http://hdl.handle.net/1903/2795 2013-06-19T23:53:32Z 2013-06-19T23:53:32Z Smoker, Jason James http://hdl.handle.net/1903/13834 2013-04-05T02:33:12Z 2012-01-01T00:00:00Z

Title: Design of a Programmable Active Acoustic Metamaterial Authors: Smoker, Jason James Abstract: Metamaterials are artificial materials engineered to provide properties which may not be readily available in nature. The development of such class of materials constitutes a new area of research that has grown significantly over the past decade. Acoustic metamaterials, specifically, are even more novel than their electromagnetic counterparts arising only in the latter half of the decade. Acoustic metamaterials provide a new tool in controlling the propagation of pressure waves. However, physical design and frequency tuning, is still a large obstacle when creating a new acoustic metamaterial. This dissertation describes active and programmable design for acoustic metamaterials which allows the same basic physical design principles to be used for a variety of application. With cloaking technology being of a great interest to the US Navy, the proposed design approach would enable the development of a metamaterial with spatially changing effective parameters while retaining a uniform physical design features. The effective parameters would be controlled by tuning smart actuators embedded inside the metamaterial structure. Since this design is based on dynamic effective parameters that can be electrically controlled, material property ranges of several orders of magnitude could potentially be achieved without changing any physical parameters. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible.

2012-01-01T00:00:00Z Konoza, Anthony http://hdl.handle.net/1903/13830 2013-04-05T02:32:27Z 2012-01-01T00:00:00Z

Title: An Evaluation of End of Maintenance Dates and Lifetime Buy Estimations for Electronic Systems Facing Obsolescence Authors: Konoza, Anthony Abstract: The business of supporting legacy electronic systems is challenging due to mismatches between the system support life and the procurement lives of the systems' constituent components. Legacy electronic systems are threatened with Diminishing Manufacturing Sources and Material Shortages (DMSMS)-type obsolescence, and the extent of their system support lives based on existing replenishable and non-replenishable resources may be unknown. This thesis describes the development of the End of Repair/End of Maintenance (EOR/EOM) model, which is a stochastic discrete-event simulation that follows the life history of a population of parts and cards and operates from time-to-failure distributions that are either user-defined, or synthesized from observed failures to date. The model determines the support life (and support costs) of the system based on existing inventories of spare parts and cards, and optionally harvesting parts from existing cards to further extend the life of the system. The model includes: part inventory segregation, modeling of part inventory degradation and periodic inventory inspections, and design refresh planning. A case study using a real legacy system comprised of 117,000 instances of 70 unique cards and 4.5 million unique parts is presented. The case study was used to evaluate the system support life (and support costs) through a series of different scenarios: obsolete parts with no failure history and never failing, obsolete parts with no failure history but immediately incurring their first failures with and without the use of part harvesting. The case study also includes analyses for recording subsequent EOM and EOR dates, sensitivity analyses for selected design refreshes that maximize system sustainment, and design refresh planning to ensure system sustainment to an end of support date. Lifetime buys refer to buying enough parts from the original manufacturer prior to the part's discontinuance in order to support all forecasted future part needs throughout the system's required support life. This thesis describes the development of the Lifetime Buy (LTB) model, a reverse-application of the EOR/EOM model, that follows the life history of an electronic system and determines the number of spares required to ensure system sustainment. The LTB model can generate optimum lifetime buy quantities of parts that minimizes the total life-cycle cost associated with the estimated lifetime buy quantity.

2012-01-01T00:00:00Z Eshaghi, Amir http://hdl.handle.net/1903/13822 2013-04-05T02:32:39Z 2012-01-01T00:00:00Z

Title: HOMOGENEOUS AND HETEROGENEOUS SENSORS FOR COMBUSTION SYSTEMS Authors: Eshaghi, Amir Abstract: Due to increasingly stringent emission regulations, it is important to develop clean combustors. Combustion behavior is very complex in almost all practical power plant systems. Measurement of temperature, pressure, local flow, and chemical composition inside the flame provides critical information to develop cleaner combustors. This would result in significant improvement in energy efficiency and reduce the environmental impact. A high density sensor network system would assist in understanding the various ongoing processes occurring within the combustors. This dissertation is focused on how much additional information can be gathered from multiple sensors. Four different time delay estimation methods (using cross correlation, phase transform, generalized cross correlation with maximum-likelihood estimation, and average square difference function) were examined using two sensors. Phase transform offered better results to calculate the time delay between a given pair of microphones. This has the potential to determine local noise generation sources from within flows and flames with the additional information on local noise generation source. As a step towards the development of a sensor network, different sensors were examined. A micro-thermocouple, microphone and microphone probes were utilized to enhance understanding of the flame with detailed information on the various ongoing processes in a premixed swirl flame. High frequency temperature and pressure measurements were used to identify the thermal and acoustic characteristics of the flame and combustor. The local distributions of fluctuating pressure and temperature were measured in different regions, in and around the flame. Pressure fluctuation showed significant variation in different directions for the combustive case relative to non-combustive flow. Also a comparison of the pressure and temperature fluctuations revealed that maximum temperature fluctuations occur mostly near to the visible flame boundary while maximum pressure fluctuation occur further away from the flame. Acoustic data from the premixed swirl combustor showed variation in fuel to air ratio changes the spatial distribution of noise as measured by different sensors placed around the combustor. A comparison of different sensors showed that a single sensor does not capture all the information with changes in fuel to air ratio.

2012-01-01T00:00:00Z Dai, Jun http://hdl.handle.net/1903/13820 2013-04-05T02:32:13Z 2012-01-01T00:00:00Z

Title: RISK ASSESSMENT AND MITIGATION OF TELECOM EQUIPMENT UNDER FREE AIR COOLING CONDITIONS Authors: Dai, Jun Abstract: In recent years, about 40% of the total energy is devoted to the cooling infrastructures in data centers. One way to save energy is free air cooling (FAC), which utilizes the outside air as the primary cooling medium, instead of air conditioning, to reduce the energy consumption to cool the data centers. Despite the energy saving, the implementation of free air cooling will change the operating environment, which may adversely affect the performance and reliability of telecom equipment. This thesis reviews the challenges and risks posed by free air cooling. The increased temperature, uncontrolled humidity, and possible contamination may cause some failure mechanisms, e.g., Conductive anodic filament (CAF) and corrosion, to be more active. If the local temperatures of some hot spots go beyond their recommended operating conditions (RoC), the performances of the equipment may be affected. In this thesis, a methodology is proposed to identify the impact of free air cooling on telecom equipment performance. It uses the performance variations under traditional air condition (A/C) to create a baseline, and compares the performance variation under variable temperature and humidity representing FAC with the baseline. This method can help data centers determine an appropriate operating environment based on the service requirements, when FAC is implemented. In addition, a statics-based approach is also developed to identify the appropriate metric for the performance variations comparison. It is the first study focusing on the impact of FAC on the telecom equipment performance. This thesis also proposes a multi-stage (design, test, and operation) approach to mitigate the reliability risks of telecom equipment under free air cooling conditions. Specifically, a prognostics-based approach is proposed to mitigate the reliability risks at operation stage, and a case study is presented to show the implementation process. This approach needn't interrupt data center services and doesn't consume additional useful life of telecom equipment. It allows the implementation of FAC in data centers which were not originally designed for this cooling method.

2012-01-01T00:00:00Z