Computational Fluid Dynamics Simulations of Oscillating Wings and Comparison to Lifting-Line Theory

Computational fluid dynamics (CFD) analysis was performed in order to compare the solutions of oscillating wings with Prandtl’s lifting-line theory. Quasi-steady and steady-periodic simulations were completed using the CFD software Star-CCM+. The simulations were performed for a number of frequencies in a pure plunging setup. Additional simulations were then completed using a setup of combined pitching and plunging at multiple frequencies. Results from the CFD simulations were compared to the quasi-steady lifting-line solution in the form of the axial-force, normal-force, power, and thrust coefficients, as well as the efficiency obtained for each simulation. The mean values were evaluated for each simulation and compared to the quasi-steady lifting-line solution. It was found that as the frequency of oscillation increased, the quasi-steady lifting-line solution was decreasingly accurate in predicting solutions

Patterns of tooth replacement in osteichthyans: variations on a theme

Nonmammalian tooth-bearing vertebrates usually replace their teeth throughout life. Much about how a replacement pattern is generated has been learned from zebrafish. However, to understand general mechanisms of tooth replacement, advantage can be taken from studying other, “nonmodel” species. We have mapped the patterns of tooth replacement in widely divergent aquatic osteichthyans using 2D charts, in which one axis is time, the other linear spacing along the tooth row. New teeth that are generated simultaneously are considered part of the same odontogenic wave. Using this approach, it appears that a similar, general pattern underlies very distinctive dentitions in distantly related species. A simple shift in spacing of odontogenic waves, or in distance between subsequent tooth positions along a row (or both), can produce dramatically different dentitions between life stages within a species, or between closely related species. Examples will be presented from salmonids, cyprinids, and cichlids. Our observations suggest that lines linking subsequent positions may have more biological significance than replacement waves (usually linking alternate positions), often used to explain the generation of patterns. The presence of a general pattern raises questions about common control mechanisms. There is now increasing evidence, at least for the zebrafish, to support a role for stem cells in continuous tooth renewal and control of replacement patterns