Aerospace Engineering Commons^™

A New Filtering Technique For A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In this paper, a new nonlinear filtering technique (θ-D filter) is presented. This filter is derived by constructing the dual of a new nonlinear regulator control technique, θ-D approximation which involves approximate solution to the Hamilton-Jacobi-Bellman equation. The structure of this filter is similar to the state dependent riccati equation filter (SDREF). However, this method does not need time-consuming online computation of the algebraic Riccati equation at each sample time compared with the SDREF. By manipulating the perturbation terms both the asymptotic stability and optimality properties can be obtained. A simple pendulum problem is investigated to demonstrate the effectiveness of …

State-Constrained Agile Missile Control With Adaptive-Critic-Based Neural Networks, Dongchen Han, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In this study, we develop an adaptive-critic-based controller to steer an agile missile that has a constraint on the minimum flight Mach number from various initial Mach numbers to a given final Mach number in minimum time while completely reversing its flightpath angle. This class of bounded state space, free final time problems is very difficult to solve due to discontinuities in costates at the constraint boundaries. We use a two-neural-network structure called "adaptive critic" in this study to carry out the optimization process. This structure obtains an optimal controller through solving optimal control-related equations resulting from a Hamiltonian formulation. …

Active And Adaptive Flow Control Of Twin-Tail Buffet And Applications, Zhi Yang

Mechanical & Aerospace Engineering Theses & Dissertations

Modern fighter aircraft with dual vertical tails are operated at high angles of attack. The vortex generated by leading edge extension (LEX) breaks down before reaching the two vertical tails. The wake of highly unsteady, turbulent flow causes unbalanced broadband aerodynamic loading on the tails and may produce severe buffet on the tails and lead to tail fatigue failure.

Flow suction along the vortex cores (FSVC) is investigated as an active control method for tail-buffet alleviation. Suction tubes have been tilted at different angles to study the control effectiveness of suction tubes orientation. Flow field response, aerodynamic loading and aeroelastic …

Pressure And Flow Validation Of A Second Generation Gas Extraction Probe For A Hybrid Rocket Gas Extraction System, Constance Meadors, Andrew B. Wright

Journal of the Arkansas Academy of Science

A gas extraction system (GES) has been designed for use with the hybrid rocket facility at the University of Arkansas at Little Rock (UALR) for spectroscopic analysis of rocket plumes. While monitoring gas flow-rate and pressure, the GES extracts gases from the hybrid rocket plume and transports them to a mass spectrometer. This paper describes design and construction of a gas extraction probe (GEP) prototype capable of extracting gases directly from the plume. Gas dynamics equations were used to design two venturi-type GEP, converging and converging-diverging. The probe was tested with air to verify design assumptions. Flow rate through the …

Supersonic Combustion And Mixing Characteristics Of Hydrocarbon Fuels In Screamjet Engines, Ahmed A. Taha

Mechanical & Aerospace Engineering Theses & Dissertations

The combustion characteristics of gaseous propane in supersonic airflow using the rearward-facing step that is swept inward from both end sides is studied. The effect of sweeping the step on the flow field features of propane combustion is investigated.

The study of the supersonic combustion of ethylene is carried out using different combustor configurations, different main fuel equivalence ratios, and different pilot fuel equivalence ratios.

The swept step shows the ability to hold the propane flame in the supersonic air stream without extinction. It was found that the side sweeping of the combustor exhibits the high temperature and combustion products …

Advances In Space Radiation Shielding Codes, John W. Wilson, Ram K. Tripathi, Garry D. Qualls, Francis A. Cucinotta, Richard E. Prael, John W. Norbury, John H. Heinbockel, John Tweed, Giovanni De Angelis

Mathematics & Statistics Faculty Publications

Early space radiation shield code development relied on Monte Carlo methods and made important contributions to the space program. Monte Carlo methods have resorted to restricted one-dimensional problems leading to imperfect representation of appropriate boundary conditions. Even so, intensive computational requirements resulted and shield evaluation was made near the end of the design process. Resolving shielding issues usually had a negative impact on the design. Improved spacecraft shield design requires early entry of radiation constraints into the design process to maximize performance and minimize costs. As a result, we have been investigating high-speed computational procedures to allow shield analysis from …

Finite Element Modal Formulation For Panel Flutter At Hypersonic Speeds And Elevated Temperatures, Guangfeng Cheng

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element time domain modal formulation for analyzing flutter behavior of aircraft surface panels in hypersonic airflow has been developed and presented for the first time. Von Karman large deflection plate theory is used for description of the structural nonlinearity and third order piston theory is employed to account for the aerodynamic nonlinearity. The thermal loadings of uniformly distributed temperature and temperature gradients across the panel thickness are incorporated into the finite element formulation. By applying the modal reduction technique, the number of governing equations of motion is reduced dramatically so that the computational time of direct numerical integration …

A New Method For Suboptimal Control Of A Class Of Nonlinear Systems, Ming Xin, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In this paper, a new nonlinear control synthesis technique (θ - D approximation) is presented. This approach achieves suboptimal solutions to nonlinear optimal control problems in the sense that it solves the Hamilton-Jacobi-Bellman (HJB) equation approximately by adding perturbations to the cost function. By manipulating the perturbation terms both semi-globally asymptotic stability and suboptimality properties can be obtained. The convergence and stability proofs are given. This method overcomes the large control for large initial states problem that occurs in some other Taylor expansion based methods. It does not need time-consuming online computations like the state dependent Riccati equation (SDRE) technique. …

A New Optimal Nonlinear Control Method And Its Application To Missile Guidance Law Design, Ming Xin, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In this paper, a new nonlinear control synthesis technique (q-D approximation) is discussed. By adding perturbations to the cost function this approach achieves a suboptimal solution to the Hamilton-Jacobi- Bellman (HJB) equation. By manipulating the perturbation terms both asymptotic stability and optimality properties are obtained. An application to the design of missile guidance law is presented and is compared with a similar technique (State Dependent Riccati Equation technique) used in problems of this class. © 2002 by the author(s).

State Dependent Riccati Equation Based Spacecraft Attitude Control, Ming Xin, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We present a new optimal control approach to the robust spacecraft attitude control in the framework of State Dependent Riccati Equation (SDRE) technique. To treat this highly nonlinear control system, we formulate it as a nonlinear optimal regulator problem. SDRE technique was well applied to this class of attitude control problem. We also synthesize a neural network based extra controller to achieve the robustness in the presence of the parameter uncertainties. A general spacecraft attitude regulation problem was studied to show the effectiveness of SDRE approach and robust extra control design. © 2002. Published by the American Institute of Aeronautics …

Accuracy And Efficiency In Fem Modeling Of Turbofan Acoustic Radiation, Eivind Listerud, Walter Eversman

Mechanical and Aerospace Engineering Faculty Research & Creative Works

It is shown that there is an increase in efficiency of acoustic radiation finite element modeling with the incorporation of cubic rather than quadratic serendipity elements. Cubic serendipity elements produce a given level of accuracy for acoustic pressure using a coarser mesh than required using quadratic elements, thus decreasing the CPU time needed for accurate modeling. These elements have been applied to the near field inlet and aft acoustic radiation models for a turbofan engine with the result of considerable reduction in the dimensionality of the problem without sacrificing accuracy. Visual observations of the gain in computational efficiency is supported …

Cfd Simulations Of Critical Components In Fuel Filling Systems, R. Banerjee, X. Bai, D. Pugh, Kakkattukuzhy M. Isaac, D. Klein, J. Edson, W. Breig, L. Oliver

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A comprehensive study is reported on the dynamics of critical components in the refueling process for passenger cars and light trucks. Nozzle, filler pipe, recirculation tube, tank, and canister are investigated. CFD simulations are conducted for flow rates of 4 liters/min (lpm) to 80 lpm for gasoline and up to 120 lpm for diesel fuel. Tank pressure, identified as a critical parameter controlling flow performance, is measured and utilized as a boundary condition. Flow simulation in a carbon canister, accomplished by treating the adsorbing carbon as a porous medium, indicates pressure drops which are in good agreement with published experimental …

Proper Orthogonal Decomposition Based Optimal Control Design Of Heat Equation With Discrete Actuators Using Neural Networks, Radhakant Padhi, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A new method is presented for the optimal control design of one-dimensional heat equation with the actuators being concentrated at discrete points in the spatial domain. This systematic methodology incorporates the advanced concept of proper orthogonal decomposition for the model reduction of distributed parameter systems. After deigning a set of problem-oriented basis functions an analogous optimal control problem in the lumped domain is formulated. The optimal control problem is then solved in the time domain, in a state feedback sense, following the philosophy of adaptive critic neural networks. The control solution is then mapped back to the spatial domain using …

A Quantitative Similarity Metric For Design-By-Analogy, Daniel A. Mcadams, Kristin L. Wood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

During the design and development of new products, design engineers use many techniques to generate and define new and "good" concepts. Inherent in this search for solutions is the conscious and unconscious reliance on prior experience and knowledge, or design-by-analogy. In this paper, a quantitative metric for design-by-analogy is developed. This metric is based on the functional similarity of products. By using this product-similarity metric, designers are able to formalize and quantify design-by-analogy techniques during concept and layout design. The methods, as developed in this paper, allow a designer with limited experience to develop sophisticated solutions that enhance the overall …

A Functional Basis For Engineering Design: Reconciling And Evolving Previous Efforts, Julie Hirtz, Robert B. Stone, Daniel A. Mcadams, Simon Szykman, Kristin L. Wood

Mechanical and Aerospace Engineering Faculty Research & Creative Works

In engineering design, all products and artifacts have some intended reason behind their existence: the product or artifact function. Functional modeling provides an abstract, yet direct, method for understanding and representing an overall product or artifact function. Functional modeling also strategically guides design activities such as problem decomposition, physical modeling, product architecting, concept generation, and team organization. A formal function representation is needed to support functional modeling, and a standardized set of function-related terminology leads to repeatable and meaningful results from such a representation. We refer to this representation as a functional basis; in this paper, we seek to reconcile …

Experimental Implementation Of Adaptive-Critic Based Infinite Time Optimal Neurocontrol For A Heat Diffusion System, Prashant Prabhat, S. N. Balakrishnan, Dwight C. Look

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Recently the synthesis methodology for the infinite time optimal neuro-controllers for PDE systems in the framework of adaptive-critic design has been developed. In this paper, first we model an experimental setup representing one dimensional heat diffusion problems. Then we synthesize and implement an adaptive-critic based neuro-controller for online temperature profile control of the experimental setup.

Proper Orthogonal Decomposition Based Feedback Optimal Control Synthesis Of Distributed Parameter Systems Using Neural Networks, Radhakant Padhi, S. N. Balakrishnan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A new method for optimal control design of distributed parameter systems is presented in this paper. The concept of proper orthogonal decomposition is used for the model reduction of distributed parameter systems to form a reduced order lumped parameter problem. The optimal control problem is then solved in the time domain, in a state feedback sense, following the philosophy of ''adaptive critic'' neural networks. The control solution is then mapped back to the spatial domain using the same basis functions. Numerical simulation results are presented for a linear and nonlinear one-dimensional heat equation problem in an infinite time regulator framework.

Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani

Chemistry Faculty Research & Creative Works

The interaction between two polymer layers, especially adhesion between them, plays an important role in polymer processing and other applications. Detailed knowledge of the molecular structure and dynamics of polymer interfaces, and how they relate to macroscopic mechanical properties, should help designers construct more functional systems. Unfortunately, there have been few studies where both molecular and macroscopic studies have been performed on similar systems. In previous studies from our group, we have probed the dynamics of poly(methyl acrylate) (PMA) and thermal behavior of poly(methyl methacrylate) (PMMA) on silica. These studies helped us paint a picture for strongly bound molecules on …

Forensic Investigation Of Failed Mast Arms Of Traffic Signal Supported Structures, Genda Chen, Michael G. Barker, D. Scott Mackenzie, Christopher W. Ramsay, Joe Alderson, Lokeswarappa R. Dharani, Jiaqing Yu

Civil, Architectural and Environmental Engineering Faculty Research & Creative Works

In Missouri, 11 traffic signal mast arms fractured at the arm-post weld connection in 7 years. To reduce this fatigue failure, the Missouri Department of Transportation developed a fatigue-resistant weld profile that increases the weld leg and reduces the slope of the weld at the toe. This study investigated causes of the failed arms, compared performance of new and old weld profiles, and suggested retrofitting measures for further investigation. The scope included a metallurgical investigation of one failed field mast arm, laboratory fatigue testing of five prototype mast arms (two new and three old profiles), and laboratory failure analysis of …

Adaptive Critic-Based Neural Network Controller For Uncertain Nonlinear Systems With Unknown Deadzones, Pingan He, Jagannathan Sarangapani, S. N. Balakrishnan

Electrical and Computer Engineering Faculty Research & Creative Works

A multilayer neural network (NN) controller in discrete-time is designed to deliver a desired tracking performance for a class of nonlinear systems with input deadzones. This multilayer NN controller has an adaptive critic NN architecture with two NNs for compensating the deadzone nonlinearity and a third NN for approximating the dynamics of the nonlinear system. A reinforcement learning scheme in discrete-time is proposed for the adaptive critic NN deadzone compensator, where the learning is performed based on a certain performance measure, which is supplied from a critic. The adaptive generating NN rejects the errors induced by the deadzone whereas a …