms. The results show that Tanzanian firms do not set goals with respect to quality and quality management, thus their qual- ity performance is generally poor. A Ithough there are a number of opera- tional problems constraining the companies, the main problems lie with the internal management of the quality function. Extensive ideas and sug- gestions for improving the performance of the quality function are given.

Influence Of Turbulence On Methane-Air Flame Speed, E Mushi

Tanzania Journal of Engineering and Technology (TJET)

Experimental study Of the influence qfturbulence on flame speed for meth- ane-air mixtures has been conducted in afan stirred bomb using schlieren photography. It has been observed that turbulence increases flame speed but above KLe=O. 18 (KLe is the product Of the dimensionless Karlovitz flame stretch factor and the Lewis number) turbulence quenches the flame. Inminarflame kernel is observed to prevail in the early stages of flame development in a turbulent mixture. Further, the laminar burning velocity plays a significant role in turbulent combustion. It is proposed that the increase in flame speed is a result of flame wrinkling.

An Alternative Method Of Interfacing A Dc Motor To A Microprocessor For Mo- Tion Control, M Selekwa

Tanzania Journal of Engineering and Technology (TJET)

A Simple and cheap alternative method Of interfacing a permanent mag- net dc motor to a motion control using switch- ing transistor motor drivers is presented. This method involves the use Of very few transistor-transistor logic (TTL) devices and a 555 timer to pro- duce a pulse width modulated (P WM) signal which is required by the mo- ror driver. The motor driver in this case should be of an H-bridge type. Like other methods currently in use, it relieves the MPU of all timing func- tions which are necessary in the generation of P WM signals. The present method, …

Transverse Stress Effects For Laminated Composite Beams In Bending, Christine Chatterton Schleicher

Mechanical & Aerospace Engineering Theses & Dissertations

A higher-order theory and an associated finite element formulation are developed for analysis of laminated planar beams in bending. The higher-order theory incorporates both transverse normal stress and transverse shear stress, and is developed using two approaches. The first approach is based on assuming the transverse normal strain distribution to be a cubic function through the beam thickness, while the second approach is based on assuming the transverse normal stress distribution to be a cubic function through the beam thickness. In both approaches, the transverse shear strain distribution is assumed to be a quadratic function through the beam thickness. Theoretical …

A Direct Numerical Simulation Of Vortex Breakdown Induced Tail Buffet, Steven James Massey

Mechanical & Aerospace Engineering Theses & Dissertations

A simulation of tail buffet is presented for a delta wing-vertical tail configuration. Flow conditions are chosen such that the wing primary-vortex cores experience vortex breakdown and the resulting turbulent wake flow impinges on the vertical tail. The dimensions and material properties of the vertical tail are chosen such that the deflections are large enough to insure interaction with the flow, and the natural frequencies are high enough to facilitate a practical computational solution. This multidisciplinary problem is solved sequentially for the fiuid flow, the elastic deformations and the grid displacements. The fluid flow is simulated by time accurately solving …

Application Of Machine Learning Principles To Modeling Of Nonlinear Dynamic Systems, Murray R. Clark

Journal of the Arkansas Academy of Science

A method for the development of mathematical models for dynamic systems with arbitrary nonlinearities from measured data is described. The method involves the use of neural networks as embedded processors in dynamic system simulation models. The technique is demonstrated through generation of models for anharmonic oscillators described by the Duffing Equation and the Van der Pol Equation from measured input/output data. It is shown that high quality models of these systems can be developed using this technique which are efficient in terms of model size. Using neural networks as embedded processors, accurate models of the Duffing Oscillator and the Van …

Permeability Control Using Polymer Impregnation In Sandy Soil, Mohamed Salah Mohamed Ahmed

Archived Theses and Dissertations

No abstract provided.

Thermodynamics And Transport Proper- Ties Analysis Of Natural Gas From Songosongo In Kilwa- Tanzania, G Mrema

Tanzania Journal of Engineering and Technology (TJET)

Analysis ofthermodynamics and transport properties was carried outfor six natu- ral gas samples from Songosongofield in Kilwa - Tanzania using PRO/II simula- for. Properties of most interest in gas processing (due to their influence on the sales value) such as density, specific gravity, critical parameters, bubble point and dew point, enthalpy, latent heat of vaporisation, molecular weight, boiling point and phase were investigated. In addition composition of the gas was com- pared with that from elsewhere. The gas was assumed to be at a temperature of 30C and a pressme of 150 bar before pressure let down station. Results indicated …

Practical Aspects In Sensing Vrm Magneti- Sation Characteristics For Rotor Position Detection, N Mvungi

Tanzania Journal of Engineering and Technology (TJET)

The detection of rotor position (stator/roror poles overlap) in a variable reluc- tance motor using the dependence of permeance on rotor position is the core of the effort to eliminate the need of a physical position sensor in the rotor shaft in the positional feedback operation of the motor. The reliability of the whole proc- ess Of eliminating the need of a physical sensor rests squarely On the ability to measure the instantaneous permeance ofa phase when the motor is in operation and at stand still. This paper presents an experimental investigation on the in- triguing problems of obtaining repeatable …

Simultaneous Design Of Active Vibration Control And Passive Damping, Michele Lynn Devereaux Gaudreault

Theses and Dissertations

A modified form of the standard linear quadratic regulator LQR cost functional is used to optimally blend active vibration control and passive structural damping, whether viscous or viscoelastic. Viscoelastic damping is first modelled by a standard linear model, and then by a fractional derivative model. For the viscous damping case and the classically modelled viscoelastic damping case, a sub-optimal closed form solution is derived that is independent of the initial conditions. An iterative technique that minimizes the average value of the cost functional and one that minimizes the maximum value are developed. Both techniques are applicable to viscous and viscoelastic …

Investigation Of Tension-Compression Fatigue Behavior Of A Cross-Ply Metal Matrix Composite At Room And Elevated Temperatures, Elizabeth A. Boyum

Theses and Dissertations

This research, the first load-controlled tension-compression fatigue testing to be performed on a MMC, extends the existing knowledge of MMC fatigue damage mechanisms to include the tension compression loading condition. To accomplish this, a (0/90)2, SCS-6/Ti-15-3 laminate was subjected to tension- tension fatigue at room temperature, and tension-compression fatigue at both room temperature and 427°C. Stress and strain data was taken to evaluate the macro-mechanic behavior of the material. Microscopy and fractography were performed to characterize the damage on a micro-mechanic level. On a maximum applied stress basis, the room temperature tension-tension specimens had longer fatigue lives than the room …

Influence Of Embedded Optical Fibers On Compressive Strength Of Advanced Composites, Stefan B. Dosedel

Theses and Dissertations

This study investigated the effects of embedding optical fibers into advanced composite materials. This combination was meant to simulate 'smart structures' that have been shown to sense several different variables in the composite including strain, temperature, and damage. A laminate orientation taken from an existing aircraft structure was used to fabricate sixteen groups of specimens which were subjected to compression testing in an IITRI fixture to determine the ultimate compressive strength and modulus of elasticity. Ten of these groups were fabricated with optical fibers while the other six were control groups and contained no optical fibers. This study showed that …

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite Under Strain Controlled Tension-Tension And Tension-Compression Loading, James J. Gudaitis

Theses and Dissertations

This stuidy investigates the fatigue response of a cross-ply [0/90]_2s Nicalon/Calcium Aluminosillicate (Nicalcc/CAS) ceramic matrix composite at room temperature under strain controlled tension-tension and tension-compression fatigue loading. The primary objectives were to determine strain fatigue limits for both loading cases and to complete a fatigue life diagram (Δe-N) for all tests. Failure mechanisms were also studied. The average initial modulus value for this lay-up was 120 GPa. The ultimate tensile strain was 0.00988 mn/mm (285 MPa). Eight tests were conducted with maximum strains that ranged from 0.00300 mm/mm to 0.00722 mm/mm. The tension-tension fatigue limit was found to be …

Investigation Of Compressive Behavior For Metal Matrix Composites With A Circular Hole, Janet L. Gooder

Theses and Dissertations

This study investigated the notched and unnotched macromechanical response due to micromechanical behavior of [0/±45/90]_S SCS-6/β 21 S and [0/90] _2S Sigma/β 21S subjected to static compressive loads at room temperature. The stress-strain behavior and mechanical response in the presence of a circular hole was examined. A clear description of the progressive nature of damage, which ultimately resulted in failure, was provided. The effect of elevated temperature was shown for SCS-6/β 21S. The ultimate compressive strength and elastic modulus were reported for both MMCs. Sigma/β 21S and SCS-6/β 21S were mildly notch sensitive at room temperature. Notch sensitivity of …

Fatigue Behavior Of A Cross-Ply Ceramic Matrix Composite At Elevated Temperatures Under Tension-Tension Loading, Richard J. Tuznik

Theses and Dissertations

A study was conducted which investigated the behavior of a Nicalon/ Calcium-Aluminosilicate (Nicalon/CAS) cross-ply [0/90]_2S ceramic matrix composite at elevated temperatures under tension-tension fatigue loading. Tension-tension fatigue tests were performed with a load ratio of R = 0.10 and a frequency of 10 Hertz at 700°C and 850°C. These results were compared to results from a previous study conducted at room temperature. Material behavior and damage was recorded by fatigue life curves, elastic modulus' maximum and minimum strain, acetate replication techniques, and post-mortem fractography. Analysis of these results showed identical matrix dominated damage behavior at RT and 700°C. Ultimate …

A Study Of Graphite Peek Composite With Central Elliptical Holes Under Tension, Bill J. Lau

Theses and Dissertations

This study investigated the stress-strain response and failure modes of Graphite/Polyetheretherketone (Gr/PEEK) tension specimens containing a central elliptical hole. Both experiments and finite element numerical analyses were conducted. Test specimens included seven layups and three hole geometries; three of each combination were tested. The holes consisted of an ellipse with major axis aligned with the load axis, an ellipse with major axis transverse to the load axis, and a circle. Strain gages were located adjacent to the hole and midway between the hole and tab on all specimens. Strain data was used to plot stress-strain response. The analysis utilized a …

Characterization Of Fatigue Damage In A Metal Matrix Composite (Scs-6/ Ti-15-3) At Elevated Temperature, Brian P. Sanders

Theses and Dissertations

The fatigue characteristics of a unidirectional titanium based metal matrix composite (MMC) were investigated at elevated temperature (427°C). A hybrid strain controlled loading mode was used to subject the 0° and 90° laminas to fatigue. Along with the fatigue tests, microscopy and analytical modeling ware also conducted. This combination of activities led to defining the initiation and progression of damage and deformation in the MMC. Hen loading was parallel to the fiber on, the fatigue behavior was initially dominated by creep deformation of the matrix. Then, depending on the maximum strain, specimen failure was the result either fiber fractures or …

Electrorheological Fluids And Their Application In Automotive Clutches: Design Procedures And Recommendations, Ihab Fahmy

Archived Theses and Dissertations

No abstract provided.

Behavior Of Concrete Masonry Prisms Under Axial Compression, Tarek Ghoneim Mohamed Ghoneim

Archived Theses and Dissertations

No abstract provided.

Simulation Of Vertical Tail Buffet In Internal Vortex Breakdown Flows, Mark William Flanagan

Mechanical & Aerospace Engineering Theses & Dissertations

Computational simulation of vertical tail buffet in an internal vortex breakdown flow is considered. The fiuid-flow problem is formulated using the full, compressible, unsteady Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite volume scheme. The fluid-flow problem is solved in a configured circular duct using quasi-axisymmetric assumptions to simplify the flow equations. A plate is placed transverse to the incoming flow. Solution of the flow in the duct is performed with and without a rigid plate, and with and without an elastic plate. The elastic response of the plate is calculated assuming that it is a cantilever …

A New Adjoint Variable Method For The Sensitivity Analysis Of Dynamic Responses, Krishnamoorthy Ramesh

Mechanical & Aerospace Engineering Theses & Dissertations

A new adjoint variable method has been formulated for finding the sensitivity derivatives of dynamic system responses. Though the method can be based on any step-by-step time marching scheme, the Wilson Theta Method has been chosen as the basis of the new formulation . Wilson Theta Method is an implicit numerical integration scheme for finding the dynamic system responses. The new formulation uses the differential form of equations of motion as given by the Wilson Theta Method in its formulation of the adjoint equation. The conventional methods used for finding the sensitivity derivatives, namely, the direct differentiation technique, the central …

Optimum Design For Spring With Orthogonal Design Method, Han Fu - Jie

Tanzania Journal of Engineering and Technology (TJET)

Orthogonal design method is a sort of direct optimum method, by which the op- timal result may be obtained through simple computation and analysis. This method has gained increasingly extensive interest in scientific research, engineering design, end production management as well. The orthogonal table is the basic instrument for carrying out optimum design with orthogonal design method. It is a mathernatical table established On the basis Of the idea of isostatic distribution. As various levels may appear in any column, it makes a partial experiment contain levels of all factors furthermore. RII combina- tions of any two columns may appear …

Evaluation Of Dynamic Stresses And Fatigue Life Prediction For Randomly Loaded Structure, Walied Ahmed Moussa

Archived Theses and Dissertations

No abstract provided.