Response of a pendulum spar to 2-dimensional random waves and a uniform current


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dc.contributor.author Rodenbusch, George
dc.date.accessioned 2007-04-03T15:30:59Z
dc.date.available 2007-04-03T15:30:59Z
dc.date.issued 1978-08
dc.identifier.uri http://hdl.handle.net/1912/1549
dc.description Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August, 1978 en
dc.description.abstract A linearized theory for the response of a circular pendulum spar in 2-dimensional waves and a uniform current is developed. The linear forces on the cylinder are predicted using an approximate potential flow theory for slender bodies. The dynamic equations are then amended to account for the wake effects of viscous bluff body flow by including a quadratic drag law and neglecting wave damping. A spectral model for the forces on a cylinder due to an oscillating wake, modeling the force as a frequency modulation process, is proposed. The non-linear equations of motion which result are then solved, assuming constant force coefficients, by linearization for use with a Gaussian random sea. The method of equivalent linearization is extended to include mean flow effects and a spatially distributed process. Some numerical experiments are then used to test the performance of the linearization. For a variety of environments, the linearization predicts the standard deviation of the simulation response to within 10% and the mean angle of inclination to within 30%. Results of the numerical experiments indicate that there is significant variation (order of magnitude changes) in both response and mean angle of inclination. Thus, significant changes are followed by the linearization. A laboratory experiment was carried out to test the linearized spar model in a realistic fluid environment. Only the low Keulegan Carpenter number regime was investigated. With some minimal manipulations, good agreement is obtained between the experiment and the linearized estimates. It appears that the drag coefficients for vortex induced in-line forces may be an order of magnitude larger than those reported in the literature, .5 instead of .06, and that the shedding of vortices due to steady flow may reduce the added mass coefficient significantly, as observed in oscillating flows with significant vortex shedding. en
dc.description.sponsorship The National Science Foundation provided tuition and stipend support under an NSF Graduate Fellowship for three years. I was fortunate to have been selected by the Board of Trustees of the Naval Postgraduate School Foundation as the first recipient of the Carl E. Menneken Fellowship for Scientific Research, which provided partial support during 1976-77. en
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en
dc.relation.ispartofseries WHOI Theses en
dc.subject Ocean waves en
dc.subject Ocean currents en
dc.subject Wakes en
dc.subject Equations of motion en
dc.subject Fluid dynamics en
dc.title Response of a pendulum spar to 2-dimensional random waves and a uniform current en
dc.type Thesis en
dc.identifier.doi 10.1575/1912/1549

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