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Browsing University Libraries by Department "Aerospace and Ocean Engineering"
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- 50-kHz-rate 2D imaging of temperature and H2O concentration at the exhaust plane of a J85 engine using hyperspectral tomographyMa, Lin; Li, Xuesong; Sanders, Scott T.; Caswell, Andrew W.; Roy, Sukesh; Plemmons, David H.; Gord, James R. (Optical Society of America, 2013-01-01)This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows. (C) 2013 Optical Society of America
- Introduction to Linear, Time-Invariant, Dynamic Systems for Students of EngineeringHallauer, 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. - Laser Displacement Sensors for Wind Tunnel Model Position MeasurementsKuester, Matthew; Intaratep, Nanyaporn; Borgoltz, Aurelien (MDPI, 2018-11-22)Wind tunnel measurements of two-dimensional wing sections, or airfoils, are the building block of aerodynamic predictions for many aerodynamic applications. In these experiments, the forces and pitching moment on the airfoil are measured as a function of the orientation of the airfoil relative to the incoming airflow. Small changes in this angle (called the angle of attack, or α ) can create significant changes in the forces and moments, so accurately measuring the angle of attack is critical in these experiments. This work describes the implementation of laser displacement sensors in a wind tunnel; the sensors measured the distance between the wind tunnel walls and the airfoil, which was then used to calculate the model position. The uncertainty in the measured laser distances, based on the sensor resolution and temperature drift, is comparable to the uncertainty in traditional linear encoder measurements. Distances from multiple sensors showed small, but statistically significant, amounts of model deflection and rotation that would otherwise not have been detected, allowing for an improved angle of attack measurement.
- Numerical and experimental validation of a three-dimensional combustion diagnostic based on tomographic chemiluminescenceCai, Weiwei; Li, Xuesong; Li, Fei; Ma, Lin (Optical Society of America, 2013-03-25)Three-dimensional (3D) measurements are highly desirable both for fundamental combustion research and practical monitoring and control of combustion systems. This work discusses a 3D diagnostic based on tomographic chemiluminescence (TC) to address this measurement need. The major contributions of this work are threefold. First, a hybrid algorithm is developed to solve the 3D TC problem. The algorithm was demonstrated in extensive tests, both numerical and experimental, to yield 3D reconstruction with high fidelity. Second, an experimental approach was designed to enable quantifiable metrics for examining key aspects of the 3D TC technique, including its spatial resolution and reconstruction accuracy. Third, based on the reconstruction algorithm and experimental results, we investigated the effects of the view orientations. The results suggested that for an unknown flame, it is better to use projections measured from random orientations than restricted orientations (e.g., coplanar orientations). These findings are expected to provide insights to the fundamental capabilities of the TC technique, and also to facilitate its practical application.
- Predicting the combined effect of multiple genetic variantsLiu, Mingming; Watson, Layne T.; Zhang, Liqing (2015-07-30)Background Many genetic variants have been identified in the human genome. The functional effects of a single variant have been intensively studied. However, the joint effects of multiple variants in the same genes have been largely ignored due to their complexity or lack of data. This paper uses HMMvar, a hidden Markov model based approach, to investigate the combined effect of multiple variants from the 1000 Genomes Project. Two tumor suppressor genes, TP53 and phosphatase and tensin homolog (PTEN), are also studied for the joint effect of compensatory indel variants. Results Results show that there are cases where the joint effect of having multiple variants in the same genes is significantly different from that of a single variant. The deleterious effect of a single indel variant can be alleviated by their compensatory indels in TP53 and PTEN. Compound mutations in two genes, β-MHC and MyBP-C, leading to severer cardiovascular disease compared to single mutations, are also validated. Conclusions This paper extends the functionality of HMMvar, a tool for assigning a quantitative score to a variant, to measure not only the deleterious effect of a single variant but also the joint effect of multiple variants. HMMvar is the first tool that can predict the functional effects of both single and general multiple variations on proteins. The precomputed scores for multiple variants from the 1000 Genomes Project and the HMMvar package are available at https://bioinformatics.cs.vt.edu/zhanglab/HMMvar/
- Prediction of Dynamic Stability Using Mapped Chebyshev Pseudospectral MethodChoi, Jae-Young; Im, Dong Kyun; Park, Jangho; Choi, Seongim Sarah (Hindawi, 2018-08-01)A mapped Chebyshev pseudospectral method is extended to solve three-dimensional unsteady flow problems. As the classical Chebyshev spectral approach can lead to numerical instabilities due to ill conditioning of the spectral matrix, the Chebyshev points are evenly redistributed over the domain by an inverse sine mapping function. The mapped Chebyshev pseudospectral method can be used as an alternative time-spectral approach that uses a Chebyshev collocation operator to approximate the time derivative terms in the unsteady flow governing equations, and the method can make general applications to both nonperiodic and periodic problems. In this study, the mapped Chebyshev pseudospectral method is employed to solve three-dimensional periodic problem to verify the spectral accuracy and computational efficiency with those of the Fourier pseudospectral method and the time-accurate method. The results show a good agreement with both of the Fourier pseudospectral method and the time-accurate method. The flow solutions also demonstrate a good agreement with the experimental data. Similar to the Fourier pseudospectral method, the mapped Chebyshev pseudospectral method approximates the unsteady flow solutions with a precise accuracy at a considerably effective computational cost compared to the conventional time-accurate method.
- Recent Remote Sensing Innovations and Future DirectionThomas, Valerie A.; Wynne, Randolph H.; Liknes, Greg C.; Derwin, Jill M.; Coulston, John W.; Brooks, Evan B.; Finco, Mark V.; Saxena, R.; Watson, Layne T.; Moisen, G. G.; Ruefenacht, Bonnie; Megown, Kevin (2017-10-25)
- Single-shot volumetric laser induced fluorescence (VLIF) measurements in turbulent flows seeded with iodineWu, Yu; Xu, Wejiang; Lei, Qingchun; Ma, Lin (OSA, 2015-12-17)This work reports the experimental demonstration of single-shot visualization of turbulent flows in all three spatial dimensions (3D) based on volumetric laser induced fluorescence (VLIF). The measurements were performed based on the LIF signal of iodine (I₂) vapor seeded in the flow. In contrast to established planar LIF (PLIF) technique, the VLIF technique excited the seeded I₂ vapor volumetrically by a thick laser slab. The volumetric LIF signals emitted were then simultaneously collected by a total of five cameras from five different orientations, based on which a 3D tomographic reconstruction was performed to obtain the 3D distribution of the I₂ vapor in the target flow. Single-shot measurements (with a measurement duration of a few ns) were demonstrated in a 50 mm × 50 mm × 50 mm volume with a nominal spatial resolution of 0.42 mm and an actual resolution of ~0.71 mm in all three dimensions (corresponding to a total of 120 × 120 × 120 voxels).
- Volumetric imaging of turbulent reactive flows at kHz based on computed tomographyLi, Xuesong; Ma, Lin (OSA Publishing, 2014-02-21)Diagnostics with three-dimensional (3D) spatial resolution and rapid temporal resolution have been long desired to resolve the complicated turbulence-chemistry interactions. This paper describes a method based on based on tomographic chemiluminescence (TC) to address this diagnostic need. The TC technique used multiple cameras to simultaneously record CH* chemiluminescence emitted by turbulent flames from different view angles. A 3D tomographic algorithm was then applied to reconstruct the instantaneous flame structures volumetrically. Both experimental and computational studies have been conducted to demonstrate and validate the 3D measurements. Experimental results were obtained instantaneously at kHz temporal rate, in a volume of 16 × 16 × 16 cm3, and with a spatial resolution estimated to be 2~3 mm. Computations were conducted to simulate the experimental conditions for comparison and validation.