Oscillating foils of high propulsive efficiency

Thrust-producing harmonically oscillating foils are studied through force and power measurements, as well as visualization data, to classify the principal characteristics of the flow around and in the wake of the foil. Visualization data are obtained using digital particle image velocimetry at Reynolds number 1100, and force and power data are measured at Reynolds number 40 000. The experimental results are compared with theoretical predictions of linear and nonlinear inviscid theory and it is found that agreement between theory and experiment is good over a certain parametric range, when the wake consists of an array of alternating vortices and either very weak or no leading-edge vortices form. High propulsive efficiency, as high as 87%, is measured experimentally under conditions of optimal wake formation. Visualization results elucidate the basic mechanisms involved and show that conditions of high efficiency are associated with the formation on alternating sides of the foil of a moderately strong leading-edge vortex per half-cycle, which is convected downstream and interacts with trailing-edge vorticity, resulting eventually in the formation of a reverse Karman street. The phase angle between transverse oscillation and angular motion is the critical parameter affecting the interaction of leading-edge and trailing-edge vorticity, as well as the efficiency of propulsion

Ontology and Metadata Creation for the Poseidon Distributed Coastal Zone Management System

The objective of the Poseidon Coastal Zone Management System project is to develop a distributed data and software architecture to locate, retrieve, utilize (in simulations and analysis), and visualize information about the coastal ocean environment. The work described in this paper concentrates on the issues related to efficiently identifying and creating the data needed for a given task. Since scientific data sets often do not contain information about the environment in which the data was obtained, we need a method of distinguishing data based on external information, or metadata. This metadata needs to be standardized in order to facilitate searching. While many metadata standards exist, no one of them is adequate for representing all the information needed for coastal zone management. We have therefore implemented a method that incorporates three existing metadata standards in an expandable object-oriented structure known as the Warwick Framework. Furthermore, since metadata is ex..