Aerospace Engineering Commons^™

Control Of Vortical Separation On A Circular Cone, Nikos J. Mourtos

Faculty Publications

For conical bodies, at moderate angles of attack, the flow separates from the lee side, forming two vortices. Although the vortex lift contrihution is highly desirable, as the angle of attack increases, the vortex system becomes asymmetric, and eventually the vortices breakdown. Thus, some control of the separation process is necessary if the vortex lift is to be exploited at higher angles of attack. The theoretical model which is used in this analysis has three parts. First, the 'single line-vortex' model is used within the framework of 'slender-body theory' to compute the outer inviscid field for specified separation lines. Second, …

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 …

Parallel Implementation Of A Recursive Least Squares Neural Network Training Method On The Intel Ipsc/2, James Edward Steck, Bruce M. Mcmillin, K. Krishnamurthy, M. Reza Ashouri, Gary G. Leininger

Computer Science Faculty Research & Creative Works

An algorithm based on the Marquardt-Levenberg least-square optimization method has been shown by S. Kollias and D. Anastassiou (IEEE Trans. on Circuits Syst. vol.36, no.8, p.1092-101, Aug. 1989) to be a much more efficient training method than gradient descent, when applied to some small feedforward neural networks. Yet, for many applications, the increase in computational complexity of the method outweighs any gain in learning rate obtained over current training methods. However, the least-squares method can be more efficiently implemented on parallel architectures than standard methods. This is demonstrated by comparing computation times and learning rates for the least-squares method implemented …

Long-Range Planning Cost Model For Support Of Future Space Missions By The Deep Space Network, J. S. Sherif, Donald S. Remer, H. R. Buchanan

All HMC Faculty Publications and Research

A simple model is suggested to do long-range planning cost estimates for Deep Space Network (DSP) support of future space missions. The model estimates total DSN preparation costs and the annual distribution of these costs for long-range budgetary planning. The cost model is based on actual DSN preparation costs from four space missions: Galileo, Voyager (Uranus), Voyager (Neptune), and Magellan. The model was tested against the four projects and gave cost estimates that range from 18 percent above the actual total preparation costs of the projects to 25 percent below. The model was also compared to two other independent projects: …

Thermoelastic Problems Of Multilayered Cylinders, Victor Birman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Thermoelastic problems of long multilayered cylinders manufactured from isotropic materials are considered. The steady-state thermal field corresponding to a constant difference between temperature outside and inside the assembly is used in the analysis. Both the case of a hollow cylinder and that of a solid multilayered assembly are discussed. A closed-form exact solution is shown for an arbitrary number of layers if the properties of constituent materials remain unaffected by temperature. Various strategies leading to an analytical solution are proposed for the case where material properties depend on temperature. The stresses in a dual-coated optical fiber subject to a uniform …

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 …

Thermoelastic Problem Of A Thick Orthotopic Beam On Twodirectiooal Elastic Foundation, Victor Birman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The thermoelastic problem of an orthotropic beam supported by an elastic foundation which resists lateral deformations as well as displacements parallel to the beam axis is considered. The solution for a relatively thick beam is obtained based on the first-order shear deformation theory. The problem is reduced to- the solution of an ordinary seventh-order differential equation which can be obtained in the closed form. The case of a slender beam is treated as a particular case of a more general solution for a shear deformable beam. © 1990 ASME.

Thermal Dynamic Problems Of Reinforced Composite Cylinders, Victor Birman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Thermal dynamic problems of circular cylindrical composite shells reinforced in the axial and circumferential directions and subject to variations of temperature are considered. Nonlinear governing equations are formulated based on the extension of Donnell shell theory. These equations are used to determine the response of geometrically nonlinear and linear shells to a thermal loading represented by the Heaviside step function (thermal shock). The solution of the nonlinear problem obtained by the assumption that displacements are single-term functions of coordinates is discussed. The analysis of the linear problem illustrates different types of response to thermal shock. The condition of thermally induced …

Effect Of Viscoplastic Flow Rules On The Initiation And Growth Of Shear Bands At High Strain Rates, R. C. Batra, Chang-Soo Kim

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Marchand and Duffy have reported detailed measurements of the temperature and strain as a shear band develops in a HY-100 steel. Assuming their torsional tests in thin-wall tubes can be adequately modeled by a viscoplastic block undergoing overall adiabatic simple shearing deformations, we investigate the effect of modeling the viscoplastic response of the material by a.power law, and flow rules proposed by Litonski, Bodner and Partom, and Johnson and Cook. Each of these flow rules is first calibrated by using the test data at a nominal strain-rate of 3300 s-1. Then predictions from the use of these flow rules at …

Planning Optimal Robot Trajectories By Cell Mapping, W. H. Zhu, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A cell-mapping method is introduced for planning global trajectories of robotic manipulators in cases where the cell space is composed of combination pairs of plane cells. With the proposed method, optimal trajectory problems in the free field and in the obstacle-constrained field are studied. Two numerical examples are given to show the obtained optimal trajectories and controls.

Robust Nonlinear Control Of Brushless Dc Motors In The Presence Of Magnetic Saturation, N. Hemati, J. S. Thorp, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A robust control law is derived and examined for a direct-drive robot arm driven by a brushless DC motor (BLDCM). The complete dynamics of the motor and its interaction with the robot arm are accounted for. This is important, since in a direct-drive servo system the torque generated by the motor is directly transmitted to the load. Effects of magnetic saturation as well as reluctance variations are accounted for, in order to ensure accuracy. The effectiveness of the method is examined through computer simulations. The computational complexity of the overall control scheme is such that it can be readily used …

Use Of Energy In Data-Track Association And State Estimation In Multitarget-Multisensor Problems, S. N. Balakrishnan, H. Park

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A coarse test and a fine test have been formulated for use in multiple sensor-multiple target data-track association. Various forms of energies are used in these tests to pick the proper data to be associated with any target. Numerical experiments which involve the use of a decentralized Kalman filter scheme are presented. The experiments show the effectiveness of the two tests

A Complete Model Characterization Of Brushless Dc Motors, N. Hemati, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The modeling problem associated with brushless DC motors (BLDCMs) with nonuniform air gaps which operate in a range where magnetic saturation may exist is addressed. The mathematical model, includes the effects of reluctance variations and magnetic saturation to guarantee proper modeling of the system. An experimental procedure is developed and implemented in a laboratory environment to identify the electromagnetic characteristics of a BLDCM in the presence of magnetic saturation. It is demonstrated that the modeling problem associated with this class of BLDCM can be formulated in terms of mathematically modeling a set of multidimensional surfaces corresponding to the electromagnetic torque …

An Extension Of Essentially Non-Oscillatory Shock-Capturing Schemes To Multi-Dimensional Systems Of Conservation Laws, Jay Casper

Mathematics & Statistics Theses & Dissertations

In recent years, a class of numerical schemes for solving hyperbolic partial differential equations has been developed which generalizes the first-order method of Godunov to arbitrary order of accuracy. High-order accuracy is obtained, wherever the solution is smooth, by an essentially non-oscillatory (ENO) piecewise polynomial reconstruction procedure, which yields high-order pointwise information from the cell averages of the solution at a given point in time. When applied to piecewise smooth initial data, this reconstruction enables a flux computation that provides a time update of the solution which is of high-order accuracy, wherever the function is smooth, and avoids a Gibbs …

Combined Solar And Internal Load Effects On Selection Of Heat Reclaim-Economizer Hvac Systems, Harry J. Sauer, Ronald Hunter Howell, Zijie Wang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The concern for energy conservation has led to the development and use of heat recovery systems which reclaim the building internal heat before it is discarded in the exhaust air. On the other hand, economizer cycles have been widely used for many years in a variety of types of HVAC systems. Economizer cycles are widely accepted as a means to reduce operating time for chilling equipment when cool outside air is available. It has been suggested that heat reclaim systems should not be used in conjunction with an HVAC system which incorporates an economizer cycle because the economizer operation would …

Robust Nonlinear Control Of Brushless Dc Motors For Direct-Drive Robotic Applications, N. Hemati, J. S. Thorp, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The control problem associated with brushless DC motors (BLDCMs) for direct-drive robotic applications is considered. In order to guarantee the high-performance operation of BLDCMs in such applications, the effects of reluctance variations and magnetic saturation are accounted for in the model. Such a BLDCM model constitutes a highly coupled and nonlinear dynamic system. Using the transformation theory of nonlinear systems, a feedback control law, which is shown to compensate for the system nonlinearities, is derived. Conditions under which such a control law is possible are presented. The need for the derivation of explicit commutation strategies is eliminated, resulting in reduction …

A Differential Equation Approach To Swept Volumes, Ming-Chuan Leu, Denis Blackmore

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An approach to the analysis of swept volumes is introduced. It is shown that every smooth Euclidean motion or sweep, can be identified with a first-order, linear, ordinary differential equation. This sweep differential equation provides useful insights into the topological and geometrical nature of the swept volume of an object. A certain class, autonomous sweeps, is identified by the form of the associated differential equation, and several properties of the swept volumes of the members of this class are analyzed. The results are applied to generate swept volumes for a number of objects. Implementation of the sweep differential equation approach …

A Study Of The Hydration Properties Of Selected Laser Dye Aerosols Including Continuous-Flow Parallel Plate And Alternating-Gradient Thermal Diffusion Cloud Chamber Measurements In The High Supersaturation Regime, Donald E. Hagen, Max B. Trueblood, Darryl J. Alofs

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The Hydration Behavior of Aerosols made Up of Various Fluorescent Dyes when Exposed to Water Saturation or Supersaturated Conditions Has Been Studied. Critical Supersaturation Spectra Are Reported. the Dyes Are Found to Behave as High Molecular Weight Ionic Compounds that Obey Kohler Theory. their Relevant Kohler Parameters Are Measured. This Study Makes Use of and Compares Results from the Isothermal Hazecontinuous-Flowand Alternating-Gradient Thermal Diffusion Cloud Chambers. the Ability of the Continuous-Flow Thermal Diffusion Chamber to Operate Correctly at High Supersaturations is Shown. © 1990 Elsevier Science Publishing Co., Inc.