Mechanical Engineering Commons^™

Topology And Grid Adaption For High-Speed Flow Computations, Jamshid Samareh Abolhassani

Mechanical & Aerospace Engineering Theses & Dissertations

This study investigates the effects of grid topology and grid adaption on numerical solutions of the Navier-Stokes equations. In the first part of this study, a general procedure is presented for computation of high-speed flow over complex three-dimensional configurations. This includes the grid generation and solution algorithm for Navier-Stokes equations in a general three-dimensional curvilinear coordinate system. The flow field is simulated on the surface of a Butler wing in a uniform stream. Results are presented for Mach number 3.5 and a Reynolds number of 2,000,000. The O-type and H-type grids have been used for this study, and the results …

Computation Of 2-D And 3-D Natural Convection Heat Transfer In Closed And Vented Cavities, T. O. Mohieldin

Mechanical & Aerospace Engineering Theses & Dissertations

The natural convective heat transfer in closed and vented cavities has been studied numerically, using the primitive variables formulation. A two-and three-dimensional enclosure, and a two-dimensional Trombe Wall channel geometries are considered. The flow has been assumed to remain Laminar, and Boussinesq approximation is invoked for solving the governing equations, The finite-difference method used in this study, is based on the SIMPLER algorithm which uses a combination of central and upwind differencing scheme to obtain stable numerical results.

For both geometries, namely the closed and vented cavities, the fundamental nature of the fluid dynamic and heat transfer characteristics is revealed …

Structural Sensitivity Analysis On A Parallel Computer, Niu Kian Teck

Civil & Environmental Engineering Theses & Dissertations

Substructuring formulation using adjoint variable approach has been developed for design sensitivity analysis and optimization of large scale structures. In this study, the procedure for statics and sensitivity analysis are re-examined to propose a programming scheme which can be implemented either in a sequential or parallel environment. The computational times of the substructuring formulation using a single processor versus multi-processors are compared to see the effectiveness of the formulation in the concurrent computing environment.

The Effects Of Nonlinear Damping On The Large Deflection Response Of Structures Subjected To Random Excitation, Chunchu Bhavani Prasad

Mechanical & Aerospace Engineering Theses & Dissertations

Effects of both nonlinear damping and large deflection stiffness are included in the theoretical analysis in an attempt to explain the experimental phenomena of aircraft panels excited at high sound pressure levels; that is the broadening of the strain response peak and the increase in modal frequency. Beams and symmetrically laminated plates subjected to acoustic excitation are considered in the analyses. The excitations are ergodic and Gaussian with zero mean. A polynomial containing both linear and nonlinear damping terms is considered as a damping model. Galerkin's method is used to derive modal equations. Direct equivalent linearization is used to solve …

A Numerical Study Of Three-Dimensional Vortex Breakdown, Robert Edward Spall

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical simulation of vortex breakdown using the time-dependent Navier-Stokes equations was performed. Unlike previous studies, the numerical algorithm, formulated in terms of the velocity and vorticity, was not restricted to axisymmetric flows. Prototype vortices were parameterized in terms of their Reynolds number and Rossby number. Two cases were studied extensively. In one case, a vortex was imbedded in a uniform free stream. In the other case, the axial velocity of the free stream was decelerated in the streamwise direction. For both cases breakdown occurred when the Rossby number was below a critical value. Vortex lines, particle traces and velocity …

Experimental Study Of Shock Wave Interference Heating On A Cylindrical Leading Edge, Allan R. Wieting

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet at Mach numbers of 6.3, 6.5, and 8.0 is presented. Stream Reynolds numbers ranged from 0.5 x 10⁶ to 4.9 x 10⁶ per foot and stream total temperature ranged from 2100 °R to 3400 °R. The model consisted of a 3-inch-diameter cylinder and a shock generation wedge articulated to angles of 10, 12.5, and 15 degrees. The primary goal of this study was to obtain a fundamental understanding of the fluid mechanics of shock wave …

Finite Element Methodology For Nonlinear Free And Harmonic Forced Vibrations Of Beam And Plate Structures, Kamolphan Decha-Umphai

Mechanical & Aerospace Engineering Theses & Dissertations

The literature and experiments have shown that nonlinear vibrations produce significant effects in structural analysis, especially the frequency-amplitude-force relation and the analysis of strain. An analysis was developed to predict both the frequency-amplitude-force relation and strains of beam and plate structures. Two finite element methods were developed, namely, the iterative single-mode method (method I) and the multiple-mode method (method II). The harmonic force matrix was developed to analyze nonlinear forced vibrations. Nonlinear free vibration was a special case of the general forced vibration by setting the harmonic force matrix equal to zero. The harmonic force matrix represents the external applied …

Coupled Bending-Torsion Steady-State Response Of Pretwisted, Nonuniform Rotating Beams Using A Transfer-Matrix Method, Carl E. Gray Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Using the Newtonian method, the equations of motion are developed for the coupled bending-torsion steady-state response of beams rotating at constant angular velocity in a fixed plane. The resulting equations are valid to first order strain-displacement relationships for a long beam with all other nonlinear terms retained. In addition, the equations are valid for beams with the mass centroidal axis offset (eccentric) from the elastic axis, nonuniform mass and section properties, and variable twist. The solution of these coupled, nonlinear, nonhomogeneous, differential equations is obtained by modifying a Hunter linear second-order transfer-matrix solution procedure to solve the nonlinear differential equations …

Calibration Of Old Dominion University Low-Speed Wind Tunnel, Nicolaos P. Sargianos

Mechanical & Aerospace Engineering Theses & Dissertations

No Abstract.

Chemoviscosity Modeling Of Thermosetting Resins, Jia-Mo Bai

Mechanical & Aerospace Engineering Theses & Dissertations

A new analytical model for simulating chemoviscosity of thermosetting resin has been formulated. The model is developed by modifying the well-established Williams-Landel-Ferry (WLF) theory in polymer rheology for thermoplastic materials. By introducing a relationship between the glass transition temperature Tg (t) and the degree of cure a(t) of the resin system under cure, the WLF theory can be modified to account for the factor of reaction time. Temperature-dependent functions of the modified WLF theory constants C₁(T) and C₂(T) were determined from the isothermal cure data. Theoretical predictions of the model for the resin under dynamic …

An Experimental And Analytical Investigation Of Incompressible Fluid Flow Through A Distensible Tube System, Steven C. Wells

Mechanical & Aerospace Engineering Theses & Dissertations

An analysis was made of pressure and flow in a novel elastic tube system which has been used to theorize certain aspects of renal hemodynamic cs. Validation of the theory could alter the treatment of certain heart and kidney disorders. In an attempt to better understand a system flow anomaly under steady driving head conditions, experiments were performed, and a mathematical model was developed. The development of the model incorporated a set of nonlinear differential and algebraic equations. Using a finite-difference analysis as the method for obtaining a numerical solution, various pressures and flows were obtained. Results for the steady-state …

Three-Dimensional Elastic-Plastic Finite Element Analysis Of Fatique Crack Growth And Closure, Rahmatollah G. Chermahini

Mechanical & Aerospace Engineering Theses & Dissertations

The purpose of this study was to develop a three-dimensional, elastic-plastic, finite element analysis to investigate crack extension and closure under cyclic loading. The initial study concentrated on the behavior of a straight through crack in a finite-thickness plate subjected to tensile loading (middle-crack tension specimen). The finite element model was composed of 8-noded (linear-strain) isoparametric elements. In the analysis, the material was assumed to be elastic-perfectly plastic. Zienkiewicz's "initial-stress" method, von Mises' yield criterion, and Drucker's normality condition, under small-strain assumptions, were used to account for plasticity. The three-dimensional analysis is capable of extending the crack and changing boundary …

An Analytical And Experimental Study Of Clearance And Bearing-Bypass Load Effects In Composite Bolted Joints, Rajiv Vikas Arun Naik

Mechanical & Aerospace Engineering Theses & Dissertations

A combined analytical and experimental study is conducted to determine the effects of clearance and bearing-bypass loading for mechanically fastened joints in composites. A simple method of analysis is developed to account for the nonlinear effects of bolt-hole clearance. The nonlinear load-contact variations for clearance-fit fasteners are also measured using specially instrumented fasteners. For a quasi-isotropic graphite/epoxy laminate, results show that the contact arc as well as the peak stresses around the hole and their locations are strongly influenced by the clearance. After a slight initial nonlinearity, the peak stresses vary linearly with applied load. The typical clearance levels are …

Convective Heat Transfer From Circular Cylinders Located Within Perforated Cylindrical Shrouds, Kamran Daryabeigi

Mechanical & Aerospace Engineering Theses & Dissertations

The influence of perforated cylindrical shrouds on the convective heat transfer to circular cylinders in transverse flow has been studied experimentally. Geometries studied were similar to those used in industrial platinum resistance thermometers. The influence of Reynolds number, ventilation factor (ratio of the open area to the total surface area of shroud), radius ratio (ratio of shroud's inside radius to bare cylinder's radius), and shroud orientation with respect to flow were studied.

The experiments showed that perforated shrouds with ventilation factors in the range 0.1 to 0.4 and radius ratios in the range 1.1 to 2.1 could enhance the convective …

An Investigation Of High Strength To Weight Corrugated Compression Panels With Non-Load Carrying Webs, Charles Thomas Lee Mills

Mechanical & Aerospace Engineering Theses & Dissertations

An investigation of the weight saving potential of corrugated compression panel concepts using curved elements and non-load carrying webs was performed. The concepts investigated were corrugated panels with flat and curved caps with beaded webs. These concepts utilize a beaded web that carries negligible axial load but is very stiff in the transverse direction. Therefore the web substantially stabilizes the load carrying caps to produce a high weight-strength efficient structure.

The optimum geometry parameters were determined using an iterative solution method employing simplified buckling assumptions. The results were checked with a non-linear optimization program coupled to a rigorous buckling analysis. …

Erosion Of Yellow Brass And Type 304 Stainless Steel In A Gas Blown Spark Gap, Rakasi Madhava Reddy

Mechanical & Aerospace Engineering Theses & Dissertations

Erosion rates of yellow brass and type 304 stainless steel electrodes were studied in air under pulse discharge conditions at a voltage of 100 kV, a current of 20 kA, and pulse durations of 70 ns. Anodes and cathodes, configured vertically, were fitted with removable hemispherical tips having a diameter of 0.95 cm and a mass of 3 gm. Tests were conducted inside a low speed, high pressure wind tunnel at pressures of 30 and 50 psig and air velocities ranging from 0 to 36 nm/s.

Erosion was studied gravimetrically for several flow velocities. As many as 60,000 discharges were …

A Non-Linear Vortex Panel Method For Wings With Edge Separation, Vijay Kalburgi

Mechanical & Aerospace Engineering Theses & Dissertations

A global nodal vortex panel method is developed to predict steady aerodynamic loads on rectangular lifting surfaces with side edge separation. The lifting surface and free shear layers are modeled by bound and free vortex sheets respectively, which are then discretized into triangular bound and free vortex panels respectively. On each triangular panel, a linear distribution of vorticity is defined in terms of the global components of vorticity at its nodes. The velocity field induced by any triangular vortex panel is obtained in closed form. The vortex core of the side edge vortex is modeled by a concentrated core of …

Investigation Of Vscous/Inviscid Interaction In Transonic Flow Over Airfoils With Suction, Chadra S. Vemuru

Mechanical & Aerospace Engineering Theses & Dissertations

The viscous/inviscid interaction over transonic airfoils with and without suction is studied. The streamline angle at the edge of the boundary layer is used to couple the viscous and inviscid flows. The potential flow equations are solved for the inviscid flow field. In the shock region the Euler equations are solved using the method of integral relations. For this the potential flow solution is used as the initial and boundary conditions. An integral method is used to solve the laminar boundary-layer equations. Since both methods are integral methods, a continuous interaction is allowed between the outer inviscid flow region and …

Design Of Multivariable Feedback Control Systems Via Spectral Assignment, Mohsen Marefat

Electrical & Computer Engineering Theses & Dissertations

During the past 15 year s significant advances have been made towards developing viable synthesis- techniques for multivariable feedback control systems. The entire aggregate of this theoretical work has been reviewed and consolidated. Diverse notations have been standardized into a single system. A two-step design philosophy for spectral assignment has been developed which first meets stability and time response requirements by assigning eigenvalues and eigenvector s and then provides for attainment of secondary objectives without significant deviation from the initial assignment. Finally, a computer-aided design package has been created to streamline the process of mathematical calculation and to allow users …

Solar-Assisted Heat Pumps For Low-Temperature Industrial Process Heat Applications, Kamran Fouladi-Semnani

Mechanical & Aerospace Engineering Theses & Dissertations

In recent years, solar energy has been investigated as an alternative to· the fossil fuel based systems for industrial process heat (IPH) applications. Published results in literature indicate that roughly seven percent of total U.S. IPH requirement is in the temperature range of 40-90 °C. The present study, sponsored by Tennessee Valley Authority (TVA), examines the potential of series solar-assisted heat pumps (SAHP) for low-temperature IPH spectrum in the TVA region.

A design method based on utilizability technique is employed to determine the long-term thermal performance of the SAHP system. The transient simulation methodology is also employed to determine the …

Eigenvalue And Eigenvector Design Sensitivity Analysis For Nonlinear Beam Vibrations, Jian-Zhong Yuan

Mechanical & Aerospace Engineering Theses & Dissertations

A beam with immovable ends under large amplitude oscillations is axially subjected to an amplitude-dependent stretching force which is induced by the geometrical nonlinearity. The design sensitivity analysis for such a beam is investigated in this study.

Two variational formulations based on different approximations of nonlinear stretching force are studied firstly. The analytical equations of design sensitivity analysis for these nonlinear eigenproblems are then derived. Finally, a computational scheme using finite element method is developed to calculate the design sensitivity derivatives of the eigenvalue and eigenvector numerically. Numerical examples associated with the nonlinear eigenvalue and eigenvector analysis, as well as …

Analog Computer Simulation With Automatic Scaling By Digital Computer, Mark Anthony Motter

Electrical & Computer Engineering Theses & Dissertations

A computer-aided design approach for the simplification of analog computer simulation is presented. The simulation configuration consists of an EAI 2000 analog computer with serial communications link to a PDP — 11/24 digital computer. Under control of the PDP-11, the analog simulations are realized with appropriate time and magnitude scaling which adjusts the range of the simulation coefficients and prevents overloads of the analog components. The analog computer hardware configuration accommodates both stable plants up to eighth order and closed-loop systems up to tenth order. Cascade compensation is provided for the closed-loop systems.

The plant may be described by either …

Analyses Of Quasi-Isotropic Composite Plates Under Quasi-Static Point Loads Simulating Low-Velocity Impact Phenomena, Ajit Dhundiraj Kelkar

Mechanical & Aerospace Engineering Theses & Dissertations

Composite laminates have high strength to density ratios that make them attractive for use in aircraft structures. However, the damage tolerance of these materials is limited because they have very low ultimate strains, no plastic deformation range, and no usable strength in the thickness direction. These limitations are very obvious when laminates are subjected to impact loads. Due to these impact loads, laminates suffer visible and invisible damage. To improve the material performance in impact requires a better understanding of the deformation and damage mechanics under impact type loads.

In thin composite laminates, the first level of visible damage occurs …

Structural Self-Shadowing And Its Effects On The Thermal-Structural Behavior Of Orbiting Trusses, Jack Mahaney

Mechanical & Aerospace Engineering Theses & Dissertations

The determination of structural shadowing is described. The computation of environmental heat loads for slender structural members in earth orbit is described, and two methods for finite element thermal analysis are described . The effects of self-shadowing on the thermal structural behavior of single truss members and two different trusses are presented. In each case the shadowing produces a noticeable effect on the temperature distributions on truss members, and on the deformations of the trusses.

Analysis And Optimal Design Of Wind Tunnel Balances, Sung-Ling Twu

Mechanical & Aerospace Engineering Theses & Dissertations

The problem of finding the optimal cross-sectional shape of the elastic cage in wind tunnel balance is formulated and solved numerically. A mathematical model to implement the boundary condition associated with the elastic rigid connection into the finite element method is discussed. Numerical results show that the rigid connection at the end of the elastic cage has significant effect on the stress distribution.

The finite dimensional approach for a three dimensional design sensitivity analysis is derived. Using both the free and rigid boundary conditions, numerical examples are performed and comparisons of the accuracy of design sensitivity analysis between the proposed …

Unsteady Transonic Flow Over Slender Bodies, Cevdet Aydun

Mechanical & Aerospace Engineering Theses & Dissertations

The unsteady transonic small disturbance equation for an oscillating slender body is obtained from the full potential equation in cylindrical coordinates by means of a perturbation analysis. The time-dependent body-boundary condition is reduced into a simpler form by matching the outer and inner flows. Also, a time-dependent pressure coefficient over the slender body is derived by means of a matching principle. The simplified form of the body-boundary condition is incorporated into the difference equations at the body axis. This application allows use of the cylindrical coordinate system for the problem. By prescribing several different body-boundary conditions, various modes of body …

Analytic Forms Of Bidirectional Reflectance Functions For Application To Earth Radiation Budget Studies, Natividad Manalo Smith

Mechanical & Aerospace Engineering Theses & Dissertations

Reflected solar radiative fluxes emerging from the Earth's top of the atmosphere are inferred from satellite broadband radiance measurements by applying bidirectional reflectance functions (BDRFs) to account for the anisotropy of the radiation field. BDRFs are dependent upon the viewing geometry (i.e. solar zenith angle, view zenith angle, and relative azimuth angle), the amount and type of cloud cover, the condition of the intervening atmosphere, and the reflectance characteristics of the underlying surface. A set of operational Earth Radiation Budget Experiment (ERBE) BDRFs is available which was developed from the Nimbus 7 ERB (Earth Radiation Budget) scanner data for a …

Computer Aided Simulation Of A Heating, Ventilating, And Air Conditioning System In A Building, Sunil Shrikrishna Kulkarni

Mechanical & Aerospace Engineering Theses & Dissertations

The Godwin Life Science Building on the Old Dominion University campus presents an interesting problem in terms of energy conservation. The building is the maximum energy resource consumer on the campus, having a criterion value of 234 KBtu/sq.ft-year (2657 MJoules/sq. rneter-year). A Simplified Energy Analysis Method (ASEAM) loads and systems computer program was used to simulate the building and its heating, ventilating, and air conditioning (HVAC) plant in order to understand the building's high annual energy resource consumption rate, and to devise ways to overcome it. The main goal was to assess and propose energy conservation improvements to the existing …

Long-Term System Performance Of A Direct Expansion Solar Assisted Heat Pump, Majid Abazeri

Mechanical & Aerospace Engineering Theses & Dissertations

The long-term thermal performance of a direct expansion solar assisted heat pump is determined from the transient system simulation of the system. The system employs a bare collector which also acts as the heat pump evaporator. Of particular interest in this study is the

configuration in which the compressor and the collector area are properly matched from the long-term thermal performance viewpoint. This matching is achieved through continuous as well as two step compressor capacity modulation. In addition to examining the effects of compressor capacity modulation, the effects of various system parameters such as collector area„ storage volume, load temperature, …

Effect Of Wall Temperature Control On Low-Speed Axisymmetric Body Drag, John C. Lin

Mechanical & Aerospace Engineering Theses & Dissertations

This paper presents results of a numerical study of the effect of wall temperature control on the low speed aerodynamic drag of axisymmetric bodies at turbulent Reynolds numbers and zero angle of attack.

Results for both skin-friction and pressure drag were computed for slender bodies using first-order viscous-inviscid interaction theory. Computations using boundary-layer theory were conducted to evaluate the effect of wall heat transfer on bluff-body separation control. Wall heat transfer with 100 percent surface coverage (for all bodies) as well as some partial surface coverage cases were investigated. The wall-to­ tota1-freestream temperature ratio was varied between 0.08 and 2. …