Browsing by Author "Dr. James Selgrade, Committee Member"

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The Aerodynamic Analysis and Aeroelastic Tailoring of a Forward-Swept Wing
(2006-05-08) Roberts, David William; Dr. Kara Peters, Committee Member; Dr. Charles E. Hall, Committee Chair; Dr. James Selgrade, Committee Member
The use of forward-swept wings has aerodynamic benefits at high angles of attack and in supersonic regimes. These consist of reduction in wave drag, profile drag, and increased high angle of attack handling qualities. These increased benefits are often offset due to an increase in structural components, to overcome flutter and wing tip divergence due to high loading of the wing tips at high angles of attack. The use of composite materials and aeroelastic tailoring of the structures eliminates these instabilities without a significant increase in weight. This work presents the design of an aeroelastic wing structure for a highly forward-swept wing, and the verification of the aerodynamic and structural finite element analysis through experimental testing.
Analysis and Parameter Estimation of the Aerodynamic and Handling Qualities of the C-130A Modified With Wing Tip Tanks
(2004-12-02) Phillips, David; Dr. Charles E. Hall Jr., Committee Chair; Dr. Ashok Gopalarathnam, Committee Member; Dr. James Selgrade, Committee Member
This work presents the background, flight testing, and resulting change in the aerodynamic and handling qualities of a C-130A Hercules modified with wing tip tanks. The data collected during the baseline and modified flight tests of this aircraft demonstrated the potential aerodynamic benefits of a tip tank design that incorporates a greater aspect ratio and end plating effects. Wing mounted pressure belts measured a 24% increase in local Cl near the tip tanks. This local increase in lift contributed to a 38% increase in CL max for the airplane. The pressure and dynamic data was gathered using a LIFT (Linux In Flight Testing) system, and it laid the foundation for finding the longitudinal and lateral directional stability coefficients of the airplane. Then using MATLAB® and the System IDentification Programs for AirCraft (SIDPAC) to reduce this data, it was possible to generate aerodynamic, lateral, and longitudinal parameters that clearly proved the overall benefits of the design change. The demonstrated lift benefits of these uniquely designed tip tanks for the C-130A cargo transport proved that by capitalizing on the benefits of a combination tip tank and end plate design it is possible to generate increased lift without adversely affecting the stability and dynamic parameters of the aircraft.
Deployment Dynamic of Space Tether Systems
(2007-08-08) Mantri, Parag; Dr. James Selgrade, Committee Member; Dr. Larry Silverberg, Committee Member; Dr. Greg Buckner, Committee Member; Dr. Andre Mazzoleni, Committee Chair
The Design, Analysis, Construction and Testing of an Uninhabited Aero Vehicle Platform
(2003-12-31) Burgun, Robert Scott; Dr. James Selgrade, Committee Member; Dr. Eric Klang, Committee Member; Dr. Charles E. Hall Jr, Committee Chair
An uninhabited aero vehicle platform design is presented. This encompasses the landing gear system and the structures of the vehicle. The landing gear system consisted of the design, construction and testing of the main and nose gears. The testing of the landing gear resulted in a valid system that could then be integrated into the vehicle. The vehicle structures are composed of various configurations of composite sandwiches. Extensive material testing was conducted to experimentally produce the physical properties of the materials. These properties and techniques can be utilized by other vehicle designs. The structural design was refined and ultimately verified within a finite element analysis program, ANSYS. This analysis implemented a composite shell element that utilized all of the material properties gained from the material testing. This work resulted in an analyzed and constructed vehicle. Ultimately the vehicle was load tested to verify the analytical results.
On the Periodic Nature of Solutions to the Reciprocal Difference Equation with Maximum
(2005-04-05) Bidwell, John Charles; Dr. John E. Franke, Committee Chair; Dr. Stephen Schecter, Committee Member; Dr. Xiao B. Lin, Committee Member; Dr. James Selgrade, Committee Member
We prove that every positive solution of the difference equation x[subscript n] = max[A[subscript i] ⁄ x[subscript n-i] | i ∈ [1,k]] is eventually periodic, and that the prime period is bounded for all positive initial points. A lower bound, growing faster than polynomially, on the maximum prime period for a system of size k is given, based on a model designed to generate long periods. Conditions for systems to have unbounded preperiods are given. All cases of nonpositive systems, with either the A values and/or initial x values allowed to be negative, are analyzed. For all cases conditions are given for solutions to exist, for the solution to be bounded, and for it to be eventually periodic. Finally, we examine several other difference systems, to see if the methods developed in this paper can be applied to them.
On the Solvability of Nonlinear Discrete Multipoint Boundary Value Problems
(2007-04-17) Taylor, Padraic Whittingham; Dr. Jesus Rodriguez, Committee Chair; Dr. James Selgrade, Committee Member; Dr. Tom Lada, Committee Member; Dr. Kailash Misra, Committee Member
In this manuscript we study nonlinear, discrete, multipoint boundary value problems. We investigate two types of problems. We first consider scalar, nonlinear, multipoint boundary value problems. We provide sufficient conditions for the existence of solutions. By allowing more general boundary conditions and by imposing less restrictions on the nonlinearities, we obtain results that extend previous work in the area of discrete boundary value problems. [8,9]. We also study weakly nonlinear, discrete systems. We provide sufficient conditions for the existence of solutions and we present a qualitative analysis of the way the solutions depend on the parameter.
Physiologically Based Model Development and Parameter Estimation: Benzene Dosimetry in Humans and Respiratory Irritation Response in Rodents
(2005-07-11) Yokley, Karen Alyse; Dr. Hien Tran, Committee Chair; Dr. Mette Olufsen, Committee Member; Dr. Paul Schlosser, Committee Member; Dr. James Selgrade, Committee Member
One can form mathematical equations based on a combination of chemistry, physics, and biological information to represent a physiological system. Once a model is formulated based on the physiological system, we must make sure that the inputs or parameters to the model also faithfully represent the system. In this study, we adapt and combine existing mathematical models to describe different physiological systems. Benzene is myelotoxic and causes leukemia in humans when they are exposed to high doses by inhalation (<1 ppm) for extended periods; however, leukemia risks in humans at lower exposures are uncertain. Benzene occurs widely in the work environment and in outdoor air, although mostly at concentrations below 1 ppm. Hence, we recognize the importance of assessing the risk to humans when they are exposed to benzene at low concentrations. In Chapter 2, we describe a physiologically based pharmacokinetic (PBPK) model for the uptake and elimination of benzene in humans to relate the concentration of inhaled benzene to the tissue doses of benzene and its key metabolites, benzene oxide, phenol, and hydroquinone. To account for variability among humans, the mathematical model must be integrated into a statistical framework that acknowledges sources of variation in the data due to inherent intra- and inter-individual variation, measurement error, and other data collection issues. The main contribution of Chapter 2 is the estimation of population distributions of key PBPK model parameters. In particular, a Markov Chain Monte Carlo (MCMC) technique is employed to fit the mathematical model to two data sets, thereby updating the estimated parameter distributions. We first considered only variability in metabolic parameters, as observed in previous in vitro studies, but found that it was not sufficient to explain observed variability in benzene pharmacokinetics. Variability in physiological parameters, such as organ weights, must also be included to faithfully predict the observed human population variability. Inhaled gases can also cause respiratory depression by irritating (stimulating) nerves in the nasal cavity. In order to better understand how the nervous system responds to such chemicals, we have created a model to describe how the presence of irritants affects respiration in the rat. By combining and adapting two previous models, one that evaluates the relationship between inhaled acrylic acid vapor concentration and the tissue concentration in various regions of the nasal cavity and another model which describes the baroreflex-feedback mechanism regulating human blood pressure, we created a system of equations that models the sensory irritant response in rats. The adapted model in Chapter 3 focuses on the dosimetry of these reactive gases in the respiratory tract, with particular focus on the physiology of the upper respiratory tract, and on the neurological control of respiration rate due to signaling from the irritant-responsive nerves in the nasal cavity. Further, the model is evaluated and improved through optimization of particular parameters to describe formaldehyde-induced respiratory response data and through sensitivity analysis. The model in Chapter 3 describes this formaldehyde data well and is expected to translate well to other irritants.