Moments-Based Reduced Spectral Wave Modeling of Frequency-and-Directional Spreading Effects on Wave-Induced Longshore Currents
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 136, Issue 4
Abstract
Often, nearshore radiation stresses are approximated using the monochromatic wave assumption, although this can have significant errors when the incident waves have finite frequency and/or directional spread. Consequently, the resulting wave-driven currents could be predicted erroneously or, when fitting to observations, biased model parameters such as the bottom friction coefficient may result. We develop and test a moments-based reduced spectral wave model which includes the leading order effects of wave frequency and directional spreading. This model solves the evolution equations of wave moments, which are integrations of the wave action balance equation multiplied by weighting functions over frequencies and directions. An assumption of analytical Gaussian distribution for the frequency-direction spectrum is made to develop a simple five-parameter system that contains information on the wave height, period, direction, frequency bandwidth, and directional bandwidth. Using this model, we investigate the finite bandwidth effects on the wave field and radiation stresses. The directional spreading is found to have a strong impact on the radiation stress, with a larger directional bandwidth resulting in smaller radiation stresses. However, the frequency spreading has much less impact. The spectral wave breaking based on the roller concept is considered in this wave model. After coupling with a circulation model based on the shallow water equations, simulation results compare favorably with the DUCK94 field data for waves and longshore currents but show strong dependence on the directional bandwidth.
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Acknowledgments
Funding for this work was provided by the National Science Foundation under Grant No. NSF0423877 and from Florida Sea Grant under Grant No. UNSPECIFIEDR/C-S-46. The DUCK94 current data were downloaded from the U.S. Army Corps of Engineers Field Research Facility and were originally measured by a group including writers of Feddersen et al. (1998).
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Information
Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 136 • Issue 4 • July 2010
Pages: 200 - 214
Copyright
© 2010 ASCE.
History
Received: May 22, 2009
Accepted: Dec 2, 2009
Published online: Feb 4, 2010
Published in print: Jul 2010
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