Mechanical Engineering Commons^™

Transition From Laminar To Turbulent Flow Around An Airfoil, Chang-Ren Chen

Doctoral Dissertations

"A computational fluid dynamics (CFD) code has been developed for two-dimensional incompressible turbulent flows and employed to solve the Navier Stokes equations around an airfoil of arbitrary shape. A low-Reynolds-number k — e turbulence model including curvature effect was used to consider the gain and loss of turbulent kinetic energy. To include laminar sublayer into the computational domain, a multi-layer grid and a cubic-slpine grid were introduced through a conservative form of coordinate transformation. The flow structure varies with the Reynolds numbers. For an airfoil at low Reynolds numbers (below ten thousand), distinct vortex shedding patterns can be found in …

Applications Of Finite And Wave Envelope Element Approximations To Acoustic Radiation From Turbofan Engine Inlets In Flight, A. V. Parrett

Doctoral Dissertations

"The problem of acoustic radiation from turbofan engine inlets in flow has not lent itself fully to analysis by numerical means because of the large domains and high frequencies involved. This project has extended the use of finite elements and wave envelope elements, elements which simulate decay and wavelike behaviour in their interpolation functions, from the no-flow case in which they have been proven, to cases incorporating mean flow. By employing an irrotational mean flow assumption, the acoustics problem has been posed in an axisymmetric formulation in terms of acoustic velocity potential, thus minimising computer solution storage requirements. The wave …

Bit Penetration Into Rock - A Finite Element Study, Jaw-Kuang Wang

Doctoral Dissertations

"A finite element approach has been developed to simulate bit penetration from bit-rock interaction to chip formation. A mathematical rock failure model, based on a review of the existing literature on rock tests, has been proposed to represent post-failure rock behavior and applied in the penetration simulations. The finite element program has been developed for two dimensional plane strain problems with non-linear material properties, geometrical nonlinearities and fracture. An anisotropic element as well as variable stiffness and stress release methods have been used. An iteration method, using an incremental approach, has been applied for continuous penetration and modifications of material …

Development Of Helicopter Flight Path Models Utilizing Modern Control Techniques, Alfred Fermelia

Doctoral Dissertations

"The nonlinear set of equations which represents helicopter motion are linearized about a prescribed nominal state. Once the linearized system is obtained it is validated by comparing the output of the nonlinear system to that of its linearized counterpart. Having obtained a linear model, linear system theory may then be applied in order to investigate the stability and control characteristics of the aircraft.

General techniques for simulating helicopter pilot response for inclusion in a flight path simulation program have been devised. To provide the desired flight goal, a nominal flight trajectory is obtained from an existing nonlinear model. With this …

Influence Of Initial Turbulence Intensity On The Heat And Moisture Transfer Through A Recirculated Air Curtain, Nguyen Quang Van

Doctoral Dissertations

"An air curtain is a directed jet of air separating a controlled space from an environment of different temperature and humidity. This investigation describes the development and verification of an eddy viscosity model which accounts for the influence of the initial turbulence intensity on the transfer of heat and moisture across a recirculated air curtain. The control of the turbulence intensity at the nozzle exit of an air curtain permits control of heat and moisture transfer and therefore the energy required to operate the air curtain.

Both theoretical and experimental studies were made of the recirculated air curtain. An explicit …

The Effect Of Contact Angle, Surface Roughness, And Adsorption Of Heterogeneous Nucleation Of Condensing Water, Prafulla Chandra Mahata

Doctoral Dissertations

"Condensation of water vapor on various surfaces was studied experimentally. It was found that supersaturations as high as 25% were required to initiate condensation on hydrophobic surfaces. The supersaturation data agreed qualitatively with the Volmer theory of heterogeneous nucleation. The influence of adsorption of water vapor was found to be small. Surface roughness caused a little reduction in the critical supersaturation"--Abstract, page iii.

Measurements Of Condensation Coefficient Exhibited By Water Drops Grown On Rural Cloud Nuclei, Abbas M. Sinnarwalla

Doctoral Dissertations

"Values of condensation coefficient, ß, were experimentally determined for water drops grown on cloud nuclei in atmospheric air samples. The measured quantities were supersaturation, final drop size (6 to 7.5 µm radius), and time to grow from near dry radius to final radius. The drops were grown in a vertical-flow thermal diffusion chamber, at supersaturations near 0.5 and 1.0%. The final drop sizes were large enough so that ß did not depend upon the size of the nucleus producing a given drop. The average value of ß was 0.025 with a standard deviation of about 0.01"--Abstract, page 2.

A Finite Element Method For Three-Dimensional Analysis Of Metal Forming, Nguyen Don Phu

Doctoral Dissertations

"The importance of metal forming by extrusion was reviewed. A Finite Element Approach was developed to analyze extrusion processes. A brick type linear element and the Upper Bound theorem were used to analyze the extrusion of a cylindrical billet into a square cross-section prism. A minimization technique for a non-linear functional with linear constraints was developed. Different types of boundary conditions were also formulated. A frictionless extrusion was simulated using the computer program developed. Velocity profiles at different sections of the deforming solid were obtained and an average extrusion pressure was predicted for a given area reduction ratio.

Extrusions from …

Numerical Modeling Of The Early Stage Of Cloud Formation In A Simulation Chamber, Adel Nassif Saad

Doctoral Dissertations

"A numerical model has been developed to simulate the growth of cloud droplets by condensation upon a spectrum of hygroscopic nuclei. The model is applicable to cloud simulation chamber conditions as well as to the study of the role of these nuclei on cloud base microstructure.

Equations are given for the growth by condensation of water vapor on a population of hygroscopic nuclei in a volume being cooled by expansion. The equations are integrated simultaneously, using Hamming's modified predictor-corrector method for given initial conditions, to obtain the droplet size distribution, temperature, pressure, supersaturation, and liquid water content. Temperature fluctuations, sedimentation …

An Analytical And Experimental Study Of The Dynamic Response Of A Press, Woosoon Bai

Doctoral Dissertations

"This dissertation presents a simplified mathematical model and computer simulation of the vertical motion of a press. The model is verified by comparing simulation results with actual field measurements.

Using this model, the computer simulation is then extended to study the dynamic response of a bolted press, one with loosened anchor bolts, and one which is isolated. Press performance, in terms of acceleration of the press, velocity of its foundation, and forces transmitted to the foundation, is analyzed in relation to the foundation mass and the stiffness of the isolators, where applicable. Comparative performances of the presses secured by the …

Direct And Inverse Heat Conduction In Rock Materials Using The Finite Element Method, Vernon Dale Allen

Doctoral Dissertations

"A finite element method is presented for solution of direct and inverse heat conduction problems in rock materials. Finite element programs for direct and inverse heat conduction problems were developed and demonstrated. Flow charts are given for the finite element programs.

The direct finite element heat conduction program changes material properties with temperature to approximate the temperature dependent properties of rock materials. An example problem was solved by the finite element method and also using Kirchoff's transformation. The finite element solution compared quite well with the Kirchoff transformation solution.

The inverse method utilizes the direct finite element heat conduction program …

Dropwise Condensation As Affected By Vapor Diffusion And Molecular Sticking, Salil K. Banerjee

Doctoral Dissertations

"Experimental values of heat flux in dropwise condensation on a gold plated vertical copper surface were determined in presence and absence of (or minute traces of) noncondensable gas. The noncondensable gas concentration varied from 0.0045% to 7.5% over a range of subcooling from 2.155 to 17.13°F and system pressure of 4.124 to 16.67 psia. The calculated heat transfer coefficient ranged from 1,545 to 11,135 Btu/hr-ft²-°F. In the part of the experiment where precautions were taken to avoid the presence of noncondensable gas in the water vapor, much higher values of heat flux were observed. Values of heat transfer coefficient ranging …

Solid-Fluid Drag Reduction, Ian Radin

Doctoral Dissertations

"Pressure drop measurements were made on a variety of solid-liquid suspension systems in order to study the effects of particle shape and size, concentration, fluid viscosity and tube diameter on drag reduction. Measurements were made over a wide range of Reynolds numbers in two tubes: 1/4 inch and 1 inch in diameter.

Drag reduction could always be obtained with fibrous additives of length-to-diameter ratio greater than 25-35 if the concentration was sufficiently high. The drag reduction behavior of these suspensions is different from that of high polymer and soap solutions. Laminar flow behavior is stabilized giving lower than normal friction …

Rock Fragmentation By Subsurface Thermal Inclusions - A Finite Element Study, Mahendrakumar Ramkrishna Patel

Doctoral Dissertations

"Although rock tunneling machines are being used extensively with performance and cost advantages over traditional drill and blast methods, their usefulness for hard rock excavation is far from being practical due mainly to the inability of present day mechanical cutters to penetrate these rocks economically. Among various novel techniques that are being investigated, internal heating methods seem to be the most promising. This investigation is concerned with a feasibility study of thermal rock fragmentation using heat to create in-depth thermal inclusions.

The three-dimensional problem of in situ rock fragmentation involves parallel rows of equidistant holes drilled to a constant depth. …

Hydrostatic Extrusion Of Waste Glass And Plastic, Subhash Govind Kelkar

Doctoral Dissertations

"Waste glass and waste plastic combine to form a major portion of nonbiodegradable, solid waste. These waste products aggravate the already too serious problem of environmental pollution. Hence, a means is sought of utilizing this waste in the construction industry, thus solving two problems simultaneously - that of beautifying the environment, and of procuring inexpensive building materials.

Extrusion is not an uncommon process as far as the manufacture of original products is concerned. Hydrostatic extrusion is a modification of the process wherein a billet or slug of some material is forced to flow through a die under the influence of …

Transient State Analysis Of Separated Flow Around A Sphere, Ching-Liang Lin

Doctoral Dissertations

"Transient state solution of the Navier Stokes equation was obtained for incompressible flow around a sphere accelerating from zero initial velocity to its terminal free falling velocity. By assuming rotational symmetry around the axis in the falling direction, the Navier Stokes equation and the continuity equation were simplified in terms of vorticity and stream function. The instantaneous acceleration of the falling sphere was calculated by considering the difference between the gravitational force and the drag force in a transient state. The governing partial differential equations were non-dimensionalized. A set of implicit finite difference equations was developed. In order to obtain …

Stability Of The Developing Laminar Flow In A Circular Tube, Lung-Mau Huang

Doctoral Dissertations

"An investigation is made of the linear stability of the developing laminar flow of an incompressible fluid in the entrance region of a circular tube. Both axisymmetric and non-axisymmetric small disturbances are considered in the analysis. The stability characteristics of the fully developed flow are also re-examined. The main flow velocity distribution used in the stability analysis is that from the solution of the linearized momentum equation. The governing equations for the disturbances and the boundary conditions constitute an eigenvalue problem which is solved by a direct numerical integration scheme along with an iteration technique. The solution starts with a …

Methods For Predicting The Influence Of Intense Sound, Steady Flow, And Elevated Temperature On The Acoustic Performance Of Automotive Exhaust System Components, Richard Chuka Oboka

Doctoral Dissertations

"The principal objective of this investigation was to study the feasibility of developing laboratory techniques for automobile-exhaust muffler design in order to reduce the amount of on-vehicle trial-and-error testing currently required. The investigation included (1) improving the capability of existing laboratory equipment to simulate the conditions in automobile exhaust (i.e., high-amplitude pressure waves, steady flow, and elevated temperature), and (2) theoretical and experimental studies of typical acoustic elements (side-branch resonators, expansion chambers, louvered tubes) used in muffler design. The sound fields used for these studies included pure tones, single pulses (tone bursts), random noise, and simulated automobile exhaust noise.

Empirical …

The Effects Of High Pressure And Temperature Environments On The Properties Of 6061-T651 Aluminum, Patrick George Davidson

Doctoral Dissertations

"During this experimental testing program the effects of the simultaneous application of high pressure and temperature environments on the mechanical properties of 6061-T651 aluminum were analyzed. From the data obtained at the yield and ultimate points a yield and ultimate model was developed based upon the parameters effective stress, effective strain, and the hydrostatic component of stress. This model was obtained solely from the data acquired from uniaxial tensile specimen tested at various pressures and temperatures. Two other loading paths--biaxial tension and torsion--were then used to verify the accuracy of the model. From the testing program, data were also obtained …

Linear Stability Of Non-Parallel Flow In The Entrance Region Of Ducts, Francis Chung-Ti Shen

Doctoral Dissertations

"An investigation is made of the linear stability of the developing flow of an incompressible fluid in the entrance region of annular ducts, circular tubes, and parallel-plate channels. Small axisymmetric disturbances for annular duct and tube flows and small two-dimensional disturbances for channel flow are considered in the analysis. In formulating the stability problems, account is taken of the transverse velocity component of the mainflow. This results in the modified Orr-Sommerfeld equations, one for annular duct and tube flows and the other for channel flow. The mainflow velocity fields utilized in the stability analysis are those from the solutions of …

Numerical Simulation Of Heat, Mass, And Momentum Transfer In An Atmospheric Boundary Layer, Darrell W. Pepper

Doctoral Dissertations

"Considerable interest has developed in recent years to understand transport phenomena in thermally stratified boundary layers. More complete knowledge in this field is needed to improve the prediction of the diffusion of air pollutants in the lower atmosphere as well as in forecasting air-water circulation for weather conditions.

The atmospheric boundary layer is modeled using the equations of continuity, momentum, energy, and concentration. Closure of this set of partial differential equations is hindered by the turbulence terms. Using turbulence kinetic energy, the system of equations is closed by internally determining the exchange coefficients of heat, mass, and momentum along with …

A Study Of The Dynamic Loading Of Hydrodynamically Lubricated Journal Bearings, Nader Khorzad

Doctoral Dissertations

"The analytical and experimental investigation presented here examined the response of a full journal bearing to a unidirectional dynamic load. Frequency response of the bearing at different eccentricity ratios was investigated. It was concluded that the response of the bearing varies with eccentricity. The experimental data obtained was compared to an analytical model which considered inertial, damping, and elastic characteristics of the lubricant film. An investigation of film pressure revealed that the pressure due to journal center acceleration is smaller than the hydrodynamic and squeeze-film pressures"--Abstract, page 1.

A Yield And Fracture Model For Ti-6al-4v Titanium And 7075-T6 Aluminum, Richard L. Pendleton

Doctoral Dissertations

"The objective of the research being reported in this thesis was to conduct a series of experiments on two commonly used structural metals in several different environmental pressures so that a graphical representation of the material response both to yielding and fracture could be ascertained. It was further intended to show that parameters herein defined and called effective stress, effective strain, and pressure are useful parameters for graphically representing the material response. The final goal of this research was to show that the graphical representation does, in fact, predict the yield and fracture for a simple forming process. The forming …

The Application Of Impact Dampers To Continuous Systems, Ranjit Kumar Roy

Doctoral Dissertations

"A study has been made of the application of impact dampers to two types of continuous systems, a simply supported and a clamped beam. Previous efforts have included the effect of impact dampers on single degree of freedom and other systems with finite numbers of degrees of freedom.

Experimental models were tested in the laboratory and finite element computer programs were developed to calculate response. Results from calculations agree favorably with experimental tests. Further, results from the first few natural modes also compare reasonably with data published on systems with finite number of degrees of freedom.

Curves are presented which …

Methods And Applications Of Systems Identification, Allen Glenn Behring

Doctoral Dissertations

"A "Schmidt filter" is proposed to compute an optimal orthonormal basis for a set of "noisy" filter input functions. Procedures for determining the transfer function and inverse transfer function of the filter are given. The Schmidt filter is applied to the problem of determining mathematical models of discrete, stationary, linear, dynamic systems for the case where measurements may be corrupted by noise of unknown statistics. The identification problem is reconsidered for the case where noise and signal moments are specified. Procedures are given which insure unbiased, adaptive estimates of system order and parameters for this case. These theoretical propositions are …

An Exact Analysis Of Two-Dimensional Radiative Transfer In An Absorbing And Emitting Gray Medium, William F. Breig

Doctoral Dissertations

"The exact formulations for the radiative flux and the emissive power are presented for a two-dimensional, finite, planar, absorbing and emitting, gray medium in radiative equilibrium. Exact expressions are obtained for the medium subjected to the following types of boundary conditions: (1) cosine varying diffuse, (2) cosine varying collimated, (3) constant temperature strip, and (4) the strip illuminated by a uniform collimated flux. The solutions for the physically unrealistic cosine varying models are used to construct the solutions for the more practical finite strip models. The two-dimensional equations are reduced to one-dimensional equations by the method of separation of variables. …

An Analytical Study Of A Confined Viscous Vortex, David Edward Crow

Doctoral Dissertations

"A composite solution for the flow field of a three dimensional, incompressible laminar, viscous vortex confined inside a conical converging nozzle is presented. This model is used to study the strong mainstream boundary layer interaction that occurs in confined vortex flows. The confined vortex flow field is divided into mainstream and boundary layer regions. A particular class of solutions of the general equations of motion is used to represent the vortex flow in the mainstream region. That is, the tangential velocity in the mainstream region is assumed to be of the form W = T(e)/R. Velocity and pressure profiles from …

Modal Truncation Of Substructures Used In Vibration Analysis, Suresh Kumar Tolani

Doctoral Dissertations

"The objective of this study is to describe in a unified manner a group of structural dynamics analyses using the substructures technique. An additional effort is to provide a consistent basis for the selection of substructure principal modes as required by this method. Substructure principal mode frequency roots and strain energy are two criteria evaluated for the selection of substructure principal modes. System eigenvalues and system strain energy are investigated for the comparison of results in the principal modes. System strain energy should provide more rational results since it is proportional to the stress times the strain in the system …

Determination Of Thermal Contact Resistance Between Metals Using A Pulse Technique, William Edward Stewart Jr.

Doctoral Dissertations

"This dissertation reports the results of an experimental and analytical investigation to determine the thermal contact resistance of several metal specimen pairs using a relatively new pulse technique. Metal specimens were aluminum 2024-T3, aluminum 6061-T6, aluminum 7075-T6, copper 110, stainless steel 304, molybdenum, and Armco iron. Thermal contact resistance was also determined for dissimilar metal specimen pairs of aluminum 6061-T6 - copper 110 and aluminum 7075-T6 - copper 110. Aluminum 7075-T6, copper 110, and stainless steel 304 specimens were tested to determine the variance of contact resistance with time after loading.

Specimens were circular cylindrical disks between .033 and .061 …

An Experimental Investigation Of The Effects Of Ambient And Heated Steady Flow And Intense Sound Levels On The Response Of Acoustic Filter Elements, Raymond H. Schaffart

Doctoral Dissertations

"The primary purpose of this research was to investigate the effects of flow and finite amplitude waves on the response of acoustic elements. A further purpose was to evaluate the effects of elevated temperatures and cross-sectional dimensions on element performance. As an integral part of this work various laboratory techniques were explored for their suitability.

Empirical models for the acoustic impedance of side branch resonators were developed for the two operational modes, i.e., flow past the resonator and finite amplitude wave inputs. A description of the complex variation of the acoustic resistance of the resonator with flow past and variable …