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Dynamics of the nearshore wave bottom boundary layer

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dc.contributor.advisor Holman, Robert A.
dc.creator Foster, Diane Lyn
dc.date.accessioned 2012-10-12T18:53:59Z
dc.date.available 2012-10-12T18:53:59Z
dc.date.copyright 1996-06-13
dc.date.issued 1996-06-13
dc.identifier.uri http://hdl.handle.net/1957/34380
dc.description Graduation date: 1997 en_US
dc.description.abstract This thesis presents an examination of the nearshore wave bottom boundary layer under conditions of significant sediment response. Using both field observations and simple models, the response of the bottom boundary layer to random waves is shown to have a complex behavior. First, the linearized wave bottom boundary layer governing equation is solved with a transformation of the cross-shore velocity to a distorted spatial domain, resulting in an analytic expression for the temporal and vertical structure of the cross-shore velocity under an arbitrary wave field. Model predictions of the bed shear velocity are in good agreement with laboratory measurements. The model is limited by assuming zero velocity at a fixed bed and that turbulence generation is solely due to bottom shear. Next, a comprehensive set of near bed cross-shore velocity, sediment suspension, and bed elevation observations, collected in 2 m water depth on the North Carolina coast, are presented. The observations show a cross-shore velocity structure which decays with increasing proximity to the bed as predicted by simple theory. Bottom shears based on rms amplitude decay and time-averaged phase shifts are lower than model predictions and may be indicative of more rapid mixing of momentum than assumed in the above model. Also, frequency-dependent estimates of the phase and amplitude vertical structure show a nonlinear response of the wave bottom boundary layer over the incident band. Through most flow phases, estimates of turbulent kinetic energy increase linearly from the bed, however under large wave crests, enhanced turbulence levels are observed and are well correlated to active sediment suspension events. Estimates of dissipation rates are significantly less than those observed in an actively breaking surf zone wave, and significantly greater than those observed in ocean boundary layers, and continental shelf current boundary layers. Finally, an Oregon coast field experiment showed an intermittent high frequency velocity variance structure which was correlated to suspended sediment events. A linear shear instability analysis determined that during the period of flow reversal there exists a potential for generating turbulence due to shear instabilities of the vertical structure of cross-shore velocity. en_US
dc.language.iso en_US en_US
dc.subject.lcsh Ocean waves -- Mathematical models en_US
dc.title Dynamics of the nearshore wave bottom boundary layer en_US
dc.type Thesis/Dissertation en_US
dc.degree.name Doctor of Philosophy (Ph. D.) in Civil Engineering en_US
dc.degree.level Doctoral en_US
dc.degree.discipline Engineering en_US
dc.degree.grantor Oregon State University en_US
dc.contributor.committeemember Lunch, Bill
dc.description.digitization File scanned at 300 ppi (Monochrome, 256 Grayscale) using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR. en_US
dc.description.peerreview no en_us

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