Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 77-79).
Drummond, Alastair Milne
The dynamic stability of a long, slender-bodied vehicle with a flexible fuselage is examined analytically in the supersonic speed regime. The small aspect ratio lifting surfaces are considered to be rigid but dependence of their angles of attack on fuselage flexibility is accounted for. The amplitude of pitching oscillation is restricted to ±10° about the zero-lift line by the nature of the unsteady, supersonic aerodynamic theory used. The stability problem is formulated by a set of non-linear differential equations with the non-linear contributions arising from both the inertia and the aerodynamic forces. The present analysis accounts for non-linear contributions up to third degree in the rigid body angle of attack. The stability of the short period mode is investigated using Routh-Hurwitz criteria and an expression representing a stiffness criterion for dynamic stability is obtained. The analytical development is so presented as to make it easily applicable to a supersonic, flexible vehicle with or without wings, e.g. a supersonic transport or a missile. Moreover to facilitate the evaluation of the effect of flexibility and non-linearities on dynamic stability, four cases are considered separately: a. Rigid body equations of motion, without non-linear terms b. Rigid body equations of motion, with non-linear terms c. Flexible body equations of motion, without non-linear terms d. Flexible body equations of motion, with non-linear terms. A numerical example is presented towards the end which investigates the dynamic stability of a flexible, supersonic transport configuration. The conclusions from the example are: 1. The non-linearities can be safely neglected for rigid aircraft, but not for wingless vehicles. 2. Flexibility affects the stability through the lift and pitching moment and also by introducing two more possible equilibrium points. 3. The amount of work involved in finding a solution is markedly increased by the necessity of solution of more characteristic equations of higher degree. 4. The stiffness criterion can be used to adjust the stiffness distribution to one that can make an unstable configuration stable. The usefulness of the method is two-fold. For a flexible vehicle with known geometric, mass and elastic properties, the method can predict its dynamic stability. This feature is of considerable importance particularly in the design stage. On the other hand, if an aircraft with known geometry, total mass and centre-of-gravity location proves to be dynamically unstable, then the analysis provides a stiffness criterion by which it can be made stable. The analysis involves a considerable amount of computation and hence seems to be particularly suited for solution by a digital computer. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate
Christensen, Gustav Strom
This thesis treats system stabilty from three separate points of view. 1. State Space Analysis 2. Complex Frequency Plane Analysis 3. Time Domain Analysis Asymptotic stability is considered in state space. Using state space and the gradient method an expression is derived for the total time derivative of the Liapunov function. This expression is a special case of the general Zubov equation, however, it does not lend itself to an explicit, exact solution except in special cases. Global asymptotic stability and bounded input -bounded output stability is considered in the complex frequency plane. Here a method developed by Sandberg has been applied to some systems the linear part of which has poles on the imaginary axis. The solution of an example of this type via the Sandberg method and the Popov method shows that the two methods give essentially the same result for the example considered. Bounded input - bounded output stability is considered in the time domain using two separate methods. One, a method developed by Barrett using Volterra series has been extended to cover cases with a nonlinearity of 2nd and 4th degree. Two, a method depending on the contraction mapping principle is developed and applied to several types of systems. It is shown that this method generates the Volterra series found by Barrett's method, and thus we can actually determine a region where, the solution of a given differential equation can be represented in the form of a Volterra series. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate
Wimalsiri, Walallawita K.
No description available.
United States military presence in Central Asia implications of United States basing for Central Asian stabilityDockery, Leon W. 06 1900 (has links)
This thesis examines the United States policy for establishing overseas military bases particularly in Central Asia. The major transformational trends in improving United States military capabilities over the past two decades, and the changing international security environment, have shaped the way American leaders focus on their global military posture strategy. Immediately following the September 11, 2001 terrorist attack, the United States moved quickly to establish a presence in Uzbekistan and Kyrgyzstan, and after the defeat of the Taliban, several bases became available in Afghanistan. Soviet military influence in Central Asia will be examined and compared to current United States policies and procedures. While military bases still maintain several strategic advantages in terms of response times and maneuver, there needs to be an equally sized effort to explore how these bases can provide stability. Achieving stability in Central Asia will require the United States to move away from the conventional ideology of basing, which it has used for many years, and to embrace policies and procedures that can meet the military mission and gain the trust of the host country. / US Air Force (USAF) author.
Taylor, Peter James
vi, 92 leaves : appendices / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Applied Mathematics, University of Adelaide, 1971
There are several technical challenges in large scale heavy oil processing. In the oil sand industry, for example, the existence of water-in-oil emulsion in diluted bitumen produced from froth treatment presents a great challenge to the industry. In this work, the effect of different bitumen components, including asphaltenes, maltenes (deasphalted bitumen) and indigenous naphthenic acids (NAs), on the stability of water-in-diluted model oil emulsion was systematically investigated. A biodegradable polymer was developed and introduced to break the water-in-oil emulsions. The stability of water-in-oil emulsions depends on the mechanical barrier between two approaching water droplets in model oil with bitumen components. The micron-scale techniques are used in this study to study the mechanical behavior of emulsion drops due to its priority to maintain the surface area to volume ratio which is representative of the commercially observed emulsions. Several parameters, including interfacial tension isotherm, crumpling ratio and probability of coalescence, were measured to understand the interfacial reheology. Based on these experiments, the mechanical properties of emulsion drops can be evaluated in situ. A non-toxic and biodegradable polymer, ethylcellulose, was used to break up the water-in-diluted bitumen emulsion. The demulsification mechanism was studied in this work. The knowledge from this work provides improved insights on molecular mechanism of emulsion stability/demulsification and contributes to the design of demulsification systems in industrial oil sands extraction processes. / Chemical Engineering
11 September 2006
The objective of this thesis is to maintain the stable operation of an industrial cogeneration system after transient disturbance caused by external utility system. Both dynamic stability and the transient stability of the power system are investigated. The dynamic stability analysis is to derive the stable frequency of the power system without causing the system frequency oscillation with the small amount of load change. On the other hand, the transient stability analysis will simulate the system response during system fault contingency to determine the system capability to restore the stable operation. Based on the transient stability analysis, the protection relay setting for both tie line tripping and load shedding are derived. In order to confer the influence of the system stability with the industrial cogeneration system, we use the practical cogeneration system of China Steel Corporation (CSC) to analyze the transient stability of the whole system and dynamic stability of 700B/800B subsystem. Executing the load flow analysis of the CSC cogeneration system is solved by CYMSTAB software to derive the system prefault operating data. The system transient parameters are used to construct the system model. The system transient stability analysis is executed to solve the strategies of tie line tripping and the amount of load shedding to restore the system stability after fault contingency. Finally, the external fault at Fong-Nong substation in Tai-power is used to simulate and analyze the transient stability of CSC cogeneration system. Besides, the dynamic model of 700B/800B subsystem of the CSC cogeneration and selected adaptive control parameters are applied to simulate the dynamic response of system islanding operation.
Moore, Robert Lee,
Thesis (Ph. D.)--Ohio State University, 1978. / Includes vita. Includes bibliographical references (leaves 175-177). Available online via OhioLINK's ETD Center.
Improving the Educational Outcomes for Minorities: A Study of the Interactive Effects of Personnel Stability and Representative BureacracyMorton, Tabitha Susan 16 December 2013 (has links)
The goal of this dissertation is to determine how to create more equal public policy outcomes within the realm of public education. It is a well known fact that despite the passage of legal decisions such as Brown (1954) and federal policies like No Child Left Behind (2001), Latino and African American students still perform at lower rates than Anglo students. This poor academic performance results in lower graduation rates, lower college attendance, and a lower socioeconomic status than Anglos. This dissertation therefore sought to determine if two common bureaucratic theories, representative bureaucracy and personnel stability, could be used in combination with one another in order to improve the educational policy outcomes for African American and Latino students. Using data from Texas school districts from 1994-2010 and a cross-sectional longitudinal research design, I find that while each theory on its own improved the outcomes for these groups, the two did not have a significant combined effect on every indicator. Instead I find evidence of a substitution effect which allows one strategy to be used in place of the other in order to improve the academic performance of minority students. This creates a unique situation as this analysis suggests that there are other bureaucratic factors working to prevent an interactive effect from occurring on a consistent basis. Thus the next steps are to apply the same theories to other public organizations in order to determine if my findings are unique to public education and to determine if other public administration theories can be used to improve the outcomes for African American and Latino students.
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