http://dspace.library.cornell.edu The eCommons@Cornell digital repository system captures, stores, indexes, preserves, and distributes digital research material. Search the Channel search http://dspace.library.cornell.edu/simple-search http://hdl.handle.net/1813/11499 Title: Rythms of a Saline Oscillator <br/> <br/>Authors: Carreno Rodriguez, Alejandro; Salazar Romero, Yadira; Garcia Ruiz, Jaime; Stern Forgach, Catalina <br/> <br/>Abstract: A small vase with a saline solution and a small hole in the bottom is partially submerged in a larger container filled with distilled water. Various periodic regimes of exchange of water between containers can be established. The motion starts with a jet of salt water falling into the distilled water. After sometime, the apparently stationary motion breaks up and a jet of distilled water starts going up into the salt water, and a periodic regime is established for some time. The time for the initial discharge is much longer than the following oscillations. Eventually, the oscillation becomes asymmetric but it can last for over a day. Distilled water accumulates on top of the small container and salt water on the bottom of the large container until the motion stops. The frequency of oscillation depends on the area ratios, the relative volumes of water and the size of the hole. When perturbed, different regimes can be observed. The behavior can be compared to a Rayleigh oscillator. We thank the support of UNAM through project PAPIME PE104907. http://hdl.handle.net/1813/11498 Title: Pattern formation by oscillating flows <br/> <br/>Authors: Centeno Sierra, Mariana; Martinez Farias, Francisco Javier; Hernandez Tahuilan, Jorge; Stern Forgach, Catalina <br/> <br/>Abstract: A tube with a diffuser is partially submerged in a water tank. A piston, inside the tube, creates an oscillating flow. The curvature of the diffuser is such that no vortices are formed inside. A vortex is formed when the flow gets out of the diffuser and another when it goes in. The path of these vortices when they go out of the diffuser strongly depends on the amplitude and frequency of oscillation forming a large variety of flow patterns. We thank the support of UNAM through project PAPIME PE104907 http://hdl.handle.net/1813/11497 Title: Rythms of a Saline Oscillator <br/> <br/>Authors: Carreno Rodriguez, Alejandro; Salazar Romero, Yadira; Garcia Ruiz, Jaime; Stern Forgach, Catalina <br/> <br/>Abstract: A small vase with a saline solution and a small hole in the bottom is partially submerged in a larger container filled with distilled water. Various periodic regimes of exchange of water between containers can be established. The motion starts with a jet of salt water falling into the distilled water. After sometime, the apparently stationary motion breaks up and a jet of distilled water starts going up into the salt water, and a periodic regime is established for some time. The time for the initial discharge is much longer than the following oscillations. Eventually, the oscillation becomes asymmetric but it can last for over a day. Distilled water accumulates on top of the small container and salt water on the bottom of the large container until the motion stops. The frequency of oscillation depends on the area ratios, the relative volumes of water and the size of the hole. When perturbed, different regimes can be observed. The behavior can be compared to a Rayleigh oscillator. We thank the support of UNAM through project PAPIME PE104907. http://hdl.handle.net/1813/11496 Title: The time evolution of vortical structures in the swimming of weakly electric fish <br/> <br/>Authors: Shirgaonkar, Anup A.; Curet, Oscar M.; Patankar, Neelesh A.; MacIver, Malcolm A. <br/> <br/>Abstract: The gymnotiform mode of aquatic locomotion is characterized by the use of an elongated anal fin, generically referred to as a ribbon fin. The extraordinarily maneuverable weakly electric black ghost knifefish (Apteronotus albifrons) uses this mode of locomotion. These animals also have an unusual sensory adaptation: the use of a self-generated electric field to detect surrounding objects. This allows them to hunt at night in the murky waters of Amazon Basin rivers, where they are indigenous. Electric fish are a leading model system within neurobiology for the study of the neural control of sensing and movement. These animals also offer a unique opportunity to develop novel sensing and propulsion technologies for use in systems such as underwater vehicles. The knifefish sends continuous sinusoidal traveling waves along the fin. By altering the direction of the traveling wave, it swims backward as gracefully as it swims forward, and frequently reverses the direction of swimming during natural behaviors such as prey capture. In order to better understand how the fish controls its movement, we are studying the hydrodynamics of ribbon fin propulsion. We investigated the mechanism of propulsive force generation by a non-translating, non-rotating ribbon fin - the situation relevant to the low-speed, rapid forward-backward maneuvers of the knifefish. Using flow visualizations of numerical simulation data [1], we found that the fin generates both surge force (equivalently, thrust, i.e. the propulsive force in the swimming direction), and heave force (force in the perpendicular direction). The thrust generation mechanism involves the generation of a longitudinal, central jet running along the lower end of the fin, and an associated series of vortex rings attached to the lower edge of the fin. Smaller secondary vortex rings were observed to be emitted at an angle to the swimming direction on both sides of the fin surfaces. This indicates that the peculiar combination of the morphology and the actuation pattern of the fin (traveling waves) of the knifefish may be utilized by the animal to generate significant sideways forces for rapid maneuvers. The mechanism of heave generation consists of longitudinally oriented vortex rolls shedding at the lower edge of the ribbon-fin [1]. The central jet becomes further evident from the velocity blobs that are advected down the length of the fin. This ``bucket effect?? gives rise to fluid carried by successive crests and troughs of the fin-wave and expelled into the surrounding fluid at the trailing edge of the fin. This results in an undulatory propulsive force. [1.] A. A. Shirgaonkar, O. M. Curet, N. A. Patankar, M. A. MacIver, The hydronamics of ribbon-fin propulsion during impulsive motion, Journal of Experimental Biology