Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on March 2, 2010. Major professor: Xi Wu, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Mechanical Engineering." "June 2009." Includes bibliographical references (p. 90-91).

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Bruce C. Denardo, Thomas J. Hofler. Includes bibliographical references (p. 81). Also available online.

published_or_final_version / abstract / toc / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil and Structural Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

In this thesis we explore the relationship between aeroelastic flutter and multiparameter spectral theory. We first introduce the basic concept of the relationship between these two fields in abstract terms. Then we expand on this initial concept, using it to devise visualisation methods and a wide variety of solvers for flutter problems. We assess these solvers, applying them to real-life aeroelastic systems and measuring their performance. We then discuss and devise methods for improving these solvers. All our conclusions are supported by a variety of evidence from numerical experiments. Finally, we assess all of our methods, providing recommendations as to their use and future development. We do achieve several things in this thesis which have not been achieved before. Firstly, we solved a non-trivial flutter problem with a direct solver. The only direct solvers that have previously been presented are those that arise from classical flutter analysis, which applies only to very simple systems. Secondly, and as an extension of this first point, we solved a system with Theodorsen aerodynamics (approximated by a highly accurately) with a direct solver. This was achieved in an industrially competitive time (0.2s). This has never before been achieved. Thirdly, we solved an unstructured multiparameter eigenvalue problem. Unstructured problems have not been considered before, even in theoretical literature. This result is thus of significance both for multiparameter spectral theory and aeroelasticity. However, the single most important contribution of this thesis is the opening of a whole new field of study which stretches beyond aeroelasticity and into other industries: the treatment of instability problems using multiparameter methods. This field of research is wide and untrodden, and has the potential to change the way we analyse instability across many industries.

Internal friction has been known to be a cause of whirl instability in built-up rotors since the early 1900's. This internal damping tends to make the rotor whirl at shaft speeds greater than a critical speed, the whirl speed usually being equal to the critical speed. Over the years of research, though models have been developed to explain instabilities due to internal friction, its complex and unpredictable nature has made it extremely difficult to come up with a set of equations or rules that can be used to predict instabilities accurate enough for design. This thesis deals with suggesting improved methods for predicting the effects of shrink fits on threshold speeds of instability. A supporting objective is to quantify the internal friction in the system by measurements. Experimental methods of determining the internal damping with non-rotating tests are investigated, and the results are correlated with appropriate mathematical models for the system. Rotating experiments were carried out and suggest that subsynchronous vibration in rotating machinery can have numerous sources or causes. Also, subsynchronous whirl due to internal friction is not a highly repeatable phenomenon.

This thesis investigates the development of an automated fault detection system developed for a novel lightweight railway material haulage system; in particular, the study aims to detect railway track faults at the incipient stage to determine the feasibility of maintenance decision support, ultimately with the function of preventing catastrophic failure. The proposed approach is an extension of the current state of the art in fault detection of unsteady machinery. The most common railway track faults associated with train derailment were considered; namely, horizontal and transverse crack propagation, mechanical looseness, and railbed washout were the faults of interest. A series of field experiments were conducted to build a database of vibration, speed, and localization data in healthy and faulted states. These data were used to develop, investigate, and validate the effectiveness of various approaches for fault detection. A variety of feature sets and classification approaches were investigated to determine the best overall configuration for the fault detector. The feature sets were used to condense data segments and extract characteristics that were sensitive to damage, but insensitive to healthy variations due to unsteady operation. The pattern recognition classifiers were used to categorize new data members as belonging to the healthy class or faulted class. The fault detection results from the proposed approach were promising. The feasibility of an automated online fault detection system for the lightweight material haulage system examined in this study was confirmed. The conclusions of this research outline the major potential for an iv effective fault detection system and address future work for the practical implementation of this system.

The cross-flow past a pair of equal-diameter circular cylinders, arranged in a staggered configuration, was investigated experimentally in a closed-circuit water tunnel at Reynolds numbers, based on the mean-flow velocity and the cylinder diameter, within the lower subcritical range. The wake formation process was studied employing dye-injection flow visualization and hot-film measurements. The main emphasis was placed on acquiring a physical understanding of the mechanisms leading to vortex shedding, and particularly on the effect of a forced oscillation transverse to the flow direction of either of the two cylinders. For comparison purposes, investigations were also carried out with both cylinders stationary. / Experimental results showed that, for a reasonably large angle of incidence, the flow in the wake of a stationary cylinder pair could be characterized by two distinct periodicities, each of which was dominant on one side of the wake. Furthermore, for lower Reynolds numbers (Re < 1.0x10 4), there was an integral relationship between the two Strouhal numbers, but this integral relationship was no longer maintained for Re > 1.0x10 4. On the other hand, the flow around stationary cylinders for a small angle of incidence was characterized by a single Strouhal number, which remained approximately constant over the entire Reynolds number range. / For all the cylinder configurations investigated the wake flow patterns remained essentially the same as those of the corresponding static cases, when either of the two cylinders was forced to oscillate with a nondimensional forcing frequency less than approximately 0.10. However, beyond this value, the wake underwent considerable modification vis-a-vis when the cylinders were stationary, and the flow pattern within the wake was strongly dependent on the value of the forcing frequency. In particular, there were distinct regions of synchronization between the dominant wake periodicities and the cylinder oscillation; these synchronization regions involved sub- and superharmonics as well as fundamental synchronizations. With either upstream or downstream cylinder oscillation, the wake on the mean-flow side of the downstream cylinder synchronized with the shear layers separated from its outer surface, whereas synchronizations on the mean-flow side of the upstream cylinder were caused by the periodicities formed from the interaction of the other three shear layers. / The flow phenomena associated with the synchronizations were described in detail via flow visualization. The organization of the wake was strongly dependent on whether it was the upstream or downstream cylinder which was oscillating. The synchronized wake on the mean-flow side of the downstream cylinder at both lower and higher oscillation frequencies for upstream cylinder oscillation was observed to form either by the shedding of independent vortices or by the coalescence of two or more vortices. However, for downstream cylinder oscillation, although the synchronizations on this side of the wake at lower oscillation frequencies were caused by the shedding of independent vortices or by the coalescence of vortices, those at higher oscillation frequencies were the consequence of the coalescence of vortices only. For large incidence angles, the number of shear layers separated from the downstream cylinder which interacted with those separated from the upstream cylinder was critical in causing the synchronizations on the mean-flow side of the upstream cylinder. / In most cases, the flow for all the cylinder configurations traversed between the same patterns as those obtained when the cylinders were placed stationary at their minimum and maximum transverse spacings; but there were also some situations where the oscillation of either cylinder pushed the flow outside the regimes associated with the stationary configurations. The synchronization ranges obtained when the upstream or downstream cylinder was oscillating were different from each other, and these ranges were much wider than the corresponding synchronization ranges for a single oscillating cylinder. For two cylinders, an analysis of the fundamental synchronization showed that the frequency range over which this occurred was much broader for upstream cylinder oscillation than for downstream cylinder oscillation. Also, the fundamental synchronization ranges for downstream cylinder oscillation were closer to those for single cylinder oscillation in comparison to those for upstream cylinder oscillation.

Talking about ultrasonic vibration we can say that it is the essential thing of experimental physics science. The ultrasound is applied amply, for example in: medicine and pharmacy, dimensional and diagnostics devise, mechatronic, mine working, building, automobile and aliment industry, textile industry, connection, energetic – that is not all the actions ranges off people doing, where he is applying. Although hypersonic technologic rise and begin proceed lately, however they are taking the strongest positions in science and technique. Ultrasonic vibration systems (UVS), are designed for push realization, the main function is - interaction with other solid at the dot and to establish the secret elliptical movement trajectory. Also we need a control of this movement, stabilized cooperating with other solids and to keep particular dynamic parameters. Destination of the work: To establish mathematical model of ultrasonic vibration systems (UVS) and to explorer his work dot characterizations. Tasks: 1. Classification, material analysis of existing elliptical movement formative ultrasonic vibration systems (UVS), construction internal, resilient wave spread forms, vibration stimulation tempers. 2. To examine made-up system by finite essential method : determine her vibration parameters – her forms and frequencies; to take measurements of dots, witch formative elliptical trajectory vibration displacement and to establish their movement trajectory. 3. To compare by analytical... [to full text]