Mechanical Engineering Commons^™

Finite Element Analysis Of Thermal Post-Buckling And Vibrations Of Thermally Buckled Composite Plates, Charles Clifton Gray

Mechanical & Aerospace Engineering Theses & Dissertations

The development of supersonic and hypersonic flight vehicles such as the High Speed Civil Transport and the National Aero-Space Plane has created an increased need for analysis of structures at very high temperatures. Bisplinghoff and Pian, Yang and Han, and Dokmeci and Boley have conducted experimental and analytical studies to determine the effect of elevated temperatures on the vibration characteristics of isotropic plates, Chen and Chen, and Meyers and Hyer have clone studies on thermal buckling and post-buckling of composite plates, respectively.

The thermal loads which will be imposed on the new high speed aircraft will be too great for …

Simulation Of 3-D Viscous Flow Around A Nozzle-Afterbody At High Speeds, Wendy B. Hoffman

Mechanical & Aerospace Engineering Theses & Dissertations

Turbulent shear flows at supersonic and hypersonic speeds around a nozzle-afterbody are numerically simulated and investigated. The specific application is for the flow around the nozzle-afterbody of a generic hypersonic vehicle. Accurate simulation of viscous, separating flows is not an easy task, and it is complicated by turbulence modeling concerns. A main objective of this study is to numerically simulate the afterbody flowfield while addressing the turbulence modeling problem. The viscous flow considered i~ this study is characterized by three-dimensional corner flows, shock boundary layer interactions, plume flow, shear layers, and cross-flow separations. Accurate simulation of this flow requires solution …

Investigation Of Effects Of Nose Bluntness And Angle Of Attack On Slender Bodies In Viscous Hypersonic Flows, Ashwini Kumar Sehgal

Mechanical & Aerospace Engineering Theses & Dissertations

Hypersonic flows over cones and straight biconic configurations are calculated for a wide range of free stream conditions in which the gas behind the shock is treated as perfect. Effect of angle of attack and nose bluntness on these slender bodies in air is investigated extensively. The numerical procedures are based on the solution of complete Navier-Stokes equations at the nose section and parabolized Navier Stokes equations further downstream. The flow field variables and surface quantities show significant differences when the angle of attack and nose bluntness are varied. The complete flow field is thoroughly analyzed with respect to velocity, …

Large-Amplitude Finite Element Flutter Analysis Of Composite Panels In Hypersonic Flow, Carl E. Gray Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

A finite-element approach is presented for determining the nonlinear flutter characteristics of two-dimensional isotropic and three-dimensional composite laminated thin panels using the third-order-piston, transverse loading, aerodynamic theory. The unsteady, hypersonic, aerodynamic theory and the von Karman large deflection plate theory are used to formulate the aeroelastic problem. Nonlinear flutter analyses are performed to assess the influence of the higher-order aerodynamic theory on the structure's limit-cycle amplitude and the dynamic pressure of the flow velocity. A solution procedure is presented to solve the nonlinear panel flutter and large-amplitude free vibration finite element equations. This procedure is a linearized updated mode with …

Maximum Likelihood Estimation For Distributed Parameter Models Of Large Beam-Like Structures, Ji Yao Shen

Mechanical & Aerospace Engineering Theses & Dissertations

Proposed large space structures have many characteristics that give an advantage to modeling their structural dynamics by a set of partial differential equations (PDE's). By far, the most effort put forth in studying system identification and control to date has been based on finite element models. Despite its acceptability, such lumped parameter models have inevitable deficiencies primarily because of their complexity. Both approaches are complementary and each should be used where it is most effective. But the fact is that the distributed parameter approach has not been developed to the level of maturity as for the lumped parameter approach.

Motivated …

Two-Dimensional Heat Loss From A Building Slab Including Convective Effects In Saturated Soil, William W. Rust Iii

Mechanical & Aerospace Engineering Theses & Dissertations

The heat loss from a building slab was investigated. The continuity equation, Darcy's Law and the energy equation were formulated to include the temperature dependence of viscosity and density of water. The governing equations and appropriate boundary conditions were transformed into dimensionless variables. A finite difference numerical scheme was constructed based on the Gauss-Seidel method by lines and solved iteratively in alternating directions. A correlation between the geometrical characteristics of the domain, the convective surface heating parameters, and the total nondimensional slab heat loss in two dimensions was discovered. Furthermore, the correlation was extended to three-dimensional slabs and produced good …

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 …

Numerical Modeling Of Flame Lift-Off Phenomenon And Calculation Of Thermal Loads On A Methane Fuel Injector With Complex Geometry, Taj O. Mohieldin

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical study has been conducted to analyze a fuel injector with three in-line cylinder geometry that has been adopted as a model for investigating the combustion phenomenon in the 8-Foot High Temperature Tunnel (HTT) combustor at the NASA Langley Research Center. The primary objective here is to analyze the flame lift-off phenomenon in the three cylinder fuel injector geometry in two-dimensions. The fluid mechanics model used in the analysis includes time-averaged Navier-Stokes equations that are employed in conjunction with a two-equation k-$\epsilon$ model for predicting the effects of turbulence. Calculations were performed with three chemistry models, namely fast chemistry, …

The Effectiveness Of Viscoelastic Damping Treatments On A Flexible Manipulator Subjected To Torsional Loads, Leah L. Remias

Mechanical & Aerospace Engineering Theses & Dissertations

The advent of new technology has led to an increasing number of missions in space. The space shuttle Remote Manipulator System (RMS) is a lightweight flexible manipulator currently used in NASA space missions. The future role of the RMS and similar flexible manipulators may include in-space construction and assembly tasks. Because these tasks require precise motion and short settling time of the end-point oscillations, effective vibration control schemes are being investigated.

Passive damping techniques have shown to provide a considerable amount of damping in controlling flexural vibrations. In this research passive damping via constrained viscoelastic damping treatments is explored as …

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 …

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 …

Finite Element Analysis Of Structures With Constrained Viscoelastic Layer Damping, Yung Chen

Mechanical & Aerospace Engineering Theses & Dissertations

It has been demonstrated that constrained viscoelastic layer damping treatments provide an effective means of passive control for structural vibration. These treatments dissipate vibrational energy by inducing shear strain in a thin layer of viscoelastic material. Our interest is in adding passive damping to a structure as an augmentation to active control. For such applications it is desirable to achieve high damping performance in a given frequency range with a minimum of added weight. Most damping treatments employ spatially continuous constraining layers over the entire viscoelastic layer. Plunkett and Lee have shown that the effectiveness of the damping treatment can …

Investigation Of Mixing Characteristics Of A Lox Injector Operating At Non-Ideal Thermodynamic Conditions, W. Wei

Mechanical & Aerospace Engineering Theses & Dissertations

The mixing characteristic of a liquid oxygen (LOX) injector operating under nonideal thermodynamics conditions are analyzed. Oxygen, in supercritical state, is injected into a high pressure airstream flowing through a narrow annulus region of a hypersonic wind tunnel. The objective of the present study is to investigate conditions that would help produce a uniform profile of oxygen concentration at the end of a diverging mixing channel, located downstream of the injector section. Uniformity of oxygen concentration profile is critical to combustion processes that occur downstream of the LOX injector section.

The coupled velocity, temperature, oxygen concentration and enthalpy fields are …

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 …

Use Of A Generalized Set Of Variables In Fluid Flow Calculations, Pawel Chwalowski

Mechanical & Aerospace Engineering Theses & Dissertations

In fluid flow calculations, a set of generalized field variables is used to replace the more conventional choice of either the conserved variables, or the primitive variables. This generalized set of variables represents an infinite number of possible choices for the specific set of field variables. For algorithms of both the implicit and explicit type, the resulting effect of a change in field variables on a steady-state flow solution is in general relatively small. However, for implicit algorithms, a consistent linearization with respect to the new variables results in dramatic changes in the overall matrix conditioning of the linear systems …

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 …

A Systematic Procedure For The Analysis And Design Of Deployable Space Structures, Praveen Kumar

Mechanical & Aerospace Engineering Theses & Dissertations

An integrated graph theory and a symmetry-based approach have been developed for the type synthesis of deployable truss structures. Using this systematic approach, a bay of a deployable structure may be looked upon as being built around an axis or a plane of symmetry, including anti-symmetry. By providing a fictitious joint along this axis, the problem of structural design and analysis can be reduced to the study of one plane or face of the given structure. Each face is considered to be an assemblage of structural links connected by joints which form a closed kinematic chain. The conventional graph representation …

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 …

Radiative Interactions In Laminar Duct Flows, Prakash A. Trivedi

Mechanical & Aerospace Engineering Theses & Dissertations

Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a Parallel Plate Duct and a Circular Duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO₂, and H₂O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's …

Synthesis Of An Efficient Band Mechanism For Robots And Prosthetic Devices, Run Chen Zhou

Mechanical & Aerospace Engineering Theses & Dissertations

A noncircular pulley has been applied to improve the system efficiency of an electrical-powered elbow prosthesis. The dynamics of the motor and the prosthetic arm have been incorporated into the kinematic synthesis relationships for determining the pulley profile that maximizes the efficiency of the elbow prosthesis.

The nonlinear dynamic equations have been solved by the code Differential Equation (DE) while determining the motor power and efficiency which are the criteria in the nonlinear programming problem. The optimal design variables for determining the pulley profile along with some simulation results have been obtained from an optimization program (based on the Generalized …

Non-Linear Dynamics And Control For Thermal Room Models, Milind Prabhakar Oak

Mechanical & Aerospace Engineering Theses & Dissertations

Heating, Ventilation and Air Conditioning (HVAC) building operations with emphasis on reduced energy costs and occupant comfort require a dynamic control of short response (minutes) elements of HVAC systems. Hence, it is imperative to acquire better methods of non-linear modeling for prescription of thermal controls which will regulate space conditions over wide parameter ranges without undue cycling or steady state errors. A first step towards this goal is identification and inclusion of short response dynamics elements in the HVAC systems model while retaining essential non-linearities. A single zone environmental chamber is modeled in the heating mode. In the model, …

Comparison Of Digital Controllers Used In Magnetic Suspension And Balance Systems, William Allen Kilgore

Mechanical & Aerospace Engineering Theses & Dissertations

Dynamic systems that were once controlled by analog circuits are now controlled by digital computers. Presented is a comparison of the digital controllers presently used with magnetic suspension and balance systems. The overall response of the systems are compared using a computer simulation of the magnetic suspension and balance system and the digital controllers. The comparisons include responses to both simulated force and position inputs. A preferred digital controller is determined from the simulated responses.

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, …

The Effects Of Bending On The Strain Distributions In A Stiffener-Skin Interface Region, Osvaldo F. Lopez

Mechanical & Aerospace Engineering Theses & Dissertations

An analytical and experimental study to assess the effect of bending on the adhesive strain distributions in a stiffener-skin interface region is described. A one-dimensional beam analysis is derived using a variational approach. Parametric studies are conducted to assess the effects of stiffener, skin, and adhesive thickness and adhesive material nonlinearity on the adhesive layer extensional and shear strain distributions subjected to applied bending. Two experimental methods of measuring through-the-thickness extensional strains in an adhesive are investigated. One method involves measuring the changes in the resistance of a composite strain sensor subjected to applied tension and compression loads. The second …

Application Of Shape Sensitivity Analysis For Computation Of Transient Free-Surface Flows, Frank Nicolas Michel

Mechanical & Aerospace Engineering Theses & Dissertations

Shape sensitivity analysis is introduced into a numerical scheme simulating a transient free-surface flow and applied to the case of a fluid advancing through a bed of cylinders. For this incompressible Newtonian flow, viscous forces are dominant. A penalty function finite element formulation is used to solve the problem. Coordinates of nodes on the moving boundary are chosen as design variables and an analytical formulation of the gradient of the finite element algebraic system, with respect to these variables, is derived.

In a numerical example, the results obtained with and without sensitivity analysis are compared. The efficiency and accuracy of …

Investigating The Method Of Structural Topological Variations For Sensitivity Analysis And Design Optimization, Niki A. Mehta

Mechanical & Aerospace Engineering Theses & Dissertations

The method of structural topological variations is a newly developed technique for analysis of frame structures. It provides a novel method that completely avoids formulating and solving simultaneous equations, required in the finite element displacement method. The principal objective of this thesis is to investigate the method of topological variations as a possible design tool and study its applicability in the sensitivity analysis and in the process of design optimization.

A computer code was developed for this method to obtain its comparative performance against the finite element displacement method. For analysis of large structures involving frequent local modifications, the method …