Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves[126]-128).

Thesis (Aeronautical and Astronautical Engineer Degree and M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2002. / Thesis advisor(s): Brij Agrawal, Hong-Jen Chen. Includes bibliographical references (p. 85-88). Also available online.

Experience shows that the noise and sound quality in vehicles are often a recurring criticism. The bodies of modern vehicles consist predominantly of thin sheets of metal. It is hard to prevent the excitation of bending vibrations and the subsequent emission of disturbing noise while driving. The noise spectrum in a car that can be heard by the driver is from ”latent roar” to ”chattering” noise of the body and engine. In automotive vehicles damped materials, especially plastics or materials made from sheet metal and surface damping treatments, are used. Those have high internal energy losses and damp sound oscillatory systems found in the body or interior of cars. A further advantage of such treated components is that they are applied to existing components working over wide temperature and frequency ranges. Many companies provide such ”sound-absorbing compounds”. The requirements for these damping materials are high temperature-resistance, water repellence, fuel and oil-resistance and good adhesion to the base material [17]. The acoustic properties, especially the damping of the plate vibrations through rubber are of interest. the question arises how can the damping coeficient of coated metal sheets can be measured and secondly, by how much the road noise is reduced when built-in sheets are coated with a known damped material. With the Oberst Bar Test Method (named after Dr. H. Oberst) the properties are determined of the internal damping materials that can be used to simulate mechanical constructions to determine damping of larger surfaces. This method describes a laboratory test procedure for measuring the mechanical properties of damped materials. A block diagram of the test system consisting of a damped material bonded to a vibrating cantilever steel bar is shown in figure 2.1. This method is useful for testing materials such as metals, enamels, ceramics, rubbers, plastics, reinforced epoxy matrices and wood. In addition to damping measurement, the test allows for the determination of the Young’s modulus E of the material. E is calculated from the resonance frequency of a given mode and from the physical constants of the bar. By associating the damping factor with the Young’s modulus, a complex quantity is defined which is called the Complex Modulus of Elasticity. Measurements of dynamic mechanical properties are also useful in the research on the molecular structure of materials.

In the last two decades, the emphasis in aircraft maintenance has been on developing online structural health monitoring systems to replace conventional non destructive inspection techniques which require considerable down-time, human effort and cost. Vibration based damage detection is one of the most promising techniques for implementation in Structural Health Monitoring (SHM). In vibration based methods, the presence of damage is detected by monitoring changes in one of the dynamic parameters of the structure, resonant frequencies, modeshapes or damping characteristics. Compared to modeshape based methods, frequency based methods have the advantage that measurements need to be taken only at a single location. Previous developments on frequency based techniques have relied on Finite Element Model updating; analytical techniques have hitherto been restricted to beams due to the complexity in developing equations for cracked two dimensional structures. In this thesis the analytical approach using an energy formulation is extended to plates with through-thickness cracks, where modeshapes from either numerical modelling or experimental measurements can be employed to determine the energy of vibration. It is demonstrated that by using a hybrid approach, incorporating experimentally measured modeshapes along with measured changes in frequencies, the damage parameters can be estimated without resorting to theoretical modelling or numerical analysis. The inverse problem of finding the crack location, size and orientation from measured changes in frequencies is addressed using minimisation techniques. The forward problem and the inverse algorithm is first validated using numerical simulation and experimental testing of beams with edge cracks and centre cracks. The application of the methodology to the two dimensional case is then validated by numerical simulation and experimental modal analysis of plates with through thickness cracks. A statistical procedure is developed for determination of the 90/95 probability of crack detection and the minimum detectable crack size in both cases. It is demonstrated that the measurement of frequency changes can be successfully employed to detect and assess the location and size of cracks in beams and plates, using modeshapes from theory, Finite Element Analysis.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Vita. / Includes bibliographical references. / by John Shaw. / Ph.D.

No description available.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 92-93). / x, 93 leaves, bound ill. 29 cm

Thesis (Ph. D.)--Duke University, 2008. / Includes bibliographical references.

This thesis covers the investigation of active damping on a cruciform beam laboratory structure along with the development of this structure. Also important to this and other research was the development of a calibration apparatus that produces accurate, repeatable calibrations for several types of laboratory instruments. The cruciform beam model is developed out of a simpler beam-cable model with the addition of a crosspiece that produces a pair of closely-spaced modes. This model is developed theoretically and verified experimentally. Experimental verification is also obtained for theoretical results in the simultaneous design of a structure and control system. A spatial filtering method for determining the modal response of the structure from the physical response is also investigated. / M.S.

The dissertation investigates helicopter trim and stability during level bank-angle and diving bank-angle turns. The level turn is moderate in that sufficient power is available to maintain level maneuver, and the diving turn is severe where the power deficit is overcome by the kinetic energy of descent. The investigation basically represents design conditions where the peak loading goes well beyond the steady thrust limit and the rotor experiences appreciable stall. The major objectives are: 1) to assess the sensitivity of the trim and stability predictions to the approximations in modeling stall, 2) to correlate the trim predictions with the UH-60A flight test data, and 3) to demonstrate the feasibility of routinely using the exact fast-Floquet periodic eigenvector method for mode identification in the stability analysis. The UH-60A modeling and analysis are performed using the comprehensive code RCAS (Army's Rotorcraft Comprehensive Analysis System). The trim and damping predictions are based on quasisteady stall, ONERA-Edlin vi (Equations Differentielles Lineaires) and Leishman-Beddoes dynamic stall models. From the correlation with the test data, the strengths and weaknesses of the trim predictions are presented. / by Ranjith Mohah. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.