Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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 Extreme Precipitation Projections in a Changing Climate(2019) Hu, Huiling; Ayyub, Bilal M.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Global climate is changing at an alarming rate, with an increase in heat waves, wildfires, extreme weather events, and rising sea levels, which could cost the United States billions of dollars in lost labor, reduced crop yields, flooding, health problems, and crumbling infrastructure. Reports by hundreds of US climate scientists from 13 federal agencies in the Fourth National Climate Assessment (2018) predict that the US economy will shrink by as much as 10% by the end of the century if global warming continues with current trends. Extreme precipitation, in particular, has led to significant damage through flooding, bridge scouring, land-slides, etc.; therefore, it is critical to develop accurate and reliable methods for future extreme precipitation projection. This dissertation proposes new methods of improved projections of such extremes by appropriately accounting for a changing climate. First, this dissertation studies how to model extreme precipitation using Markov Chains and dynamic optimization. By incorporating day-to-day serial dependency and dynamic optimization, the model improves the accuracy of extreme precipitation analysis significantly. The dissertation also examines future projections of extreme precipitation. State-of-the-art methods for future precipitation projections are based on downscaled Global Climate Models (GCMs), which are not always accurate for extreme precipitation projection. This work studies accuracy when using downscaled GCMs for extreme precipitation and designed new methods based on copulas to improve the accuracy. Finally, the above methods are applied to the analysis of future trends of intensity-duration-frequency (IDF) curves, which, in turn, have extensive applications in designing drainage systems. To incorporate geographic influence on local areas, a machine-learning-based solution is proposed and validated. The results show that the gradient boosting tree can be used to accurately project future IDF curves for short durations. It is also projected that short-duration intensity will increase up to 23% for the selected representative stations in this century. In summary, this dissertation systemically studies different aspects of improvements and applications of extreme precipitation projection. By using mathematical models, such as copula and Markov Chains as well as various machine-learning models (i.e., gradient boosting tree), extreme precipitation projection can be made significantly more reliable for use.Item Numerical Study of SeismicBehavior of High Strength SteelReplaceable Shear Links(2015) Hu, Huiling; Zhang, Yunfeng; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eccentrically Braced Frames (EBFs) have been widely used in seismic protection and remediation in the recent years. However, the seismic behavior of shear links made of high strength steel, which are essential "fuse" elements in EBFs, are not fully understood yet. Furthermore, most existing studies either assumed no axial load or an unrealistic constant axial load. In this numerical simulation study, two steel grades (Q460 high strength structural steel (by China standard) and ASTM A992 steel for comparison) were considered for the shear link specimens and their effects on shear link's seismic performance were numerically studied under cyclically varying lateral load along with axial force. Finite element (FE) modeling of shear link specimens with the above two steel grades were established in a general FE analysis software - ANSYS and numerical simulations are conducted on these finite element models following monotonic and cyclic loading protocols respectively. To see whether a sustainability goal of steel structure design (by saving steel use) can be achieved or not, a feasibility study of Q460 steel shear links with various section size reduction schemes are performed in this research. The numerical simulation results reveal that shear links made of Q460 high strength steel have satisfactory performance compared with A992 steel shear links, with additional benefits of material saving and weight reduction, often desired features for sustainable steel construction and replaceable fuse elements in seismic resistant structures.