Aerospace Engineering Commons^™

Kinematic Synthesis Of Deployable-Foldable Truss Structures Using Graph Theory, Dirk B. Warnaar

Mechanical & Aerospace Engineering Theses & Dissertations

A graph theoretic approach is applied to the conceptual design of deployable truss structures. The characteristics that relate to the inter-connectivity of the elements of a deployable truss structure can be captured in a schematic representation, called a graph. A procedure is presented that enables the exhaustive generation of these graphs for structures of any given number of nodes and links and which are foldable onto a plane or onto a line.

A special type of truss structures, called truss modules, is presented. Graphs of this class of structures form a subset of the graphs of truss structures. Two procedures …

Prediction And Control Of Asymmetric Vortical Flows Around Slender Bodies Using Navier-Stokes Equations, Tin-Chee Wong

Mechanical & Aerospace Engineering Theses & Dissertations

Steady and unsteady vortex-dominated flows around slender bodies at high angles of attack are solved using the unsteady, compressible Navier-Stokes equations. An implicit upwind, finite-volume scheme is used for the numerical computations.

For supersonic flows past pointed bodies, the locally-conical flow assumption has been used. Asymmetric flows past five-degree semiapex cones using the thin-layer Navier-Stokes equations at different angles of attack, freestream Mach numbers, Reynolds numbers, grid fineness, computational domain size, sources of disturbances and cross-section shapes have been studied. The onset of flow asymmetry occurs when the relative incidence of pointed forebodies exceeds certain critical values. At these critical …

Thermal Compatibility Analysis Of The Passive Damping Treatment Proposed For The Space Shuttle Remote Manipulator System (Srms), Mahesh Chowdhary

Mechanical & Aerospace Engineering Theses & Dissertations

The NASA Space Shuttle Remote Manipulator System (SRMS), due to its long reach and light weight construction has significant structural flexibility. Thus any routine use of SRMS often results in large amplitude oscillations with long settling time. A passive damping technique utilizing a constrained viscoelastic layer damping treatment has been proposed to augment the active control of these oscillations in order to enhance the system stability and the end effector positional accuracy. This thesis concerns with the thermal compatibility analysis of the proposed damping treatment. The necessity for thermal compatibility analysis arises from the fact that acceptable damping performance of …

Effect Of Passive Flow-Control Devices On The Drug Of A Tractor-Trailer Model, Jagjit K. Ahuja

Mechanical & Aerospace Engineering Theses & Dissertations

The aerodynamic drag of tractor trailers is responsible for approximately half of the fuel consumption at highway speeds (55m.p.h.). Thus, it is important that vehicle drag be reduced in order to reduce operating costs and to conserve fuel. The purpose of the subject research conducted in the Old Dominion University Low-Speed Wind Tunnel was to determine the effect of various add-on flow-control devices, such as a cab-mounted flow deflector and gap seals between the tractor and the trailer. In addition, the effect of trailer rear-edge shaping has been studied. This was accomplished by contouring the trailer's rear end. It has …

Dynamics And Control Of Two Suspension Mechanisms For Ground-Based Testing Of Space Structures, Joseph E. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Two suspension systems which effectively simulate a gravity-free environment are presented. A single degree-of-freedom suspension system utilizing a specially profiled band mechanism in conjunction with a torsional spring is presented to show its feasibility and applicability for use as a ground-based testing device for flexible space structures. The second device, a two degree-of-freedom suspension system consisting of two springs and a folding linkage is presented to show the feasibility as a testing device for suspending space structures on earth.

Problems resulting in unwanted dynamic behavior due to deviations from the design parameters for both systems are addressed. A nonlinear controller …

Integrated Control Of Thermally Distorted Large Space Antennas, Robert H. Tolson

Mechanical & Aerospace Engineering Theses & Dissertations

Studies on controlling the thermal distortion of large space antennae have generally investigated a single orbital position and have optimized actuator locations based on minimizing the RMS surface deviation from the original parabolic shape. One study showed the benefits of directly using far zone electric field characteristics as the performance measure; but, this approach resulted in a nonlinear programming problem. The objective of the current study is to develop an approach to designing a control system that (1) recognizes the time dependence of the distortion and (2) controls variables that are directly related to far field performance in a quadratic …

Development Of A Perturbation Generator For Vortex Stability Studies, John Edward Riester Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Theory predicts vortex instability when subjected to certain types of disturbances. It was desired to build a device which could introduce controlled velocity perturbations into a trailing line vortex in order to study the effects on stability. A perturbation generator has been designed and manufactured which can be attached to the center-body of an airfoil type vortex generator. Details of design tests and manufacturing of the perturbation generator are presented. The device produced controlled perturbations with frequencies in excess of 250 Hz. Preliminary testing and evaluation of the perturbation generator performance was conducted in a 4 inch cylindrical pipe. Observations …

Navier-Stokes Simulations Of Flows About Complex Configurations Using Domain Decomposition Techniques, Kamran Fouladi-Semnani

Mechanical & Aerospace Engineering Theses & Dissertations

An algorithm is developed to obtain numerical simulations of flows about complex configurations composed of multiple and nonsimilar components with arbitrary geometries. The algorithm uses a hybridization of the domain decomposition techniques for grid generation and to reduce the computer memory requirement. Three dimensional, Reynolds-averaged, unsteady, compressible, and complete Navier-Stokes equations are solved on each of the subdomains by a fully-vectorized, finite-volume, upwind-biased, approximately-factored, and multigrid method. The effect of Reynolds stresses is incorporated through an algebraic turbulence model with several modifications for interference flows. The present algorithm combines the advantages of an efficient, geometrically conservative, minimally and automatically dissipative …

Grid Generation And Flow Computation About A Martian Entry Vehicle, John Edward Stewart

Mechanical & Aerospace Engineering Theses & Dissertations

A number of vehicles are currently being proposed for a manned mission to Mars. One of these vehicles has a modified blunt-nosed cone configuration. Experimental results have been obtained for this vehicle in 1968. These results show lift-over-drag ratios comparable to those needed for Mars entry. Computations are performed here to verify the earlier results and to further describe the flight characteristics of this vehicle.

An analytical method is used to define the surface of this vehicle. A single-block volume grid is generated around the vehicle using an algebraic Two-Boundary Grid Generation algorithm (TBGG) and transfinite interpolation. Euler solutions are …

The Influence Of Payload Dynamics On Trajectory Tracking Performance Of Robot Manipulator, Atul G. Kelkar

Mechanical & Aerospace Engineering Theses & Dissertations

Future space mission plans call for extensive use of remote manipulator systems for tasks such as assembly of lunar vehicles or space station modules, servicing of satellites, etc. These tasks demand very high precision end-effector motion control. Methods for compensating manipulator dynamics to achieve better trajectory tracking performance have been investigated by many researchers. Still, it is not always clear whether the added complexity of dynamic compensation is warranted for a given system. As an aid in evaluating when dynamic compensation is required, this thesis presents a method for the determination of maximum endpoint tracking error due to uncompensated inertial …

An Experimental Study Of An Axisymmetric Turbulent Boundary Layer Disturbed By A Periodic Freestream, Chithrabhanu Koodalattupuram

Mechanical & Aerospace Engineering Theses & Dissertations

Behavior of an axisymmetric equilibrium turbulent boundary layer disturbed by a propeller wake in the freestream was investigated experimentally. Tests were conducted in a low speed wind tunnel and measurements of turbulence quantities were made using an X wire probe and a constant temperature anemometer. The boundary layer flow on a cylindrical body was characterized by measuring its gross parameters and comparing them with classical values. Propeller speed was measured using an electronic circuit whose output signal was also used to trigger hot wire probe. Gross boundary later characteristics of the disturbed boundary layer did not deviate appreciably from the …

Control And Mechanism Interaction For Ground-Based Testing Of Space Structures, Li-Farn Yang

Mechanical & Aerospace Engineering Theses & Dissertations

In the ground-based validation testing, the adverse effect of terrestrial conditions such as a gravitational force interferes with the dynamic behavior of space structures. A suspension system is developed to assess the structural characteristics in a simulated zero-gravity environment. Using a mechanisms approach, the synthesis of a noncircular disk with a torsional spring at its rotational axis is designed to counteract the gravitational force of test structures during the testing.

The multibody dynamics of a flexible steel beam carried on a rigid trolley has been investigated. The system is constructed in such a way that the rapid and large-angle slewing …

Eigensensitivity Analysis For Space Structures With Applications In Design Optimization, Sean Patrick Kenny

Mechanical & Aerospace Engineering Theses & Dissertations

Eigensensitivity analysis is concerned with the rates of changes of eigenvalues and eigenvectors with respect to design variables. Eigensolutions of space structures are found to display four distinct characteristics, three of which are related to various types of repeated eigenvalues. This study will address three cases of the real symmetric structural eigenvalue problem. The three cases that will be considered are: distinct eigenvalues, repeated eigenvalues with distinct first eigenvalue derivatives, and repeated eigenvalues with infinitely repeating eigenvalue derivatives. Analytic formulations for eigenvalue/ vector derivatives will be presented for each of the three cases. The directional differentiability of eigenvalues for the …

Navier-Stokes Analysis Of Cold Gas Scramjet Nozzle-Afterbody Flowfields, Walter C. Engelund

Mechanical & Aerospace Engineering Theses & Dissertations

The recent renewal of interest in hypersonic aerodynamics, brought about largely in part due to the development of the National Aerospace Plane (NASP), is resulting in an increased reliance on computational fluid dynamics for flowfield data in this flight regime. The design of the nozzle-afterbody section for a hypersonic transport such as the NASP is currently underway, and is being conducted using both computational fluid dynamics and cold, non-reacting, simulant gas experimental models. In this study, a computational analysis is conducted for the flow through a scramjet nozzle-afterbody test section.

Computations have been performed for a cold gas simulation of …

Domain Decomposition For Multigrid, Finite Volume Flow Solvers, Victor Robert Lessard

Mechanical & Aerospace Engineering Theses & Dissertations

Computing the flow fields about three-dimensional complex configurations accurately becomes a difficult task, if it is attempted to generate a single, body fitted grid with proper clustering. The domain decomposition methods, which divide the computational domain into less complex subdomains, are extensively used to decrease the grid generation workload. A domain decomposition technique also allows the use of different solution methods for different subdomains. The objective of this work is to develop a domain decomposition method via overlapping/embedding the component grids, which is to be used by upwind, multigrid, finite volume solution algorithms. A computer code, given the name MaGGiE, …

Evaluation Of Equilibrium Turbulence For A Hypersonic Boundary Layer At Nonadiabatic Wall Conditions, Cindy W. Albertson

Mechanical & Aerospace Engineering Theses & Dissertations

This paper presents an experimental study to characterize the compressible turbulent boundary layer produced along a flat plate in the NASA Langley 8-Foot High Temperature Tunnel and determine the test conditions necessary to achieve equilibrium turbulence. In addition, the present study extends the data base for equilibrium compressible turbulent boundary layers over quasi-isothermal walls which are far from the adiabatic wall temperature. The measurements consist of pilot pressure, static pressure, and total temperature distributions in the boundary layer. A flat plate measuring 9.7 feet long and 4.3, feet wide was used for the study to provide a naturally turbulent boundary …

Low Speed Flowfield Characterization By Infrared Measurements Of Surface Temperatures, Ehud Gartenberg

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental program was aimed at identifying areas in low speed aerodynamic research where infrared imaging systems can make significant contributions. Implementing a new technique, a long electrically heated wire was placed across a laminar jet. By measuring the temperature distribution along the wire with the IR imaging camera, the flow behavior was identified. Furthermore, using Nusselt number correlations, the velocity distribution could be deduced. The same approach was used to survey wakes behind cylinders in a wind-tunnel. This method is suited to investigate flows with position dependent velocities, e.g., boundary layers, confined flows, jets, wakes and shear layers. It …

An Adaptive Remeshing Finite Element Method For High-Speed Compressible Flows Using Quadrilateral And Triangular Elements, Gururaja R. Vemaganti

Mechanical & Aerospace Engineering Theses & Dissertations

In this study a new adaptive remeshing method for high speed compressible flow analysis is presented. The method uses quadrilateral elements where possible, and triangles are introduced as needed. The primary goal of this study is to develop a remeshing method which uses both the concepts of unstructured and structured meshes for the finite element analysis to predict accurate aerodynamic heating in problems related to high speed viscous flows. The remeshing method uses a solution based on an old mesh to create a new mesh based on an advancing front technique. In the present implementation, a structured mesh of quadrilaterals …

Expert Systems For Automated Maintenance Of A Mars Oxygen Production System, Ming-Tsang Ho

Mechanical & Aerospace Engineering Theses & Dissertations

A prototype expert system has been developed for maintaining autonomous operation of a Mars oxygen production system. Normal operation conditions and failure modes according to certain desired criteria are tested and identified. Several schemes for failure detection and isolation using forward chaining, backward chaining, knowledge-based and rule-based are devised to perform several housekeeping functions. These functions include self-health checkout, an emergency shut down program, fault detection and conventional control activities. An effort has been made to derive the dynamic model of the system using Bond-Graph technique in order to develop the model-based failure detection and isolation scheme by estimation method. …

Effects Of Nose Bluntness And Shock-Shock Interactions On Blunt Bodies In Viscous Hypersonic Flows, Dal J. Singh

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study has been conducted to investigate the effects of blunt leading edges on the viscous flow field around a hypersonic vehicle such as the proposed National Aero-Space Plane. Attention is focused on two specific regions of the flow field. Analysis of these flow regions is required to accurately predict the overall flow field as well as to get necessary information on localized zones of high pressure and intense heating.

The forebody is modeled by slender cones and ogives with spherically blunted nose. A combination of Navier-Stokes and parabolized Navier-Stokes equations is used to compute the flow field. The …

A Finite Element Formulation For The Large Deflection Random Response Of Thermally Buckled Structures, James Eugene Locke

Mechanical & Aerospace Engineering Theses & Dissertations

The effects of temperature and acoustic loading are included in a theoretical finite element large deflection formulation for thin, isotropic plate and beam type structures. Thermal loads are applied as steady-state temperature distributions, and acoustic loads are taken to be stationary and Gaussian with zero mean and uniform magnitude and phase over the surface of the structure. Material properties are considered to be independent of temperature. Also, inplane and rotary inertia terms are assumed to be neglegible, and all inplane edge conditions are taken to be immovable. For the random vibration analysis, cross correlation terms are included.

The nature of …

Numerical Simulation Of Turbulent Flows Past Three-Dimensional Cavities, Shivakumar Srinivasan

Mechanical & Aerospace Engineering Theses & Dissertations

Computations have been performed to simulate turbulent supersonic, transonic, and subsonic flows past three-dimensional deep, transitional, and shallow cavities. Simulation of these self sustained oscillatory flows has been generated through time accurate solutions of Reynolds averaged full Navier-Stokes equations using the explicit MacCormack scheme. The Reynolds stresses have been modeled, using the Baldwin-Lomax algebraic turbulence model with certain modifications. The computational results include instantaneous and time averaged flow properties everywhere in the computational domain. Time series analyses have been performed for the instantaneous pressure values on the cavity floor. Comparison with experimental data is made in terms of the mean …

Calculations Of Three-Dimensional Transonic Flows Using The Implicit Formulation Of The Isenthalpic Euler Equations With Flux Vector Splitting, Frank E. Cannizzaro

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical method for solving three-dimensional transonic flows using the isenthalpic formulation of the Euler equations is developed. The method uses van Leer's flux vector splitting to solve the implicit formulation of the governing equations, which are applied to a cell centered finite-volume scheme. A three factor spatial approximate factorization is implemented in solving the implicit part of the governing equations. Time marching to a steady state solution requires short computational times due to the relative efficiency of the basic method. Computational times are further reduced by the implementation of the multigrid acceleration technique, which provided converged solutions in approximately …

Full-Potential Integral Solutions For Steady And Unsteady Transonic Airfoils With And Without Embedded Euler Domains, Hong Hu

Mechanical & Aerospace Engineering Theses & Dissertations

The integral equation solution of the full-potential equation is presented for steady and unsteady transonic airfoil flow problems. The method is also coupled with an embedded Euler domain solution to treat flows with strong shocks for steady flows.

For steady transonic flows, three integral equation schemes are well developed. The first two schemes are based on the integral equation solution of the full-potential equation in terms of the velocity field. The Integral Equation with Shock-Capturing (IE-SC) and the Integral Equation with Shock-Capturing Shock-Fitting (IE-SCSF) schemes have been developed. The IE-SCSF scheme is an extension of the IE-SC scheme, which consists …

Direct Simulation Of Hypersonic Transitional Flows Over Blunt Slender Bodies, Vincent Cuda Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Hypersonic transitional flow has been studied using the Direct Simulation Monte Carlo method. The cylindrically blunted wedge and spherically blunted cone were examined for body half angles of 0°, 5° and 10°, at a flight velocity of 7.5 km/s, zero angle of incidence and altitudes of 70 to 100 km. Those geometries and flow conditions are important considerations for hypersonic vehicles currently under design. Surface chemistry was examined for diffuse, finite-catalytic surfaces. Nonequilibrium chemistry and nonequilibrium thermodynamics were considered for both configurations at all altitudes.

Numerical simulations showed that rarefied gas effects, such as surface temperature jump and velocity slip, …

An Evaluation Of A Taylor-Galerkin Algorithm For High Speed Inviscid Flows Using Quadrilateral And Triangular Elements, Kim S. Bey

Mechanical & Aerospace Engineering Theses & Dissertations

The Taylor-Galerkin finite element algorithm is used to obtain solutions to the two-dimensional compressible Euler equations. The mathematical formulation of the algorithm is presented for a typical scalar equation. The derivation results in element equations which are assembled over the entire solution domain to obtain the system of equations that are solved explicitly. The algorithm has the unique feature that the finite element matrices can be evaluated in closed form, avoiding expensive numerical integration. Aspects of vector programming strategies and mesh generation important to an effective analysis procedure are also described. Solutions to supersonic flow problems with exact solutions are …

Dynamic Analysis Of An Earth-Orbiting Satellite Deploying Hinged Appendages, Kevin Fielding Oakes

Mechanical & Aerospace Engineering Theses & Dissertations

The planar liberational dynamics of an arbitrary spacecraft with deployable hinged appendages is presented here both analytically and numerically. The system model consists of a central rigid satellite moving about the earth in a circular orbit at a uniform orbital rate. Attached to the satellite are two unfolding rigid booms with specified mass and length. Tip masses are included at the ends of each boom and deployment is driven by torsional springs at both frictionless hinge points. The equations of motion are developed for both a single- and double-appendage model through the use of Lagrange's equations. The formulation accounts for …

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 …

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 …