Engineering Commons^™

Variational Methods In Sensitivity Analysis And Optimization For Aerodynamic Applications, Adem Ibrahim Hussen

Mechanical & Aerospace Engineering Theses & Dissertations

Variational methods (VM) sensitivity analysis, which is the continuous alternative to the discrete sensitivity analysis, is employed to derive the costate (adjoint) equations, the transversality conditions, and the functional sensitivity derivatives. In the derivation of the sensitivity equations, the variational methods use the generalized calculus of variations, in which the variable boundary is considered as the design function. The converged solution of the state equations together with the converged solution of the costate equations are integrated along the domain boundary to uniquely determine the functional sensitivity derivatives with respect to the design function.

The determination of the sensitivity derivatives of …

An Investigation Into The Effects Of Lateral Aerodynamic Asymmetries, Lateral Weight Asymmetries, And Differential Stabilator Bias On The F-15 Directional Flight Characteristics At High Angles Of Attack, David R. Evans

Theses and Dissertations

The F-15 is a stable aircraft throughout most of its flight envelope. However, it still exhibits an uncommanded yawing and rolling tendency at high angles-of-attack. Identified influencing factors of this uncommanded motion are lateral aerodynamic asymmetries, lateral weight asymmetries, and differential stabilator bias. Previous research into the effects of these influencing factors has been qualitative. This thesis quantifies the effects and then identifies a symmetric F-15 configuration. The quantifying metric presented is net yaw acceleration. This thesis used both computer simulation and experimental flight test to quantify these effects. A discussion of each influencing factors effects on the F-15B high …

International Space Station Traffic Modeling And Simulation, Jillene B. Rylaarsdam

Theses and Dissertations

In an effort to provide NASA with an alternative perspective and some insights to the operational planning of the International Space Station (ISS), this research developed a simulation environment for the ISS and devised a method to evaluate various altitude strategies. The simulation environment allowed us to incorporate the natural random behaviors which affect the lifetime of objects in low earth orbit. We created prototype models of the operational planning process to analyze current altitude strategy approaches and acquire new strategies from insights observed. In addition, by extrapolating random future solar activity values from the interpolation of historical data, we …

Structural Damage Identification From Limited Measurement Data, Richard G. Cobb

Theses and Dissertations

The research focused on the development of a new method to identify damaged structural elements from a large flexible space structure on-orbit, using limited measured modal data. Limited measured modal data is loosely defined as measured data containing only a few modal frequencies and less than 10% of the total structural degrees-of-freedom. This effort was decomposed into four specific tasks. The first is the identification of partial modal properties from measured data of the nominal space structure. Second, the finite element model must be adjusted to match the measured nominal partial data. The third task is an analysis of the …

Modeling Of Progressive Damage In Fiber-Reinforced Ceramic Matrix Composites, James P. Solti

Theses and Dissertations

An analytic methodology is developed to model the response of fiber-reinforced ceramic matrix composites (CMOs) when subjected to monotonic and fatigue loadings. The analysis requires the formulation of (1) a micromechanics model which defines the laminate's geometry and constitutive relationship; (2) failure criteria which estimate the extent of microstructural damage, and, finally, (3) a means of analyzing frictional slip, fiber pull-out, interfacial wear and laminate failure. For the present study, the behavior of unidirectional and crossply CMOs is investigated using modified shear-lag theory in conjunction with a set of failure criteria with a minimum reliance on empirical data. The damage …

Compressible Turbulence Measurements In A Supersonic Boundary Layer With Impinging Shock Wave Interaction, Michael J. Meyer

Theses and Dissertations

No abstract provided.

Comparison Of The Control Anticipation Parameter And The Bandwidth Criterion During The Landing Task, David A. Kivioja

Theses and Dissertations

Many handling qualities criteria have been developed which predict pilot opinion of landing aircraft. MIL-STD-1797A, 'Flying Qualities of Piloted Aircraft' lists six different criteria. However, applying all six criteria to one aircraft can lead to conflicting results. The Air Force Institute of Technology (AFIT) along with the Flight Dynamics Laboratory have conducted research to evaluate differences among the handling qualities criteria in MIL-STD-1797A. The overall objective of this thesis was to determine similarities and discrepancies between the Control Anticipation Parameter (CAP) and bandwidth criteria, and to evaluate the advantage of including a dropback criterion with the bandwidth criterion. Results of …

Riblet Effects On Gortler Vortex Development Over A Concave Surface, James A. Rothenflue

Theses and Dissertations

Riblet effects on Goertler vortex development in laminar and transitional flows were measured using three-dimensional laser-Doppler anemometry. Three freestream velocities were tested such that riblet spacing corresponded to Goertler vortex (GV) wavelengths which presumably would be either strongly amplified, weakly amplified, or attenuated by centrifugal forces on a curved surface. Experiments revealed the development of paired, counterrotating vortices within the riblet valleys over both flat and concave surfaces. For riblet spacings equivalent to weakly or non-amplified GV wavelengths, GV development on a curved surface was above the riblets and was delayed by the addition of riblets. The GV wavelength was …

A Finite Element Model Of Thermoacoustic Oscillations In Rayleigh Flow, Carlos A. Gutierrez, Walter Eversman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The work reported here describes a portion of the development of a finite element model of thermoacoustic oscillations in ducted flows, including three dimensional geometries and nonuniform mean flows with steady heat addition. The thermoacoustic problem is not modeled by a form of the convected wave equation but instead by the conservation equations in primitive form. In this paper the three-dimensional model is reduced to one dimension, applicable to a uniform geometry, but allowing an axially nonuniform flow with sharp gradients in temperature, density, and Mach number. The steady mean flow is computed as a Rayleigh flow. Calculations are shown …

A New Pre-Loaded Membrane Geometric Stiffness Matrix With Full Rigid Body Capabilities, Paul A. Bosela, D. R. Ludwiczak

Civil and Environmental Engineering Faculty Publications

Space structures, due to economic considerations, must be light-weight. Accurate prediction of the natural frequencies and mode shapes is critical for determining the structural adequacy of components, and designing a control system. The total stiffness of a member, in many cases, includes both the elastic stiffness of the material as well as additional geometric stiffness due to pre-load (initial stress stiffness). The pre-load causes serious reservations on the use of standard finite element techniques of solution. In particular, a phenomenon known as ''grounding'', or false stiffening, of the stiffness matrix occurs during rigid body rotation. The author has previously shown …

Cost Scale-Up Factors For Airport Construction, Donald S. Remer, Christopher Wong '96

All HMC Faculty Publications and Research

Engineers must often make a quick "ballpark" cost estimate of a new plant, facility, or piece of equipment before the detailed design phase. One easy way to obtain such an estimate is to base the cost on a known cost for a similar plant, facility, or piece of equipment by using the ratio of the capacities or sizes of the known and proposed item raised to an exponent R. This predesign cost-estimating approach is especially useful for doing sensitivity analyses and feasibility studies for which a high degree of accuracy is not required. This cost-capacity or power-factor model was …

A Dual Neural Network Architecture For Linear And Nonlinear Control Of Inverted Pendulum On A Cart, S. N. Balakrishnan, Victor Biega

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The use of a self-contained dual neural network architecture for the solution of nonlinear optimal control problems is investigated in this study. The network structure solves the dynamic programming equations in stages and at the convergence, one network provides the optimal control and the second network provides a fault tolerance to the control system. We detail the steps in design and solve a linearized and a nonlinear, unstable, four-dimensional inverted pendulum on a cart problem. Numerical results are presented and compared with linearized optimal control. Unlike the previously published neural network solutions, this methodology does not need any external training, …

A Class Of Modified Hopfield Networks For Aircraft Identification And Control, Jie Shen, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This paper presents a class of modified Hopfield neural networks and their use in solving aircraft optimal control and identification problems. This class of networks consists of parallel recurrent networks which have variable dimensions that can be changed to fit the problems under consideration. It has a structure to implement an inverse transformation that is essential for embedding optimal control gain sequences. Equilibrium solutions are discussed. Energy minimization of the networks leads to identification of the system parameters. Numerical results are provided to identify the dynamics of an aircraft, and the corresponding optimal control is calculated online. Comparison of the …

Heat Transfer In Two-Phase Solid-Rocket Plumes, Harlan F. Nelson, John C. Fields

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Results of a direct simulation Monte Carlo (DSMC) and free molecule (FM) analysis of convective heat transfer to Al2O3 particles in solid-rocket plume environments are presented. The particle diameters are assumed to be 4μm, and the plume gases are CO2, H2O, CO, and N2. The plume gas temperature is 2000 K. Particle temperatures of 1500, 2000, and 2500 K are investigated for Knudsen numbers from 1/2 to 1000 (from slip flow to FM flow). The Nusselt number is presented in terms of Knudsen number and Reynolds number (or relative velocity). Both the Kavanau and the Kashmarov and Svirshevskii correlations generally …

Effect Of Inflow Pressure And Wall Heat Transfer On Shock-Induced Combustion/Detonation, B. S. Green, Harlan F. Nelson

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Oblique detonation waves are possible ignition mechanisms for scramjet engines. Results from a numerical study of the effects of changing the inflow pressure on oblique detonation wave structure for supersonic flow of a stoichiometric hydrogen-air mixture over a flat plate followed by a ramp are presented. Viscous effects and finite-rate chemistry are considered. Inflow pressure is varied from 0.1 to 1 atmosphere for Mach 4 inflow over a 30-degree ramp. Also, the effect of wall heat transfer rate is examined by comparing adiabatic wall, and constant temperature wall solutions. A separation bubble forms at the intersection of the flat plate …

Optimization For Maximum Performance High-Speed Engines, David W. Riggins

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Fuel-air combustion and the generation of irreversibility in high-speed flows are described in terms of the fundamental principles of nonequilibrium, work availability, and entropy increases. Engine thrust is analytically related to the overall engine irreversibility and the degree of combustion: Issues involving mixing enhancement assessment and engine optimization are then formalized and clarified. The concept of thrust-potential, as used in engine design and optimization, is shown to be a consistent application of the principles and findings of this and related investigations. This work was supported through NASA Grant NAG 1-1189. Special thanks are due to Charles McClinton at NASA Langley …

Hamiltonian Based Adaptive Critics For Missile Guidance, S. N. Balakrishnan, Jie Shen

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A Hamiltonian based adaptive critic structure is proposed for solving missile guidance problems. This structure consists of a supervisor neural network called 'critic' and a controller network called 'action'. Together they are used to solve model-based guidance problems. The advantage of this approach is that: i) the training data for each network is created by the other network, ii) the converged solutions yield near optimal guidance over the entire span of the training range, and iii) they can be used as feedback controllers though trained off-line. A main contribution is that we establish a direct link between traditional optimal control …

Target Profile Estimation Using Haar Functions, William R. Bockman, S. N. Balakrishnan, Christopher D'Souza, James Cloutier

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An approach to estimating the target acceleration in a maneuvering target model using Haar function partial summations to model the target acceleration is developed. A kinematic constraint is applied to the maneuvering target model and the effects of the use of this constraint are reviewed.

Non-Axisymmetric Matrix Cracking And Interface Debonding With Friction In Ceramic Composites, F. S. Ji, Lokeswarappa R. Dharani

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An three-dimensional analytical model based on the principle of minimum potential energy is developed and applied to determine the stress state in a discrete fiber/matrix composite cylinder subjected to axial tensile loading in the fiber direction and containing a non-symmetric transverse matrix crack and an interface debond. The friction over the debonded interface is incorporated into the analysis. The strain energy release rates associated with the matrix crack and the interface debonding under the combination of the applied load and the interface frictional force are computed. The strain energy release rate criterion has been employed to evaluate the critical applied …

Global Characteristics And Structure Of Hydrogen-Air Counterflow Diffusion Flames, J. Zhao, Kakkattukuzhy M. Isaac, G. L. Pellett

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A model based on similarity transformation, for the nitrogen-diluted, H2-air opposed-jet laminar counterflow diffusion flame (CFDF), was developed independently of earlier models, and numerically solved to study flame location and flame structure and extinction limits. Numerical stiffness is handled by a special treatment of the species production term. Flame location with respect to the stagnation plane is identified as an important parameter that governs H2-air diffusion flames, and physical explanations are given to show how flame location is affected by fuel dilution, strain rate, and Lewis number. Results show very good agreement with experimental extinction conditions. The effect of thermal …

Gas And Liquid Phase Transport In Pulsed Fuel Sprays, Pete D. Jennings, James A. Drallmeier

Mechanical and Aerospace Engineering Faculty Research & Creative Works

An infrared extinction technique was used to characterize spatially and temporally the vapor phase of a transient fuel spray. Optical extinction data were taken at two laser wavelengths and compared to obtain fuel vapor partial pressure values averaged over the line-of-sight through the spray. A transient fuel injector spray was characterized at several axial positions with a spatial resolution of 0.125 cm and a temporal resolution of 0.2 ms. With the knowledge of an axisymmetric spray pulse, the line-of-sight averaged results were deconvoluted to obtain spatially resolved vapor pressure data. The same spray was also characterized using phase/doppler interferometry to …

Radiative Heating In Scramjet Combustors, Harlan F. Nelson

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Currently, there is considerable interest in scramjet engines for hypersonic aircraft and missiles. This paper presents preliminary calculations of the radiative heating of the walls of scramjet combustion chambers. The analysis assumes isothermal, constant property flow fields which are representative of actual combustor flow fields. The fuel is H2 and N2 is taken as inert. Temperature in the combustor is on the order of 2000 to 3000 K and pressure is of the order of 5 atm. The combustion products consist mainly of H2O and OH. These gases are strong radiators in the infrared. Radiation heating can be significant because …

Dynamic Scale Genetic Algorithm: An Enhanced Genetic Search For Discrete Optimization, Bela Dange Joshi

Engineering Management & Systems Engineering Theses & Dissertations

The minimization of operations and support resources of reusable launch vehicles is a complex task, involving discrete optimization and the simulation domain. Genetic algorithms, offering a robust search strategy suitable for integer variables and the simulation domain, can be applied to minimize these resources. This research developed an enhanced genetic algorithm for problems with a linear objective function, the most common class of discrete optimization problems. The dynamic scale genetic algorithm developed here incorporates concepts of implicit enumeration to enhance search. This is achieved by utilizing problem specific information to refine the solution space over successive generations. The utility of …

The Modeling Of Structural-Acoustic Interaction Using Coupled Fe/Be Method And Control Of Interior Acoustic Pressure Using Piezoelectric Actuators, Yucheng Shi

Mechanical & Aerospace Engineering Theses & Dissertations

A coupled finite element (FE) and boundary element (BE) approach is presented to model full coupled structural/acoustic/piezoelectric systems. The dual reciprocity boundary element method is used so that the natural frequencies and mode shapes of the coupled system can be obtained, and to extend this approach to time dependent problems. The boundary element method is applied to interior acoustic domains, and the results are very accurate when compared with limited exact solutions. Structural--acoustic problems are then analyzed with the coupled finite element/boundary element method, where the finite element method models the structural domain and the boundary element method models the …

Numerical Simulation Of Complex, Three-Dimensional, Turbulent-Free Jets, Robert V. Wilson

Mechanical & Aerospace Engineering Theses & Dissertations

Three-dimensional, incompressible turbulent jets with rectangular and elliptical cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at low Reynoids numbers, whereas at high Reynolds numbers filtered forms of the equations are solved along with a sub-grid scale model to approximate the effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Although such methods are widely used in the simulation of compressible flows, the lack of an evolution equation for pressure or density presents particular difficulty in incompressible …

Comparison Of The Ralph Smith And The Time Domain Flying Qualities Criteria, Lori A. Carlucci

Theses and Dissertations

Aircraft pitch response is a crucial element of piloted vehicle flying qualities. The short term pitch response has created controversy over the form and substance of any requirements. Currently there are six different methods for evaluation in MIL-STD-1797A. There are many other methods which have been proposed. The biggest problem is that many of these methods often give conflicting results. The overall goal of the present effort is to compare and contrast the Time Domain criterion and the Ralph Smith criterion. By examining these methods on common grounds, areas of agreement and discrepancies can be found. Parametric studies are performed …

Investigation Of Residual Strength And Fatigue Life Of Unstiffened Aluminum Panels With Multiple Site Damage, Mark C. Cherry

Theses and Dissertations

Multiple Site Damage MSD is the occurrence of small fatigue cracks at several sites within aircraft structures. This is important since it may lower the residual strength and fatigue life of the structure beyond what can be predicted using the damage tolerance technique based on a single crack, currently in use to design aircraft structures. This study investigated the effects of MSD on unstiffined panels. MSD usually occurs at rivet holes, or other stress concentration locations within an aircraft structure. This study simulated rivet holes with MSD, by using holes of constant diameter with small cracks, evenly spaced across the …

An Experimental Investigation Of A Sting-Mounted Finite Circulation Control Wing, Lorenzo C. Bradley Iii

Theses and Dissertations

This study investigated the lift, drag and pitching moment performance of a circulation control wing in the AFIT 5-ft wind tunnel. The experimental wing model was a 20 percent thick, 8.5 percent camber, partial elliptical cross-section, single blowing slot, rectangular planform wing. The aspect ratios tested were 3.99, 3.77 and 3.75. The variables in the investigation included the slot blowing rate and model configuration. The model was modified by adding a leading edge nose droop, a trailing edge splitter plate and wing tip fences to improve flow at the leading edge, reduce separation effects, and encourage attached flow on the …

Thermo-Mechanical Fatigue Behavior Of Cross-Ply Ceramic Matrix Composite Under Tension-Tension Loading, Dana G. Allen

Theses and Dissertations

The purpose of this study was to investigate the combined effect of cyclic temperature and loading on the fatigue life of a ceramic matrix composite with a cross ply lay-up. The material used in this study was a potassium borosilicate glass (BSG) doped magnesium aluminosilicate (MAS) cordierite matrix reinforced with Nicalon (silicon carbide, SiC) fibers in a [0/90]_4s lay-up. Thermomechanical fatigue (TMF) tests were performed with a period of 180 seconds/cycle, or 0.00556 Hz, and a triangular wave-form. The temperature was cycled between 566°C and l093°C, and the stress levels varied between 60 MPa and 145 MPa. All tests …

Stress/Strain Ratio Effects On Fatigue Response Of A Scs-6/Ti-15-3 Metal Matrix Composite At Elevated Temperature, Sean C. Jackson

Theses and Dissertations

This study investigated the fatigue life and damage mechanisms of a [0]₈, SCS-6/Ti-15-3, metal matrix composite at 427°C for three different stress/strain ratios, R = -1, 0 and 0.5. Fatigue life and damage mechanism comparisons were made for the varying R ratios and between the load and strain control modes. Fatigue life comparisons show that on a maximum stress/strain basis as R is increased fatigue life increases while on a stress/strain range basis as R increases fatigue life decreases. Similar damage mechanisms were found between the R = -1 and R = 0 tests conducted at the same …