Mechanical Engineering
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Item TOPOLOGICAL ANALYSIS OF DISTANCE WEIGHTED NORTH AMERICAN RAILROAD NETWORK: EFFICIENCY, ECCENTRICITY, AND RELATED ATTRIBUTES(2023) Elsibaie, Sherief; Ayyub, Bilal M.; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The North American railroad system can be well represented by a network with 302,943 links (track segments) and 250,388 nodes (stations, junctions, and waypoints), and other points of interest based on publicly accessible geographical information obtained from the Bureau of Transportation Statistics (BTS) and the Federal Railroad Administration (FRA). From this large network a slightly more consolidated subnetwork representing the major freight railroads and Amtrak was selected for analysis. Recent improvements in network and graph theory and improvements in all-pairs shortest path algorithms make it more feasible to process certain characteristics on large networks with reduced computation time and resources. The characteristics of networks at issue to support network-level risk and resilience studies include node efficiency, node eccentricity, and other attributes derived from those measures, such as network arithmetic efficiency, network geometric central node, radius, and diameter, and some distribution measures of the node characteristics. Rail distance weighting factors, representing the length of each rail line derived from BTS data, are mapped to corresponding links, and are used as link weights for the purpose of computing all pair shortest paths and subsequent characteristics. This study also compares the characteristics of North American railroad infrastructure subnetworks divided by Class I carriers, which are the largest railroad carriers classified by the Surface Transportation Board (STB) by annual operating revenue, and which together comprise most of the North American railroad network. These network characteristics can be used to inform placement of resources and plan for natural hazard and disaster scenarios. They relate to many practical applications such as network efficiency to distribute traffic and a network’s ability to recover from disruptions. The primary contribution of this thesis is the novel characterization of a detailed network representation of the North American railroad network and Class I carrier subnetworks, with established as well novel network characteristics.Item BIO-INSPIRED PUMPING MECHANISMS IN AN INTERMEDIATE REYNOLDS NUMBER(2018) Saffaraval, Farhad; Kiger, Kenneth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pumps are important to applications across a wide range of scales. Most of traditional applications occur within a range where inertia is the dominating factor influencing the pump performance, and hence many practical designs are based on mechanisms that rely on this assumption. As one moves towards smaller devices, however, the increasing effect of viscosity renders these traditional mechanisms ineffective. The current work looks towards a bio-inspired system consisting of an array of oscillating plates to contend with this challenge. The plates are placed within a channel, and the pumping performance generated is examined for a small range of Reynolds numbers intermediate between inertial and viscous regimes (0.1 < Re < 10). The goal of this work is to observe the effect of how different plate kinematics can be utilized to break the symmetry the system to produce a net pumped flow. Rigid and flexible plates are studied, using both sinusoidal and triangle wave actuation kinematics. The tests are first conducted with a single appendage, and then repeated with an array of 5 closely spaced plates to observe the effect of their interaction on the overall performance. The results of the single plate tests indicate that increased asymmetry introduced in the triangle wave actuation results in increased pumping performance as well as energy consumption. Tests were conducted at two Reynolds number conditions, Re = 0.6 and 6. The pumping performance was found to be an order of magnitude higher for the Re = 6 case. In the case of flexible plates, the results show that a mass specific pumping efficiency was higher for the flexible case with a higher frequency at the same Reynolds numbers. For the plate array, the results indicate five flexible plates with 〖∆θ〗_i=-90 will generate more than 4 times the flow rate in comparison to the single flexible plate. Asymmetric triangle actuation in conjunction with symplectic metachronal motion (〖∆θ〗_i=30) exhibits pumping performance more than 10 times of using a single rigid plate. Total work is noticeably higher for multiple plate system and will result in a reduced overall pumping efficiency in comparison to the single appendage.