Master of Science in Engineering - Engineering / In this thesis, laser-triggering of spark gaps was investigated. In other words, the purpose of the project, was to ascertain what type of laser (in terms of wavelength, energy and pulse width) is the most efficient to accomplish elec-trical breakdown across a short spark gap. The spark gap used was set up in a coaxial geometry and the gap length was able to vary from 20 mm to 2.5 mm or less. Two lasers were used: A KrF excimer (248 nm - UV) and an Nd:YAG (1064-532-355 nm). Experiments showed that a gap of 5 mm in air and a focusing lens of 100 mm, yielded the best (widest) voltage breakdown range. It was found that the key element that will ensure electrical breakdown in a spark gap, was power density (W/cm2). A power density of about 10 GW/cm2 is needed to create a spark in air. In the case of the KrF laser, the voltage range was found to be 2-13 kV (216 mJ/pulse). In the case of the YAG laser operating at 1064 nm (170 mJ/pulse), the range was 600 V-13 kV and for 532 nm (40 mJ/pulse), 3 kV-13 kV. The wavelength of the laser did effect the result. For 1064 nm, breakdown in air occured at 70 mJ, whereas at 532 nm, breakdown occured at 40 mJ. For the case where the SF6 gap was used, the range was found to be much larger than in the case of air. This can be attributed to the sensitivity of this gas to high intensity electric fields.

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To efficiently capture signal events when performing analog measurements, a competent toolbox is required. In this master thesis, a system for frequency domain triggering is designed and implemented. The implemented system provides advanced frequency domain trigger conditions, in order to ease the capture of a desired signal event. A real-time 1024-point pipelined feedforward FFT-core is implemented to transform the signal from the time domain to the frequency domain. The system is designed and synthesized for a Virtex-6 FPGA (XC6VLX240T) and is integrated into SP Devices’ digitizer ADQ1600. The implemented system is able to handle a continuous stream of 1.6GS/s at 16-bit. A small software API is developed that provides runtime configuration of the Triggering conditions.

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Proefschrift Universiteit Maastricht. / Auteursnaam op omslag: Marieke de Groot. Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

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Soil liquefaction continues to be one of the leading causes of ground failure during earthquakes, resulting in significant damage to infrastructure around the world. The study presented herein aims to develop improved methodologies for predicting liquefaction triggering and the consequent damage potential such that the impacts of liquefaction on natural and built environment can be minimized. Towards this end, several research tasks are undertaken, with the primary focus being the development of a framework that consistently and sufficiently accounts for the mechanics of liquefaction triggering and surface manifestation. The four main contributions of this study include: (1) development of a framework for selecting an optimal factor of safety (FS) threshold for decision making based on project-specific costs of mispredicting liquefaction triggering, wherein the existing stress-based "simplified" model is used to predict liquefaction triggering; (2) rigorous investigation of manifestation severity index (MSI) thresholds for distinguishing cases with and without manifestation as a function of the average inferred soil-type within a soil profile, which may be employed to more accurately estimate liquefaction damage potential at sites having high fines-content, high plasticity soils; (3) development of a new manifestation model, termed Ishihara-inspired Liquefaction Severity Number (LSNish), that more fully accounts for the effects of non-liquefiable crust thickness and the effects of contractive/dilative tendencies of soil on the occurrence and severity of manifestation; and (4) development of a framework for deriving a "true" liquefaction triggering curve that is consistent with a defined manifestation model such that factors influential to triggering and manifestation are handled more rationally and consistently. While this study represents significant conceptual advance in how risk due to liquefaction is evaluated, additional work will be needed to further improve and validate the methodologies presented herein. / Doctor of Philosophy / Soil liquefaction continues to be one of the leading causes of ground failure during earthquakes, resulting in significant damage to infrastructure around the world (e.g., the 2010-2011 Canterbury earthquake sequence in New Zealand, 2010 Maule earthquake in Chile, and the 2011 Tohoku earthquake in Japan). Soil liquefaction refers to a condition wherein saturated sandy soil loses strength as a result of earthquake shaking. Surface manifestations of liquefaction include features that are visible at the ground surface such as sand boils, ejecta, cracks, and settlement. The severity of manifestation is often used as a proxy for damage potential of liquefaction. The overarching objective of this dissertation is to develop improved models for predicting triggering (i.e., occurrence) and surface manifestation of liquefaction such that the impacts of liquefaction on the natural and built environment can be minimized. Towards this end, this dissertation makes the following main contributions: (1) development of an approach for selecting an appropriate factor of safety (FS) against liquefaction for decision making based on project-specific consequences, or costs of mispredicting liquefaction; (2) development of an approach that allows better interpretations of predictions of manifestation severity made by the existing models in profiles having high fines-content, high plasticity soil strata (e.g., clayey and silty soils), given that the models perform poorly in such conditions; (3) development of a new model for predicting the severity of manifestation that more fully accounts for factors controlling manifestation; and (4) development of a framework for predicting liquefaction triggering and surface manifestation such that the distinct factors influential to each phenomenon are handled more rationally and consistently.

Temporally and spatially clustered earthquake sequences along plate boundary zones indicate that patterns of seismicity may be influenced by earthquake-induced stress changes. Many studies invoke Coulomb stress change (CSC) as one possible geo-mechanical mechanism to explain stress interactions between earthquakes, their aftershocks, or large subsequent earthquakes; however, few address the statistical robustness of CSC triggering beyond spatial correlations. To address this, I evaluate the accuracy of CSC predictions in subduction zones where Earth’s largest earthquakes occur and generate voluminous and diverse aftershock sequences. A series of synthetic tests are implemented to investigate the accuracy of inferred stress changes predicted by slip distributions inverted from suites of geodetic observations (InSAR, GPS, seafloor geodetic observations) that are increasingly available for subduction zone earthquakes. Through these tests, I determine that inferred stress changes are accurately predicted at distances greater than a critical distance from modeled slip that is most dependent on earthquake magnitude and the proximity of observations to the earthquake itself. This methodology is then applied to the 2010 Mw 8.8 Maule, Chile earthquake sequence to identify aftershocks that may be used to perform statistically robust tests of CSC triggering; however, only 13 aftershocks from a population of 475 events occurred where confidence in CSC predictions is deemed to be high. The inferred CSC for these events exhibit large uncertainties owing to nodal plane uncertainties assigned to the aftershock mechanisms. Additionally, tests of multiple published slip distributions result in inconsistent stress change predictions resolved for the 13 candidate aftershocks. While these results suggest that CSC imparted by subduction megathrust earthquakes largely cannot be resolved with slip distributions inverted from terrestrial geodetic observations alone, the synthetic tests suggest that dramatic improvements can be made through the inclusion of near-source geodetic observations from seafloor geodetic networks. Furthermore, CSC uncertainties will likely improve with detailed earthquake moment tensor catalogs generated from dense regional seismic networks.

Electric power utilities and end users are becoming increasingly concerned about the quality of power supply. To reduce the losses caused by power service disturbances, mitigation devices are available for improving the power quality. The first step in the power quality improvement is to monitor the system behavior by using some Electronic recording devices. A design and implementation of a digital signal processor based power quality monitoring device is presented in this thesis. Several event-triggering methods are studied and implemented to detect system disturbances. Simulation and test results indicate that the proposed design can meet the requirements for power measurements and transient event recording during steady and transient states.