UMD Theses and Dissertations
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Item GEOSTATISTICAL ESTIMATION OF BLUE CRAB CALLINECTES SAPIDUS ABUNDANCE IN CHESAPEAKE BAY AT LOCAL SCALES(2022) Jones, Sarah Ann; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increases in the sizes of container ships due to the expansion of the Panama Canal has increased the need for dredging activities in the Chesapeake Bay. Placement of dredged material in the Bay is restricted to winter months owing to concerns for threatened and endangered species. Placement of dredged material in the lower Chesapeake Bay in Wolf Trap Alternate Open Water Placement Site (WTAPS) overlaps with overwintering locations for mature female blue crab. To estimate the potential magnitude of winter mortality in WTAPS and WTAPS Northern Extension (WTAPSNE) resulting from placement of dredged material, a range of geostatistical tools (e.g., inverse distance weighting and kriging) were used to map the distribution and estimate the abundance of blue crab in Chesapeake Bay, WTAPS, and WTAPSNE (i.e., small-scale estimation) from 1990–2020 using data from the winter dredge survey. These analyses indicated that a low proportion of the age-1+ female blue crab population occurs within WTAPS and WTAPSNE (<1.18% and <1.5% respectively). Variability of abundance estimates was high when female age-1+ abundance was less than 150 million in the Chesapeake Bay. Therefore, we suggest the Port limit placement of dredged materials in WTAPS and WTAPSNE when female age-1+ abundance is less than 150 million; we recommend the Port not undertake placement activities when the stock is declared overfished (i.e., when female age-1+ abundance is less than 72.5 million).Item Single and Multiresponse Adaptive Design of Experiments with Application to Design Optimization of Novel Heat Exchangers(2009) Aute, Vikrant Chandramohan; Azarm, Shapour; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Engineering design optimization often involves complex computer simulations. Optimization with such simulation models can be time consuming and sometimes computationally intractable. In order to reduce the computational burden, the use of approximation-assisted optimization is proposed in the literature. Approximation involves two phases, first is the Design of Experiments (DOE) phase, in which sample points in the input space are chosen. These sample points are then used in a second phase to develop a simplified model termed as a metamodel, which is computationally efficient and can reasonably represent the behavior of the simulation response. The DOE phase is very crucial to the success of approximation assisted optimization. This dissertation proposes a new adaptive method for single and multiresponse DOE for approximation along with an approximation-based framework for multilevel performance evaluation and design optimization of air-cooled heat exchangers. The dissertation is divided into three research thrusts. The first thrust presents a new adaptive DOE method for single response deterministic computer simulations, also called SFCVT. For SFCVT, the problem of adaptive DOE is posed as a bi-objective optimization problem. The two objectives in this problem, i.e., a cross validation error criterion and a space-filling criterion, are chosen based on the notion that the DOE method has to make a tradeoff between allocating new sample points in regions that are multi-modal and have sensitive response versus allocating sample points in regions that are sparsely sampled. In the second research thrust, a new approach for multiresponse adaptive DOE is developed (i.e., MSFCVT). Here the approach from the first thrust is extended with the notion that the tradeoff should also consider all responses. SFCVT is compared with three other methods from the literature (i.e., maximum entropy design, maximin scaled distance, and accumulative error). It was found that the SFCVT method leads to better performing metamodels for majority of the test problems. The MSFCVT method is also compared with two adaptive DOE methods from the literature and is shown to yield better metamodels, resulting in fewer function calls. In the third research thrust, an approximation-based framework is developed for the performance evaluation and design optimization of novel heat exchangers. There are two parts to this research thrust. First, is a new multi-level performance evaluation method for air-cooled heat exchangers in which conventional 3D Computational Fluid Dynamics (CFD) simulation is replaced with a 2D CFD simulation coupled with an e-NTU based heat exchanger model. In the second part, the methods developed in research thrusts 1 and 2 are used for design optimization of heat exchangers. The optimal solutions from the methods in this thrust have 44% less volume and utilize 61% less material when compared to the current state of the art microchannel heat exchangers. Compared to 3D CFD, the overall computational savings is greater than 95%.Item SPATIAL ECOLOGY OF BLUE CRAB (CALLINECTES SAPIDUS) IN CHESAPEAKE BAY(2004-11-12) Jensen, Olaf Peter; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spatial heterogeneity is a striking feature of the blue crab life history and fisheries in Chesapeake Bay. However, a quantitative assessment of their spatial distribution and the factors controlling it has been lacking. Based on 13 years of data from a baywide winter dredge survey, geostatistical and two-stage generalized additive models (GAMs) are used to characterize blue crab distributions and investigate environmental factors responsible for the distribution of mature females, respectively. A landscape-based distance metric, the "Lowest-Cost Path" (LCP) distance, is developed as an alternative to Euclidean distance for kriging in estuaries. Estimates of variogram parameters differed significantly between the two metrics but kriging accuracy did not. Geostatistical abundance estimates show significant declines from 1990 to 2002. The observed relationship between changes in distribution and changes in abundance is suggestive of density-dependent habitat selection. Depth and distance from the Bay mouth were the most important predictors of mature female abundance.