Mechanical Engineering Commons^™

Investigation Of Flow Phenomena In A Repetitively-Pulsed Gas Flow Switch, Shivakumar Srinivasan

Mechanical & Aerospace Engineering Theses & Dissertations

A two-dimensional, unsteady numerical model for analyzing the characteristics of gas flowing through a gas blown spark gap switch has been developed. The computational model is governed by the conservation equations of mass, momentum and energy in an inviscid, non-conducting, perfect, compressible fluid. The governing equations have been solved by using MacCormack's finite volume technique. The effects of rapid gas heating and subsequent changes in the fluid properties of the gas are examined in the high-pressure spark gap switch. The gas temperature, expansion velocity, density and pressure are calculated as functions of time. Air is the dielectric flowing through the …

Studies On The Interference Of Wings And Propeller Slipstreams, Ramadas K. Prabhu

Mechanical & Aerospace Engineering Theses & Dissertations

The small disturbance potential flow theory is applied to determine the lift of an airfoil in a nonuniform parallel stream. The given stream is replaced by an equivalent stream with a certain number of velocity discontinuities, and the influence of these discontinuities is obtained by the method of images. Next, this method is extended to the problem of an airfoil in a nonuniform stream of smooth velocity profile. This model allows perturbation velocity potential in a rotational undisturbed stream. A comparison of these results with numerical solutions of Euler equations indicates that, although approximate, the present method provides useful information …

Combined Forced And Free Convection In The Trombe Wall Channel, Jim Ginchaun Huang

Mechanical & Aerospace Engineering Theses & Dissertations

A vertical channel connected by horizontal exit and entrance segments is simulated and represents a flow passage for a Trombe wall solar collector. The two-dimensional combined forced and free convection mode is investigated for the laminar regime. The vertical walls of the channel are maintained at a constant but different temperature while horizontal walls are insulated. A finite difference method using up-wind differencing for the non-linear convective terms and central differencing for the second order derivatives is employed to solve the governing differential equations for mass, momentum, and energy balances. The solution is obtained for stream function, vorticity, and temperature …

Shape Optimization For Elastic Hollow Bars In Torsion, Jahau Lewis Chen

Mechanical & Aerospace Engineering Theses & Dissertations

The problem of finding optimal cross-sectional shapes of elastic hollow bars in torsion is formulated and solved numerically. A variational formulation for the state equation is presented, and the material derivative of continuum mechanics is used for the shape design sensitivity analysis. Performance criteria include the bending stiffness, the torsional rigidity, and the weight of the bar. The existence of a keyway, an example of geometric irregularity, can be considered as well. The material can be either isotropic or anisotropic. The finite element method is used for the numerical solution of the variational state equation and is integrated into an …

Design Of A Combustion System Simulating Waste Heat Recovery From Diesel Engine Exhaust Gases, Nikolaos Papadopoulos

Mechanical & Aerospace Engineering Theses & Dissertations

A forced-draft laboratory combustion system simulating diesel engine exhaust gas volume flow rate and temperature conditions for waste energy recovery is analyzed and discussed. The system consists of a fan which supplies the air. The slightly compressed air is then ducted through a combustor where it is heated, and then to an air-quencher where it is cooled to a desired temperature. Finally, the air is sent through a heat exchanger, after a diffuser process, for waste heat recovery.

A gas dynamic analysis has been performed for each component part as well as a parametric study via a computer program in …

Comparative Heat Load Analysis For A Direct Gain Passive Solar Building, Hong Hu

Mechanical & Aerospace Engineering Theses & Dissertations

A newly erected University Police Safety Building on the campus was constructed with passive solar design features. The slab-on-grade brick building has 3081 square feet of conditioned space, an ample south-facing solar aperture with clerestory and an air-to-air heat pump system. A comparative winter heat load assessment has been made in order to determine the fraction of the heat load which can be met by the winter sun (Norfolk, VA 37°N Latitude), and more importantly to probe differences which result when various heat load estimating methods are employed. Techniques employed included the degree day method·, bin method with and with …

The Development Of A Microprocessor Controlled Linearly Actuated Valve Assembly, Raymond H. Wall

Mechanical & Aerospace Engineering Theses & Dissertations

The development of a proportional fluid control valve/assembly is presented. This electro-mechanical system is needed for space applications to replace the current proportional flow controllers that use bulky hydraulic or pneumatic actuation systems. The flow is controlled by a microprocessor system that monitors the control parameters of upstream pressure and requested volumetric flow rate. The microprocessor achieves the ·proper valve stem displacement by means of a digital linear actuator. A linear displacement sensor is used to measure the valve stem position. 'Ibis displacement is monitored by the microprocessor system as a feedback signal to close the control loop. With an …

An Analytical Design Procedure For The Determination Of Effective Leading Edge Extensions On Thick Delta Wings, Farhad Ghaffari

Mechanical & Aerospace Engineering Theses & Dissertations

An analyt1cal des1gn procedure for Lead1ng-Edge Extensions (LEE) has been developed for thick delta wings. This LFE device is des1gned to be mounted to a w1ng along the pseudo-stagnation stream surface associated w1th the attached flow design lift coeff1cient of greater than zero. The intended purpose of the device is to improve the aerodynamic performance of high subsonic and low super son1c aircraft at incidences above that of attached flow design lift coefficient, by us1ng a vortex system emanating along the leading edges of the device. The low pressure assoc1ated with these vort1ces would act on the LEE upper surface …

Underwater Acoustic Wavefront Phase Fluctuations, George L. Vojtech Jr.

OES Theses and Dissertations

In conventional underwater acoustics sound propagation is generally modeled and applied as a coherent or incoherent process. This paper addresses a relatively new theory, that of a range driven increasingly incoherent ray propagation through a real ocean environment, Possible mechanisms are discussed and experimental data presented to reinforce the theory.

Experiments On Melting Around An Isothermal Horizontal Cylinder Under Computer Control, Timothy Moore Rothgeb

Mechanical & Aerospace Engineering Theses & Dissertations

The melting of a solid around an isothermal horizontal cylinder is a physical phenomenon which must be understood when attempting to design a latent heat storage system. The desire to design such a system is the motivating factor in this research. To gain this understanding of the fundamental melting processes several experiments were designed, and two sets of Stefan and Rayleigh number experiments were undertaken. Experiments were also performed to determine the properties of the paraffin that was used in these investigations. During the investigations of the melting processes, the temperature was measured at several locations throughout the liquid and …

Effect Of Transducer Size On The Statistical Properties Of A Simulated Turbulent Wall Pressure Field, Mehdi R. Khorrami

Mechanical & Aerospace Engineering Theses & Dissertations

The root mean square pressure was calculated with synthetically generated pressure signals for transducers of different size. The transducer diameters were in the range of 0.02 < _s*of 12,250. The lower limit of the diameter simulated here was much smaller than diameters reported previously by other workers. Calculated root mean square pressure levels developed in the present work were in good agreement with the measured experimental data.

In order to check the simulated pressure signals, the power spectrum and two point correlation were calculated as well. The power spectra obtained with the smaller transducers were higher in energy level at …

Viscous Modeling And Computation Of Leading-And Trailing-Edge Vortex Cores Of Delta Wings, Balakrishnan Lakshmanan

Mechanical & Aerospace Engineering Theses & Dissertations

A Finite-Difference method is presented for calculating steady quasi-axisymmetric flow of an incompressible fluid at large Reynolds number. Approximations of the boundary-layer type are employed to reduce the Navier-Stokes equations to a pair of non-linear parabolic equations. Along with the governing equations, initial conditions are specified at some upstream cross section and boundary conditions are specified at the axis of symmetry and on the outer bounding surface.

The governing equations are replaced by a set of quasilinear finite-difference equations. The solution is obtained by a marching technique, which proceeds step-by-step in the axial direction. At each axial station, an iterative …

On The Space Shuttle Wing Thermal-Structural Analysis, Kumar Krishna Tamma

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element approach for efficient thermal-structural analysis of structures with thermal protection systems (TPS) is described. The approach is applied to Space Shuttle wing structure configurations subjected to reentry heating. New two and three-dimensional finite elements are developed to model heat transfer in the TPS and supporting structure. A typical TPS/Structural element predicts transient nonlinear temperature variations through the TPS thickness and detailed structural temperatures at the TPS/Structure interface. The accuracy of the TPS/Structure approach in two and three-dimensions is evaluated by comparisons with the conventional approach for various configurations of the wing structure. The results indicate that the …

Application Of The Method Of Lines For Solutions Of The Navier-Stokes Equations Using A Nonuniform Grid Distribution, Jamshid Samareh Abolhassani

Mechanical & Aerospace Engineering Theses & Dissertations

The feasibility of the method of lines is investigated for solutions of physical problems requiring nonuniform grid distributions. To attain this, it was also necessary to investigate the stiffness characteristics of the pertinent equations. For specific applications, the governing equations considered are those for viscous, incompressible, two-dimensional and axisymmetric flows. These equations are transform­ ed from the physical domain having a variable mesh to a computational domain with a uniform mesh. The two governing partial differential equations are the vorticity and stream function equations. The method of lines is used to solve the vorticity equation and the successive over relaxation …

Stability Analysis Of Closed Surge Tanks By Phase-Plane Method, Mostafa A. Sabbah

Civil & Environmental Engineering Theses & Dissertations

The governing equations describing water level oscillations in a closed surge tank with compressed air at the top of the tank are a set of nonlinear ordinary differential equations if the hydraulic system is analyzed as a lumped system. These oscillations are stable or unstable depending on the parameters of the plant and the type and magnitude of the disturbance.

The present available stability criterion has been developed by linearizing the governing equations and is, therefore, valid only for small disturbances.

In the research reported herein, the governing equations are normalized to reduce the number of parameters from nine to …

Application Of Least-Squares Method To The Determination Of Orthotropic Elastic And Photoelastic Constants, R. G. Chermahini

Mechanical & Aerospace Engineering Theses & Dissertations

A least-squares technique is developed in matrix form to determine orthotropic elastic and photoelastic constants. Orthotropic elastic constants are determined by mounting strain gages on a half-plane specimen which is subjected to a compressive concentrated force. Strain values corresponding to a 1000 lb load and coordinates of the points where the gages are located are used as input data to the governing equation of orthotropic elasticity for the model under consideration. Orthotropic photoelastic constants are determined using a transparent composite half-plane model which is subjected to a concentrated load. Photoelastic constants are determined using the coordinates of selected point on …

Interaction Of A Two-Dimensional Transverse Jet With A Supersonic Mainstream, Gilbert Otto Kraemer

Mechanical & Aerospace Engineering Theses & Dissertations

A experimental investigation of the interaction of a twodimensional sonic jet injected transversely into a confined main flow has been conducted. The main flow consisted of air at a Mach number of 2.9. The effects of varying the jet parameters on the flow field were examined using surface pressure and composition data. Also, the downstream flow field was examined using static pressure, pitot pressure, and composition profile data. The jet parameters varied were gapwidth, jet static pressure, and injectant species of either helium or nitrogen. The values of the jet parameters used were 0.039, 0.056,and 0.109 cm for the gapwidth …

Calculation Of Potential Flow Past Non-Lifting Bodies At Angle Of Attack Using Axial And Surface Singularity Methods, Jin-Yea Shu

Mechanical & Aerospace Engineering Theses & Dissertations

Two different singularity methods have been utilized to calculate the potential flow past a three dimensional non-lifting body. Two separate FORTRAN computer programs have been developed to implement these theoretical models, which will in the future allow inclusion of the fuselage effect in a pair of existing subcritical wing design computer programs.

The first method uses higher order axial singularity distributions to model axisymmetric bodies of revolution in an either axial or inclined uniform potential flow. Use of inset of the singularity line away from the body for blunt noses, and cosine-type element distributions have been applied to obtain the …

Improved Finite Element Methodology For Integrated Thermal-Structural Analysis, Pramote Dechaumphai

Mechanical & Aerospace Engineering Theses & Dissertations

An integrated thermal-structural finite element approach for efficient coupling of thermal and structural analysis is presented. New thermal finite elements which yield exact nodal and element temperatures for one-dimensional linear steady-state heat transfer problems are developed. A nodeless variable formulation is used to establish improved thermal finite elements for one-dimensional nonlinear transient and two-dimensional linear transient heat transfer problems. The thermal finite elements provide detailed temperature distributions without using additional element nodes and permit a common discretization with lower order congruent structural finite elements. The accuracy of the integrated approach is evaluated by comparisons with analytical solutions and conventional finite …

Experimental Investigation Of A Direct Expansion Solar-Assisted Heat Pump, James Yau-Jwo Shen

Mechanical & Aerospace Engineering Theses & Dissertations

A direct expansion solar-assisted heat pump, which uses economical bare solar collectors as evaporator, is designed and operated. The experimental results indicate that marked improvement in thermal performance results if the collector/ evaporator temperature is maintained at o0c to 10°c above the ambient temperature. During the course of this investigation, the system thermal performance is determined under various ambient and operating conditions by measuring the incident solar energy flux, refrigerant flow rate, temperature and pressure at various locations in the system. The heat pump coefficient of thermal performance and solar collector efficiency ranging from 2.0 to 3.0 and 40% to …

Water Wave Refraction With Non-Linear Theory, Im Sang Oh

OES Theses and Dissertations

Two different kinds of wave refraction models are formulated in the present study using Stokes' third order wave theory. One type of model is utilized in a parametric study employing several different topographies. Wave trajectories obtained from this model, when obtained by using first and third order wave theory with and without the consideration of energy dissipation, show considerable differences. These differences are examined in more detail for a bottom of constant slope: (1) An approximate 10% difference occurs between the refraction coefficients obtained using the first and the third order wave theory. (2) Considerably different ray trajectories are detected …

Analysis Of Aerothermodynamic Environment Of A Titan Aerocapture Vehicle, Hsing Chow

Mechanical & Aerospace Engineering Theses & Dissertations

The extent of convective and rad1ative heating for a Titan entry vehicle is invest1gated. The flow in the shock layer is assumed to be axisymmtric, steady, viscous, and compressible. It is further assumed that the gas is in chemical and local thermodynamic equilibrium and tangent slab approximation is used for the rad1ative transport. The effect of slip boundary conditions on the body surface and at the shock wave are included in the analysis of high altitude entry conditions. The implicit finite difference technique is used to .solve the viscous shock layer equations for a 45-degree sphere cone at zero angle …

Experimental Investigation Of A Rectangular Surface Thermal Plume, Li-Cheng Chu

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental investigation of the three dimensional mean temperature distribution of a rectangular buoyant surface thermal plume has been conducted for a range of buoyancies, velocity ratios, Reynolds numbers, and for various turbulence generating screens in the crossflow. This study has been motivated by a concern about the applicability of laboratory model data for predicting prototype plume behavior.

A large scale model has been built to study a buoyant, rectangular surface thermal plume which enters at right angles to a constant temperature uniform crossflow of depth equal to that of the plume. A large water tank and flume with weir …

Design And Analysis Of A Hybrid Thermoelectric Solar Collector, Kay Eddie Shaheen

Mechanical & Aerospace Engineering Theses & Dissertations

A conventional flat-plate collector is modified by imbedding thermoelectric power generators between the absorber plate and flow tubes in parallel finned-tube passes. As solar energy cascades through these generators a temperature differential between the hot and cold junctions of the device produces direct current electricity. Energy not converted to electric power is converted away for use in domestic space and/or water heating.

A parametric study is performed on the steady-state model via computer program in order to find values of design variables that maximize electric power production for purposes of driving pumps, fans, and ·controlling devices. The results of this …

Photoelastic Investigation Of Load Transfer In Eccentrically Loaded Single Lap Joints, Stephen Antrim Hann

Mechanical & Aerospace Engineering Theses & Dissertations

Photoelastic models of three eccentrically loaded single lap joints were analyzed. The adherends of each joint were identical and the bondlines differed in thickness and material properties. The adherends were analyzed for both cylindrical plate behavior and geometrical nonlinearity and the load transfer efficiency was examined. For all three models it was found that over 98% of the shank behaves as a cylindrical plate and that a geometrically nonlinear analysis yields bending stresses substantially lower than a linear analysis and that a relatively thick, low modulus bondline can increase load transfer efficiency.

Effects Of Multiple Scattering And Surface Albedo On The Photochemistry Of The Troposphere, Tommy Reinhold Robert Augustsson

Mechanical & Aerospace Engineering Theses & Dissertations

A one-dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families has been developed and used to investigate the vertical profiles and the natural (including atmospheric chemical reactions) and anthropogenic sources and sinks of these species. The species continuity equations are solved numerically applying prescribed boundary conditions. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. Heterogeneous losses (e.g. rainout, gas-to-particle chemistry, and dry deposition), are parameterized to make calculated profiles consistent with measurements. The photochemical model is coupled to a radiative transfer model that calculates the radiation …

Sound Absorption In N2-H2o Gas Mixtures At Room Temperature And Low Frequency/Pressure Ratios, William Axam Griffin

Mechanical & Aerospace Engineering Theses & Dissertations

This study was motivated by a need to obtain standard values of nitrogen's contribution to sound absorption in the Earth's atmosphere. Specific goals included accurate measurements of sound absorption in nitrogen - water vapor mixtures at room temperature and low frequency/pressure ratios, the determination of the N₂ vibrational relaxation peak location, (f/P)_max, on the f/P axis as a function of humidity, h, and critical evaluation of all results.

The free decay technique was used in a resonance tube to obtain ten sets of sound absorption data in N₂-H₂O gas mixtures and requisite companion …

Sound Absorption In N2-H2O Gas Mixtures At Elevated Temperatures, Roger W. Meredith

Physics Theses & Dissertations

Sound absorption measurements were conducted in N₂ -H₂O gas mixtures at 297, 343, and 387 Kelvin to determine the location of the vibrational relaxation peak of nitrogen on the frequency/pressure, (f/P), axis as a function of humidity and temperature. At low humidities the best fit of the data is to a linear relationship between (f/P)_max and humidity (h) yields a slope of 1 .84 X 10⁴ Hz/ atm mole fraction at all three temperatures. The slope is the same as that reported by Zuckerwar and Griffin (2.00 X 10⁴ Hz/atm mole fraction) but is …

Thermodynamic And System Performance Analysis Of A Heat Pump That Employs A Two-Phase Flow Collector As Evaporator, Yu-Fang Chiang

Mechanical & Aerospace Engineering Theses & Dissertations

A thermodynamic model is developed to analyze the thermal performance of two phase flow solar collectors, The well-known equilibrium homogeneous theory is used to model the two phase flow in the solar collectors. The resultant set of coupled ordinary differential equations for saturated pressure and quality of working fluids in the collector tubes are solved by an iterative procedure using a fourth order Runge-Kutta method. The results are then applied to determine the thermal performance of a solar assisted heat pump which uses two phase flow collector as the evaporator, The results indicate that even with the use of less …

Feasibility Of Quasi-Random Band Model In Evaluating Atmospheric Radiance, Navin Mirakhur

Mechanical & Aerospace Engineering Theses & Dissertations

The use of the quasi-random band model in evaluating the upwelling atmospheric radiation is investigated. The spectral transmittance and total band absorptance are evaluated for selected molecular bands by using the line-by-line model, quasi-random band model, exponential sum fit method, and empirical correlations, and these are compared with the available experimental results. The atmospheric transmittance and up­ welling radiance have been calculated by using the line-by-line and quasi-random models and are compared with the results of an existing program called LOWTRAN. The results obtained by the exponential sum fit and empirical relations are not in good agreement with experimental results …