http://hdl.handle.net/1957/14320 2013-05-24T19:04:23Z http://hdl.handle.net/1957/38586 Volume displacement effects during bubble entrainment in a travelling vortex ring Cihonski, Andrew J.; Finn, Justin R.; Apte, Sourabh V. When a few bubbles are entrained in a travelling vortex ring, it has been shown that, even at extremely low volume loadings, their presence can significantly affect the structure of the vortex core (Sridhar & Katz, J. Fluid Mech., vol. 397, 1999, pp. 171-202). A typical Euler-Lagrange point-particle model with two-way coupling for this dilute system, wherein the bubbles are assumed subgrid and momentum point sources are used to model their effect on the flow, is shown to be unable to capture accurately the experimental trends of bubble settling location, bubble escape and vortex distortion for a range of bubble parameters and vortex strengths. The bubbles experience significant amounts of drag, lift, added mass, pressure and gravity forces. However, these forces are in balance with each other as the bubbles reach a mean settling location away from the vortex core. The reaction force on the fluid due to the net summation of these forces alone is thus very small and is unable to affect the vortex core. By accounting for fluid volume displacement due to bubble motion, experimental trends on vortex distortion and bubble settling location are captured accurately. The fluid displacement effects are studied by computing various contributions to an effective volume displacement force and are found to be important even at low volume loadings. As the bubble size and hence bubble Reynolds number increase, the bubbles settle further away from the vortex centre and have strong potential for vortex distortion. The net volume displacement force depends on the radial pressure force, the radial settling location of the bubble, as well as the vortex Reynolds number. The resultant of the volume displacement force is found to be roughly at 45 degrees with the vortex travel direction, resulting in wakes directed towards the vortex centre. Finally, a simple modification to the standard point-particle two-way coupling approach is developed wherein the interphase reaction source terms are consistently altered to account for the fluid displacement effects and reactions due to bubble accelerations. This is the publisher’s final pdf. The published article is copyrighted by Cambridge University Press and can be found at: http://www.cambridge.org/. 2013-03-13T00:00:00Z http://hdl.handle.net/1957/38433 Mixed fleet dispatching in truckload relay network design optimization Vergara, Hector A.; Root, Sarah We propose a mathematical formulation for strategic relay network design and dispatching method selection for full truckload transportation. The proposed model minimizes total transportation and installation costs of a mixed fleet dispatching system combining relay network and point-to-point dispatching. Operational constraints such as maximum driver tour length and load circuity are considered within the variable definition using predefined templates to generate feasible routes. High quality solutions for largely-sized problem instances are obtained in reasonable times. Computational results are analyzed to develop insights about the mixed fleet dispatching system and quantify its benefits over relay network-only and point-to-point dispatching. This is the author's version of a work that was accepted for publication in Transportation Research Part E. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Transportation Research Part E, 54 (2013), pp. 32-49 DOI information: 10.1016/j.tre.2013.04.001 2013-08-01T00:00:00Z http://hdl.handle.net/1957/37952 Geometric Visualization of Self-Propulsion in a Complex Medium Hatton, Ross L.; Ding, Yang; Choset, Howie; Goldman, Daniel I. Combining geometric mechanics theory, laboratory robotic experiment, and numerical simulation, we study the locomotion in granular media of the simplest noninertial swimmer, the Purcell three-link swimmer. Using granular resistive force laws as inputs, the theory relates translation and rotation of the body to shape changes (movements of the links). This allows analysis, visualization, and prediction of effective movements that are verified by experiment. The geometric approach also facilitates comparison between swimming in granular media and in viscous fluids. DOI: 10.1103/PhysRevLett.110.078101 This is the publisher’s final pdf. The published article is copyrighted by American Physical Society and can be found at: http://www.aps.org/. 2013-02-14T00:00:00Z http://hdl.handle.net/1957/37557 Fatigue threshold R-curves predict small crack fatigue behavior of bridging toughened materials Gallops, S.; Fett, T.; Ager, J. W., III; Kruzic, J. J. Small crack fatigue is a widely recognized problem in the fatigue of materials; however, there has been limited progress in developing methods for predicting small crack fatigue behavior. In this paper, small crack effects due to crack bridging are addressed. A fatigue threshold R-curve was measured for a 99.5% pure polycrystalline alumina using standard compact tension specimens and it was used to 1) determine the bridging stress profile for the material and 2) make fatigue endurance strength predictions for realistic semi-elliptical surface cracks. Furthermore, is has been shown that the fatigue threshold R-curve can equivalently be determined by measuring the bridging stress distribution, in this case using fluorescence spectroscopy, using only a long crack compact tension specimen without the need for difficult small crack experiments. It is expected that this method will be applicable to a wide range of bridging toughened materials, including composites, toughened ceramics, intermetallics, and multi-phase materials. This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/acta-materialia/. 2011-12-01T00:00:00Z