Engineering Science and Materials Commons^™

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

Mechanical & Aerospace Engineering Faculty Publications

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 responses 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.

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 …

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 …

Finite Element Formulation And Numerical Simulation Of The Large Deflection Random Vibration Of Laminated Composite Plates, Jay Howard Robinson

Mechanical & Aerospace Engineering Theses & Dissertations

A theoretical large deflection finite element formulation is developed for the purpose of simulating the random vibration of thin generally laminated composite plates. The random acoustic load is taken to be stationary and Gaussian with zero mean and uniform magnitude and phase over the surface of the plate. In­ plane inertia terms are included in the formulation however rotary inertia terms are assumed negligible.

The integration routine is derived from a set of unified single step algorithms, using a weighted satisfaction of the equilibrium equation. The algorithm is second order accurate and unconditionally stable for particular values of its free …

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 …

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 …

A Detailed Analysis Of Dynamic Robotic Simulation, Lonnie J. Love

Mechanical & Aerospace Engineering Theses & Dissertations

Future space missions may require the utilization of automation technology for assembly, maintenance, repair, and a variety of repetitive or hazardous operations. Many tasks which are likely candidates for robotic or telerobotic execution are either difficult or impossible to duplicate in the laboratory. With an accurate simulation package, many of these tasks can be evaluated by computer simulation before committing the resources required for laboratory experimentation. With this motivation, the ROBSIM robot simulation software has been developed by NASA Langley Research Center in conjunction with the Martin Marietta Corporation. ROBSIM is a versatile tool with features including the ability to …

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 …

Hydrogenation Effects On Trap Related Conduction In Diamond, Linwood Cleveland Watkins Iii

Electrical & Computer Engineering Theses & Dissertations

In this research work, the results of an experimental investigation on the electrical conduction mechanism in type Ιa and Ilb diamonds are presented. These results are compared with those of previous theoretical studies. The basic physical properties of diamond are discussed. Details of ohmic contact formation on diamond are presented.

The current-voltage characteristics revealed the presence of traps located below the Fermi level. The unfilled trap density was determined. The deep traps were further studied using spectroscopic photoconductivity measurements and the trap energy levels were determined.

The effects of hydrogenation on trap related conduction were studied subsequently. Hydrogenation was carried …

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 …

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.

Stability Design Of A Slender Column With Curved Longitudinal Stiffeners, Mark S. Lake

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis presents the results of a stability design study of a slender column with curved longitudinal stiffeners for large space structure applications. The stiffened column concept is attractive because it allows the buckling load of a slender column to be increased at a fairly low cost in increased mass, and at no change in the column packaged size. Linear stability analyses are performed using a "linked-plate" representation of the stiffeners to determine stiffener local buckling stresses. Results from a set of parametric analyses are used to determine an approximate explicit expression for stiffener local buckling in terms of its …

Global/Local Stress Analysis Of Composite Structures, Jonathan B. Ransom

Mechanical & Aerospace Engineering Theses & Dissertations

A method for performing a global/local stress analysis is described and its capabilities are demonstrated. The method employs spline interpolation functions which satisfy the linear plate bending equation to determine displacements and rotations from a global model which are used as "boundary conditions" for the local model. Then, the local model is analyzed independent of the global model of the structure. This approach can be used to determine local, detailed stress states for specific structural regions using independent, refined local models which exploit information from less-refined global models. The method presented is not restricted to having a priori knowledge of …

Explicit And Implicit Calculations Of Turbulent Cavity Flows With And Without Yaw Angle, Guan-Wei Yen

Mechanical & Aerospace Engineering Theses & Dissertations

Computations have been performed to simulate turbulent supersonic flows past three-dimensional deep cavities with and without yaw. Simulation of these self-sustained oscillatory flows have been generated through time accurate solutions of the Reynolds averaged complete Navier-Stokes equations using two different schemes: (1) MacCormack, finite-difference, (2) implicit, upwind, finite-volume schemes. The second scheme, which is approximately 30% faster, is found to produce better time accurate results. 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 …

Determinations Of Molecular Weight And Molecular Weight Distribution Of High Polymers By The Rheological Properties, Joan Y. Z. Huang

Mechanical & Aerospace Engineering Theses & Dissertations

Several methods are reviewed by which the molecular weight (MW) and molecular weight distribution (MWD) of polymeric material were determined from the rheological properties. A poly (arylene ether) polymer with six different molecular weights was used in this investigation. Experimentally measured MW and MWD were conducted by GPC/LALLS (Gel Permeation Chromatography/Low Angle Laser Light Scattering), and the rheological properties of the melts were measured by a Rheometric System Four rheometer. It was found that qualitative information of the MW and MWD of these polymers could be derived from the viscoelastic properties, with the methods proposed by Zeichner and Pate1, and …

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 …

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. …

The Effects Of Nonlinearities On The Optimal Design Of Forced Vibrating Beams, Cheryl Celestine Jackson

Mechanical & Aerospace Engineering Theses & Dissertations

The optimal design of a beam under harmonic excitations is formulated and solved numerically for linear and nonlinear forced vibration theories. The beam has a nonuniform cross-sect ion, whose thickness can change during the optimization procedure. Based on the numerical results, for the given input frequency range, the linear vibration theory produces a more conservative design than the nonlinear vibration theory.

The analytical formulation for both theories is presented. For the linear case, a mean case is defined for the self-weight on a beam, and an alternating case is defined for input forcing frequencies which cause fatigue variations on a …

Large Planar Maneuvers For Articulated Flexible Manipulators, Li-Farn Yang

Mechanical & Aerospace Engineering Theses & Dissertations

An articulated flexible manipulator carried on a translational cart is maneuvered by an active controller to perform certain position control tasks. The nonlinear dynamics of the articulated flexible manipulator are derived and a transformation matrix is formulated to localize the nonlinearities within the inertia matrix. Then a feedback linearization scheme is introduced to linearize the dynamic equations for controller design. Through a pole placement technique, a robust controller design is obtained by properly assigning a set of closed loop desired eigenvalues to meet performance requirements. Numerical simulations for the articulated flexible manipulators are given to demonstrate the feasibility and effectiveness …

The Effect Of Elastic Boundary Conditions On The Dynamic Response Of Rectangular Plates, Terry K. Brewer

Mechanical & Aerospace Engineering Theses & Dissertations

Natural frequencies and forced steady-state harmonic response for the vibration of uniform rectangular plates with edges elastically restrained against rotation and transverse translation are addressed. A single mode Rayleigh-Ritz solution is derived using functions that describe the normal modes of vibration of a beam whose ends are elastically restrained. The finite element solution is obtained for comparison. MACSYMA symbolic manipulation system is implemented as an aid to the mathematical rigor of the Ritz approach and NASTRAN finite element code is used to model the mechanical system. Comparisons are made to published results and the solutions of this study are found …

An Application Of Global Optimization Algorithm For Modal Parameter Identification, Chung-Men Chen

Mechanical & Aerospace Engineering Theses & Dissertations

Single-mode projection filters for modal parameter identification for flexible structures are introduced. An effective two-dimensional global optimization method using interval analysis is combined with the projection filters to facilitate identification for modal frequency and damping. A numerical simulation of a ten-mode structure is presented to illustrate the feasibility of the new method. The projection filters are practical for parallel processing implementation.

Development Of Load Carrying Thermoplastic Components For An Automotive Emergency Braking System, Joseph Gerard Sikora

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis describes a classical approach to plastic parts' design leading to the development of load carrying fiber reinforced thermoplastic components for use in an automotive emergency braking system. The control arms that are the focus of this study are designed to withstand the static loads characteristic of the loads experienced by an automotive emergency braking system. The present study is particularly significant as a case study because the design involves development of load carrying components for use in the harsh automotive environment.

Beginning with a fundamental concept for the control arms, basic design criteria, and a limited insight into …

Analysis And Design Sensitivity Computations Of Nonlinear Free And Forced Vibrations Of Stepped Beams, Yong Xiang Xue

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element method is developed in this thesis for analyzing stepped beams under nonlinear free and forced vibrations. A new assumption is made to improve an existing finite element procedure for treating beams of nonuniform cross sections. The geometric nonlinearity results from the nonlinear, strain-displacement relation due to large deflection of a beam.

Based on an improved finite element procedure a computational method is then established for design sensitivity analyses of nonlinear eigenproblems pertaining to the free and forced nonlinear vibrations of beams. It is found that the equation for computing the design sensitivity of eigenvector is linear and …

Analysis And Optimal Design Of Pyramidal Truss Core Panels, Mark A. Wiseman

Mechanical & Aerospace Engineering Theses & Dissertations

The Pyramidal Truss Core Panel has been developed to save weight in applications normally devoted to solid plates. Present design formulas use classical beam theory with engineering assumptions made for moment of inertia and shear modulus determinations. Analysis with the SUPERSAP finite element code indicates that the present theory provides good prediction for the plate stresses but may be inadequate for the core stress and deflection determination. Two optimization routines are presented. The first procedure uses a batch file to execute separate programs with SUPERSAP used as the analysis code. The second combines a FORTRAN program used for analysis with …

Experimental Parametric Study Of A True Airspeed Sensor, Adel R. Ibrahim

Mechanical & Aerospace Engineering Theses & Dissertations

The results of an experimental parametric study of a true airspeed sensor are presented. The objective of this study was primarily to investigate experimentally the parameters that effect the frequency response of the true airspeed sensor. A secondary objective was to identify the sensor configuration which achieved the best performance. The model used to conduct these experiments basically consisted of swirl generator and vortex tube sections and pick-up signal system. A regression analysis was performed on the experimental results to obtain the effect of each parameter individually on the frequency response. The most significant parameters were selected by the regression …

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 …

Optimal Cure Cycle Design Of A Resin-Fiber Composite Laminate, Jeenson Sheen

Mechanical & Aerospace Engineering Theses & Dissertations

High performance polymeric composites have been experiencing increasing usage in the aerospace and automobile industries. Such materials are commonly composed of long or chopped fibers embedded in the thermosetting resin matrix. Changes in physical and chemical properties of such composite materials during the cure process are rather complex. Thus, it is not a trivial task to properly design a cure cycle (temperature and pressure profiles) for a cure process. The material should be cured uniformly and completely with the lowest void content; the temperature inside the laminate must not exceed some maximum value; and the cure process should be completed …

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 …

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.