Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

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Thesis (M.S.)--Rochester Institute of Technology, 1994. / Typescript. Bibliography: leaf 59.

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International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Today’s telemetry specifications are requiring electronic systems to not only survive, but operate through severe dynamic environments. Pyrotechnic shock and Random Vibration are among these environments and have proven to be a challenge for systems that rely on highly stable, low phase noise signal sources. This paper will mathematically analyze how Pyrotechnic shock and Random Vibration events deteriorate the phase noise of crystal oscillators (XO).

This dissertation is concerned with the responses of nonlinear systems to both deterministic and stochastic excitations. For a single-degree-of-freedom system, the response of a simply-supported buckled beam to parametric excitations is investigated. Two types of excitations are examined: deterministic and random. For the nonlinear response to a harmonic axial load, the method of multiple scales is used to determine to second order the amplitude-and phase-modulation equations. Floquet theory is used to analyze the stability of periodic responses. The perturbation results are verified by integrating the governing equation using both digital and analog computers. For small excitation amplitudes, the analytical results are in good agreement with the numerical solutions. The large-amplitude responses are investigated by using simulations on a digital computer and are compared with results obtained using an analog computer. For the stochastic response to a wide-band random excitation, the Gaussian and non-Gaussian closure schemes are used to determine the response statistics. The results are compared with those obtained from real-time analysis (analog-computer simulation). The normality assumption is examined. A comparison between the responses to deterministic and random excitations is presented. / Ph. D.

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As the industry is being reshaped concentrically around sustainability, the consumption of fossil fuels is targeted to decrease day by day. As a consequence of that, a righteous rise of electricity as energy source prevails in different branches of industry. It results for electric vehicle components to increase in size and weight which in fact were relatively smaller on conventional fossil fuel driven vehicles e.g. trucks. Every component weighing more than two kilograms is classified as a large component by Scania and these large electric components uncovers the need of evaluation of established testing methods in terms of their validity. This thesis project was carried out at Scania, Södertälje, and deals with the investigation on vibration testing methods that are currently used in different fields of engineering and identification of potentially applicable ones at Scania in testing large components. A case study on the stiffness of an individual component is performed to assess its impact on alteration of eigenfrequencies. Few case studies based on empirical tests as well as finite element method simulations on certain large components, i.e. high voltage junction box and battery packs, are performed with respect to their vibration behaviours while undergoing Scania’s established vibration testing spectra. Investigation into the vibration behaviour on dependence on measurement locations were performed. Additionally, rudimentary case studies are conducted on thermal loads during vibration testing, thermal dwell time, and required energy to oscillate large components at certain levels. How thermal features of the component are affected due to its size is noted. / Den senaste tekniska paradigmen inom fordonsindustrin är fokus på minskning av beroende på fossila bränslen, högre energisnålhet och en ökad hållbarhet och effektivitet i produktionsprocessens alla delar. Detta och de stora genombrotten i batteritekniken hade som påföljd att utvecklingen av fordon riktades mot elektrifiering av alla fordon. Elmotorer har sedan tidigare funnit sin tillämpning på mindre maskiner i inomhusmiljöer som t.ex. palldragare och lasttruckar. För tyngre applikationer som t.ex. personbilar och lastbilar ställs det helt nya krav på komponenternas storlek och prestanda, vilket leder till de elektriska komponenternas högre vikt. Scania, som vill vara ledande inom denna omställning, klassificerar alla komponenter med större vikt än 2 kg som stora komponenter. De stora elektriska komponenterna skapar ett behov att utvärdera de aktuella testmetoderna och verifiera deras validitet. Det här magisterexamensarbetet har genomförts på Scania i Södertälje och handlar om undersökning av vibrationstestningsmetoderna som nuförtiden används i olika teknikområden samt identifiering av de eventuellt applicerbara metoderna för provning av stora elektriska komponenter. En fallstudie genomfördes gällande en individuell komponent och påverkan på dess egenfrekvenser med varierande styvhetskonstanter. Dessutom genomfördes några andra fallstudier utgående från empiriska tester samt simuleringar med hjälp av finita elementmetoden på vissa stora komponenter såsom högspänningsförgreningsdosa och batteripacken. Vibrationsprov genomfördes genom att utsätta komponenterna för Scanias nuvarande vibrationstestningsspektrum. Även vibrationsbeteendet beroende på positionen av mättningspunkterna har undersökts. Utöver det utfördes fallstudier angående termiska belastningar under vibrationstestning, tid för värmeöverföring samt energibehovet för att oscillera stora komponenter på förbestämda accelerationsnivåer. Inverkan av komponenternas storlek på deras värmeöverföringsegenskaper noterades.

A new statistical algorithm, the "modal distribution method", is proposed to statistically quantify the significance of changes in mean frequencies of individual modal vibrations of measured structural response data. In this new method, a power spectrum of measured structural response is interpreted as being a series of independent modal responses, each of which is isolated over a frequency range and treated as a statistical distribution. Pairs of corresponding individual modal distributions from different segments are compared statistically. The first version is the parametric MDM. This method is applicable to well- separated modes having Gaussian shape. For application to situations in which the signal is corrupted by noise, a new noise reduction methodology is developed and implemented. Finally, a non-parametric version of the MDM based on the Central Limit Theorem is proposed for application of MDM to general cases including closely spaced peaks and high noise. Results from all three MDMs are compared through application to simulated clean signals and the two extended MDMs are compared through application to simulated noisy signals. As expected, the original parametric MDM is found to have the best performance if underlying requirements are met: signals that are clean and have well-separated Gaussian mode shapes. In application of nonparametric methods to Gaussian modes with high noise corruption, the noise reduction MDM is found to have lower probability of false alarms than the nonparametric MDM, though the nonparametric is more efficient at detecting changes. In closely related work, the Hermite moment model is extended to highly skewed data. The aim is to enable transformation from non-Gaussian modes to Gaussian modes, which would provide the possibility of applying parametric MDM to well- separated non-Gaussian modes. A new methodology to combine statistical moments using a histogram is also developed for reliable continuous monitoring by means of MDM. The MDM is a general statistical method. Because of its general nature, it may find a broad variety of applications, but it seems particularly well suited to structural health monitoring applications because only very limited knowledge of the excitation is required, and significant changes in computed power spectra may indicate changes, such as structural damage.