Digital Commons Network^™

Hydrodynamic Wave Contributions To Combustion Instability In Rockets, Esam M. T. Abu-Irshaid

Doctoral Dissertations

Experimental measurements suggest that a new source of instability in rocket motors is due to hydrodynamic disturbances. These disturbances, if ignored, could impact our assessment of rocket motor performance. In this work, the corresponding problem of hydrodynamic instability is considered. A mathematical model for these disturbances is carried out by perturbing the continuity and momentum equations. A one dimensional model which represents the wave disturbances in time and space is implemented to quantify the amplification rate, in time or space, and the wave amplitude. The only available measurements of these disturbances arise in cold flow experiments that simulate the gas …

The Thermophysical Roll Of Nanoparticles In Nanofluidic Heat And Mass Transport, Chan Hee Chon

Doctoral Dissertations

Nanofluids are colloids that consist of a base fluid and nanometer sized metallic particles, which serve to improve the heat and mass transport characteristics of nanofluids over those of the base fluid. Many researchers, attracted to the highly enhanced thermal conductivity, have studied nanofluids, and yet have never been able to reveal the basic mechanisms of their characteristic improvements. This present work thus seeks to gain an understanding of the role of nanoparticles in nanofluidic heat and mass transport characteristics through three experimental measurements: 1) thermal conductivity measurement, 2) thermophoretic motion measurement, and 3) evaporation measurement.

Using thermal conductivity, thermophoresis, …

The Stability Analysis Of Linear Dynamical Systems With Time-Delays, Ajeet Ganesh Kamath

Doctoral Dissertations

Time-delay systems, which are also sometimes known as hereditary systems or systems with memory, aftereffects or time-lag, represent a class of infinite-dimensional systems, and are used to describe, among other types of systems, propagation and transport phenomena, population dynamics, economic systems, communication net- works and neural network models. A key method for the stability analysis of time- delay dynamical systems is the Lyapunov’s second method, applied to functional differential equations. Specifically, stability of a given linear time-delay dynamical system is typically shown using a Lyapunov-Krasovskii functional, which involves a quadratic part and an integral part. The quadratic part is usually …

Analysis And Control Of Nonnegative Systems, Jayanthy Ramakrishnan

Doctoral Dissertations

Nonnegative systems are dynamical systems with nonnegative states for random non- negative initial conditions. A subclass of nonnegative systems are compartmental systems characterized by conservation laws.Nonnegative and compartmental systems have widespread applications in biological systems, medical systems, thermodynamic systems, network systems, economic systems, etc.

In this dissertation we have investigated the applications of nonnegative systems in biological and network systems. The specific focus in biological systems has been in the area of pharmacokinetics and we have addressed the consensus problem in network systems. We have specifically focused on the time-delay present in compartmental systems and have investigated the behavior of …

A Theory For Modified Conservation Principles Optimization Of Cfd Algorithm Fidelity, Sunil Sahu

Doctoral Dissertations

A theory is developed in one and two space dimensions that successfully predicts optimal algorithm constructions for the convection operator intrinsic to unsteady Navier- Stokes (NS) problem statements. The analysis statement is parameterized via a Taylor series (TS) modification to the parent NS conservation principles statements. Phase velocity and amplification factor error analyses are enabled via weak form discretized implementations assembled at the generic node. The parameterized error statement is then resolved into a Taylor series expansion in non-dimensional wave number space, admitting identifications that progressively annihilate lowest order error terms. The theory computational implementation is via a Galerkin weak …

Development Of A Potentially Accurate And Efficient Les Cfd Algorithm To Predict Heat And Mass Transport In Inhabited Spaces, Marcel Andre Grubert

Doctoral Dissertations

During the last decades many advances have been made in the prediction of turbulent flow behavior, due largely to new achievements in the field of computational fluid dynamics (CFD). For many years the Reynolds-averaged Navier-Stokes (RaNS) approach, which employs time-averaging, has been the work-horse of the industry in predicting turbulent flow in real-world applications. Although the accuracy of those turbulent flows and the details in flow structure are mostly limited due to its empirical modeling approach, the RaNS based algorithms are able to achieve solutions in relative short amounts of computational time using relatively coarse meshes.

But with increased computational …

High Performance Control Of A Transmission Based Servo Actuator System, Renbin Zhou

Doctoral Dissertations

High performance actuation is a key factor in the industrial robot area. The transmission based servo actuator system (TBA) is a new type of robot actuator with a brushless DC servo motor and a three speed discrete variable transmission (DVT). The proposed TBA design can match the performance of a typical hydraulic actuator with compact size and weight.

The TBA is a typical hybrid dynamic system consisting of three continuous dynamic systems and a discrete state controller. This dissertation addresses the fundamental problems associated with the TBA system control from a hybrid system point of view.

A detailed dynamic model …