Civil & Environmental Engineering
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Item QUANTIFYING THE ADDED VALUE OF AGILE VIEWING RELATIVE TO NON-AGILE VIEWING TO INCREASE THE INFORMATION CONTENT OF SYNTHETIC SATELLITE RETRIEVALS(2022) McLaughlin, Colin; Forman, Barton A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellite sensors typically employ a “non-agile” viewing strategy in which the boresight angle between the sensor and the observed portion of Earth’s surface remains static throughout operation. With a non-agile viewing strategy, it is relatively straightforward to predict where observations will be collected in the future. However, non-agile viewing is limited because the sensor is unable to vary its boresight angle as a function of time. To mitigate this limitation, this project develops an algorithm to model agile viewing strategies to explore how adding agile pointing into a sensor platform can increase desired information content of satellite retrievals. The synthetic retrievals developed in this project are ultimately used in an observing system simulation experiment (OSSE) to determine how agile pointing has the potential to improve the characterization of global freshwater resources.Item Scheduling under uncertainty for a Single-Hub Intermodal Freight System(2010) Markovic, Nikola; Schonfeld, Paul; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis addresses the optimization of an intermodal system with freight transfers at a single hub. It investigates the transportation processes and constraints that arise in a system's recovery after a major disruption during which backlogs have accumulated along the routes. When dealing with the backlogs, the system operator must coordinate the transportation processes and control the inflow of freight to the terminal in order to avoid overloading its storage facilities, which might reduce the throughput of the system. The coordination of transportation processes during the system's recovery can further improve the overall system performance by reducing the dwell time, increasing vehicle utilization and reducing late delivery penalties. This work focuses on the scheduling problem and develops an approach that would help the system operator reduce the overall system cost while taking into account the constraints arising in actual intermodal and intra-modal systems. Assuming that the schedule on some routes is exogenously determined and inflexible, we seek to optimize the schedules of vehicles on remaining routes. Models are developed that minimize the total cost of operating an intermodal system with freight transfers at one hub by optimizing the departure times of vehicles on the routes with flexible schedules. This model can be solved numerically without the approximations of alternative methods such as simulation. Moreover, it can be successfully applied to situations when statistical or queuing analyses are not applicable due to the small number of events (vehicle arrivals). We specifically analyze an intermodal system consisting of multiple feeder truck routes and multiple main airline routes. The specific example of two transportation modes was used to make the development and application of the model easier to understand. However, the mathematical model developed in this thesis is applicable to any other combination of transportation modes using discrete vehicles.Item Scheduling Deliveries with Backhauls in Thailand's Cement Industry(2011) Paraphantakul, Chutipong; Miller-Hooks, Elise; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this study, the Truckload Delivery with Backhaul Scheduling Problem (TDBSP) is formulated and an Ant Colony Optimization methodology developed for a related problem, the Vehicle Routing Problem with Backhaul and Time Windows (VRPBTW), is adapted for its solution. The TDBSP differs from the VRPBTW in that shipments are in units of truckloads, multiple time windows in multiple days are available for delivery to customers, limited space for servicing customers is available and multiple visits to each customer may be required. The problem is motivated by a real-world application arising at a leading cement producer in Thailand. Experts at the cement production plant assign vehicles to cement customers and lignite mines based on manual computations and experience. This study provides mathematical and computational frameworks for modeling and solving this real-world application.Item Assessing CPM Scheduling Software For The Small to Mid-Size Construction Firm(2007-12-11) Hawkins, Craig Vernon; O'Connell, Kenneth J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An analysis of the results of a regional survey and a comparison of three commonly used programs, SureTrak, Primavera Contractor, and Microsoft (MS) Project, was undertaken. Selected because of their comparable cost structure and their wide acceptance in the industry, these three programs were evaluated on the basis of the features construction managers use to manage their projects. The results indicate that each program had many benefits. However, MS Project and Primavera Contractor both scored better than SureTrak on the overall rating. MS project also scored best in terms of ease of use. It must be noted that this study is based on a comparison of use on relatively small projects (approximately $500,000 in final value and four months duration) and that the results on larger, more complex projects might be different.