VTechWorks Repository :: Browsing by Author "Hallauer, William L. Jr."

Browsing by Author "Hallauer, William L. Jr."

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Design of Gages for Direct Skin Friction Measurements in Complex Turbulent Flows with Shock Impingement Compensation
Rolling, August Jameson (Virginia Tech, 2007-06-07)
This research produced a new class of skin friction gages that measures wall shear even in shock environments. One test specimen separately measured wall shear and variable-pressure induced moment. Through the investigation of available computational modeling methods, techniques for accurately predicting gage physical responses were developed. The culmination of these model combinations was a design optimization procedure. This procedure was applied to three disparate test conditions: 1) short-duration, high-enthalpy testing, 2) blow-down testing, and 3) flight testing. The resulting optimized gage designs were virtually tested against each set of nominal load conditions. The finalized designs each successfully met their respective test condition constraints while maximizing strain output due to wall shear. These gages limit sources of apparent strain: inertia, temperature gradient, and uniform pressure. A unique use of bellows provided a protective shroud for surface strain gages. Oil fill provided thermal and dynamic damping while eliminating uniform pressure as a source of output voltage. Two Wheatstone bridge configurations were developed to minimize temperature effects first from temperature gradient and then from spatially varying heat flux induced gradient. An inertia limiting technique was developed that parametrically investigated mass and center of gravity impact on strain output. Multiple disciplinary computational simulations of thermal, dynamic, shear, moment, inertia, and instrumentation interaction were developed. Examinations of instrumentation error, settling time, filtering, multiple input dynamic response, and strain gage placement to avoid thermal gradient were conducted. Detailed mechanical drawings for several gages were produced for fabrication and future testing.
Design, Analysis, Fabrication, and Testing of a Nanosatellite Structure
Stevens, Craig L. (Virginia Tech, 2002-05-28)
The satellite industry is undergoing a transition toward "smallsat" engineering. Small satellites are becoming more attractive to customers as a method of decreasing cost. As the launch costs remain relatively constant, the industry is turning towards nano-technology, such as microelectromechanical systems, and distributed satellite systems to perform the same missions that once required super-satellites. Nanosatellites form one group of these high risk/low cost spacecraft. The Virginia Tech Ionospheric Scintillation Measurement Mission, known as HokieSat, is a 40 lb nanosatellite being designed and built by graduate and undergraduate students. The satellite is part of the Ionospheric Observation Nanosatellite Formation (ION-F) which will perform ionospheric measurements and conduct formation flying experiments. This thesis describes the design of the primary satellite structure, the analysis used to arrive at the design, the fabrication of the structure, and the experimentation used to verify the analysis. We also describe the internal and external configurations of the spacecraft and how we estimate the mass properties of the integrated satellite. The design of the spacecraft uses a composite laminate isogrid structure as a method of structural optimization. This optimization method is shown to increase the structural performance by over 20%. We conduct several finite element analyses to verify the structural integrity. We correlate these analyses with several static and modal tests to verify the models and the model boundary conditions. We perform environmental testing on the integrated spacecraft at NASA Wallops Flight Facility to investigate the properties of the structural assembly. Finally, we create a model of the ION-F stack to verify the integrity of the structure at the launch loads. We prove that the HokieSat structure will survive all environmental loads with no yielding or failures.
The effect of Whitcomb winglets and other wingtip modifications on wake vortices
Faery, Henry Frederick (Virginia Tech, 1977-06-05)
Wind tunnel experiments have been conducted on six different wingtip configurations to determine their wake vortex characteristics. The trailing wingtip vortex was probed by a 1/8 inch diameter five hole yawhead pressure probe in the VPI & SU Stability Wind Tunnel. The vortex tangential and axial velocity profiles are compared at five and twenty chord lengths downstream. Primary focus is placed on the Whitcomb winglet and its individual components, the upper winglet alone and the lower winglet alone. It is shown that the Whitcomb winglet and the upper winglet configuration both produce two distinct vortices of the same rotation. The maximum tangential velocity in each vortex is about 64 percent less than that produced by a conventional wingtip configuration. The axial velocity profiles exhibit strong velocity deficits throughout the vortex core. Aerodynamic force tests were conducted to compare the lift and drag characteristics of the wingtip configurations. Both the Whitcomb winglet and the upper winglet configuration have a remarkable ability to increase the lift-drag ratio and reduce the drag coefficient.
An exact plane-stress solution for a class of problems in orthotropic elasticity
Erb, David Alden (Virginia Tech, 1981-03-03)
An exact solution for the stress field within a rectangular slab of orthotropic material is found using a two-dimensional Fourier series formulation. The material is required to be in plane stress, with general stress boundary conditions, and the principle axes of the material must be parallel to the sides of the rectangle. Two load cases similar to those encountered in materials testing are investigated using the solution. The solution method developed is seen to have potential uses in stress analysis of composite structures.
Experimental-theoretical study of velocity feedback damping of structural vibrations
Skidmore, Gary R. (Virginia Polytechnic Institute and State University, 1985)
This study concerns the active damping of structural vibrations through the application of various forms of velocity feedback control. Active damping will be required for large space structures which are performance-sensitive to motion or inaccurate pointing. Several control forms, including modal-space active damping and direct rate feedback, are analyzed theoretically, and three laboratory models are described. A previous, unsuccessful attempt at control is reviewed and explained. The remaining control forms developed in the theoretical section were implemented successfully and the results compare favorably with theoretical predictions. Each control form is analyzed relative to its own merits and in comparison with other methods. An important point is the stability assured by a dual (colocated) configuration. of velocity sensors and control force actuators. Modal-space active damping is shown to be an effective control method with predictable performance in controlled modes and beneficial spillover into residual (non-controlled) modes.
Final Report: Second Forum on Space Structures
(Virginia Tech, 1984-06)
This document consists of summaries of presentations and discussions from the Forum, which was a meeting for investigators of structural dynamics and control issues in large space structures technology held 11-13 June 1984. The major issues considered are modeling of spacecraft structures, passive and active control techniques, integrated design of structure and control, and experiment and implementation (hardware related) topics, such as sensors, actuators, test techniques, etc. The current status of the technology is reviewed, deficiencies are identified, and recommendations for future research are made.
Introduction to Linear, Time-Invariant, Dynamic Systems for Students of Engineering
Hallauer, William L. Jr. (Virginia Tech, 2016-06-02)

This is a complete college textbook, including a detailed table of contents, seventeen chapters (each with a set of relevant homework problems), a list of references, two appendices, and a detailed index. The book is intended to enable students to: - Solve first-, second-, and higher-order, linear, time-invariant (LTI) ordinary differential equations (ODEs) with initial conditions and excitation, using both time-domain and Laplace-transform methods; - Solve for the frequency response of an LTI system to periodic sinusoidal excitation and plot this response in standard form; - Explain the role of the time constant in the response of a first-order LTI system, and the roles of natural frequency, damping ratio, and resonance in the response of a second-order LTI system; - Derive and analyze mathematical models (ODEs) of low-order mechanical systems, both translational and rotational, that are composed of inertial elements, spring elements, and damping devices; - Derive and analyze mathematical models (ODEs) of low-order electrical circuits composed of resistors, capacitors, inductors, and operational amplifiers; - Derive (from ODEs) and manipulate Laplace transfer functions and block diagrams representing output-to-input relationships of discrete elements and of systems; - Define and evaluate stability for an LTI system; - Explain proportional, integral, and derivative types of feedback control for single-input, single-output (SISO), LTI systems; - Sketch the locus of characteristic values, as a control parameter varies, for a feedback-controlled SISO, LTI system; - Use MATLAB as a tool to study the time and frequency responses of LTI systems. The book’s general organization - Chapters 1-10 deal primarily with the ODEs and behaviors of first-order and second-order dynamic systems; - Chapters 11 and 12 discuss the ODEs and behaviors of mechanical systems having two degrees of freedom, i.e., fourth-order systems; - Chapters 13 and 14 introduce classical feedback control; - Chapter 15 presents the basic features of proportional, integral, and derivative types of classical control; - Chapters 16 and 17 discuss methods for analyzing the stability of classical control systems. The general minimum prerequisite for understanding this book is the intellectual maturity of a junior-level (third-year) college student in an accredited four-year engineering curriculum. A mathematical second-order system is represented in this book primarily by a single second-order ODE, not in the state-space form by a pair of coupled first-order ODEs. Similarly, a two-degrees-of-freedom (fourth-order) system is represented by two coupled second-order ODEs, not in the state-space form by four coupled first-order ODEs. The book does not use bond graph modeling, the general and powerful, but complicated, modern tool for analysis of complex, multidisciplinary dynamic systems. The homework problems at the ends of chapters are very important to the learning objectives, so the author attempted to compose problems of practical interest and to make the problem statements as clear, correct, and unambiguous as possible. A major focus of the book is computer calculation of system characteristics and responses and graphical display of results, with use of basic (not advanced) MATLAB commands and programs. The book includes many examples and homework problems relevant to aerospace engineering, among which are rolling dynamics of flight vehicles, spacecraft actuators, aerospace motion sensors, and aeroelasticity. There are also several examples and homework problems illustrating and validating theory by using measured data to identify first- and second-order system dynamic characteristics based on mathematical models (e.g., time constants and natural frequencies), and system basic properties (e.g., mass, stiffness, and damping). Applications of real and simulated experimental data appear in many homework problems. The book contains somewhat more material than can be covered during a single standard college semester, so an instructor who wishes to use this as a one-semester course textbook should not attempt to cover the entire book, but instead should cover only those parts that are most relevant to the course objectives.
About the author
William L. Hallauer, Jr. is an Adjunct Professor in the Department of Aerospace and Ocean Engineering at Virginia Tech. Contact the author at usafadfemciv01@gmail.com Education: - B.S. in Mechanical Engineering, Stanford University, 1961-65; - S.M. in Aeronautics and Astronautics, Massachusetts Institute of Technology, 1965-66; - Ph.D. in Aeronautics and Astronautics, Stanford University, 1969-74.
Employment in higher education: - Virginia Polytechnic Institute and State University (Aerospace and Ocean Engineering, Mechanical Engineering), 1974-87, 1989-91, 2000-05; - United States Air Force Academy (Engineering Mechanics), 1987-89, 1994-99. Employment in industry: - Boeing Company (Commercial Airplane Group), 1966-69; - Lockheed Missiles and Space Company, 1973-74; - Dynacs Engineering Company, Inc. (contractor for the U.S. Air Force), 1992-94. Primary technical areas of learning, teaching, and research: - Structures, structural dynamics, and fluid-structure interaction (theory and computation); - Experimental analysis of structural dynamics, including electrical and electromechanical systems used in experiments; - Active control of vibration in highly flexible structures; - Composition of research articles and instructional material.
The simulation of surface ship micro-bubble wakes
Hyman, Mark C. (Virginia Tech, 1990-04-05)
A method in which the transport and evolution of the bubble population in a surface ship wake is numerically simulated is presented. The simulation is accomplished by constructing an advective-diffusive transport model for the scalar bubble field and solving this model for late times after ship passage. The bubble population model requires convection velocities and turbulent diffusion information that is supplied by solving the Reynolds-averaged parabolized Navier-Stokes equations with a k - ∊ turbulence model. The mean flow equations are solved by approximating the differential equations with a second order accurate finite difference scheme. The resulting large, sparse, banded matrix is solved by applying a version of the conjugate gradient method. The method has proven to be efficient and robust for the free shear flow problems of interest here. The simulation is initiated with given information in a plane at some point downstream of the ship from which the solution is propagated. The model is executed for a single and a twin propeller ship at 15 knots. The simulation shows that the development of the hydrodynamic and bubble near wake is dominated by ship geometry via strong advective transport. The far wake is dominated by diffusion and bubble rise and dissolution. Thus relatively large changes in geometry have a limited influence on the far wake.

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