Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Fault Detection on a Full-Scale OH-58 A/C Helicopter Transmission(2010) Hood, Adrian Alexander; Pines, Darryll J.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Detecting seeded faults on a full-scale helicopter transmission is the focus of this work. Methods to isolate the dynamics of an individual sun gear, in an effort to assess its condition, are developed and validated on an OH-58 helicopter transmission's planetary reduction stage. This area has been shown to be challenging because the planetary system does not allow for direct measurements of the sun gear. Instead, special measurement and data processing techniques are needed to filter out the effects of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Planetary indexing is used to geometrically synchronize dynamic measurements with the meshing tooth's position along its pressure line. This provides the opportunity for source/signal mapping that can lead to increased sensitivity, allowing faults to be detected early and thus increasing the available time for corrective action. Accelerometers mounted along the transmission housing, acoustic transducers distributed about the test cell, and an oil debris monitoring system are all used to analyze three seeded fault cases. Transmission components, (two sun gears and a single planet bearing), which were damaged in previous fatigue tests, serve as the focus of this current work. Two vibration separation (VS) algorithms, tailored to the three planet OH-58A, and the four planet, non-sequential OH-58C transmissions, were developed and their resulting signals analyzed. In addition, a geometrically synchronized measurement method to transmission diagnostics is also developed. This non-VS based method uses only the time synchronously averaged data and takes advantage of signal/source mapping required for VS. Eleven commonly used condition indicators are used on both global and separated signals and their results tabulated. All three damage detection algorithms were successful in identifying the damage on the sun gear with multiple faults. Sun gear damage was confirmed by the presence of sun mesh groups. Detecting the single tooth spall continues to be a challenge. Also demonstrated is the ability for the vibration separation methods developed to isolate components. Safety and cost are the main motivators for helicopter Health Usage and Monitoring Systems (HUMS). During flight, critical components are subjected to sustained vibratory and impulsive loads requiring the need for frequent inspections. Methods that can reduce this time and effectively detect faults in their infancy are highly sought. Actively monitoring the transmission's health can provide the benefit of detecting damage early and possibly avoid catastrophe. In addition, active monitoring provides an updated assessment of a component's condition which can possibly increase its life when compared to scheduled replacement times. The methods proposed for gear tooth diagnostics can be integrated in an overall helicopter HUMS program with the main objective of cost-effectively improving the safety of both civil and military helicopters while reducing the cost of ownership.Item PROGNOSTICS DEMONSTRATION OF ELECTRONIC COMPONENTS SUBJECTED TO VIBRATION ENVIRONMENT OF A LIGHT MILITARY TACTICAL VEHICLE(2007-11-05) Yu, Alan; Barker, Donald B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A demonstration of the Prognostics and Health Management (PHM) method in a military vehicle environment was performed. The purpose of the demonstration is to show rapid and cost effective means to increase reliability and effectiveness of in-cabin equipment through PHM implementation. The PHM method allows for prediction of damage accumulation in a system while in its operating environment. Prediction is achieved by monitoring and assessing appropriate product parameters. An experimental setup to perform in-cabin accelerated testing on printed circuit boards (PCB) was developed. Strain, acceleration, continuity, and GPS data were recorded during testing. Using recorded data, life prediction with cycle counting and PSD load blocking techniques was demonstrated for BGA components. A limited set of terrain and loading conditions was characterized using Root Mean Square (RMS) and Power Spectral Density (PSD).Item Prognostics and Health Management of Electronics by Utilizing Environmental and Usage Loads(2006-07-06) Vichare, Nikhil Manohar; Pecht, Michael G; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prognostics and health management (PHM) is a method that permits the reliability of a system to be evaluated in its actual application conditions. Thus by determining the advent of failure, procedures can be developed to mitigate, manage and maintain the system. Since, electronic systems control most systems today and their reliability is usually critical for system reliability, PHM techniques are needed for electronics. To enable prognostics, a methodology was developed to extract load-parameters required for damage assessment from irregular time-load data. As a part of the methodology an algorithm that extracts cyclic range and means, ramp-rates, dwell-times, dwell-loads and correlation between load parameters was developed. The algorithm enables significant reduction of the time-load data without compromising features that are essential for damage estimation. The load-parameters are stored in bins with a-priori calculated (optimal) bin-width. The binned data is then used with Gaussian kernel function for density estimation of the load-parameter for use in damage assessment and prognostics. The method was shown to accurately extract the desired load-parameters and enable condensed storage of load histories, thus improving resource efficiency of the sensor nodes. An approach was developed to assess the impact of uncertainties in measurement, model-input, and damage-models on prognostics. The approach utilizes sensitivity analysis to identify the dominant input variables that influence the model-output, and uses the distribution of measured load-parameters and input variables in a Monte-Carlo simulation to provide a distribution of accumulated damage. Using regression analysis of the accumulated damage distributions, the remaining life is then predicted with confidence intervals. The proposed method was demonstrated using an experimental setup for predicting interconnect failures on electronic board subjected to field conditions. A failure precursor based approach was developed for remaining life prognostics by analyzing resistance data in conjunction with usage temperature loads. Using the data from the PHM experiment, a model was developed to estimate the resistance based on measured temperature values. The difference between actual and estimated resistance value in time-domain were analyzed to predict the onset and progress of interconnect degradation. Remaining life was predicted by trending several features including mean-peaks, kurtosis, and 95% cumulative-values of the resistance-drift distributions.