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The Interaction Between Short Ocean Swell and Transient Long Waves – An Experimental Study

The Interaction Between Short Ocean Swell and Transient Long Waves – An Experimental Study. James Kaihatu , Deirdre Devery , Richard Irwin and John goertz Coastal and Ocean Engineering division Zachry Department of Civil engineering Texas a&m university College station, tx , USA.

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The Interaction Between Short Ocean Swell and Transient Long Waves – An Experimental Study

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  1. The Interaction Between Short Ocean Swell and Transient Long Waves – An Experimental Study James Kaihatu, Deirdre Devery, Richard Irwin and John goertz Coastal and Ocean Engineering division Zachry Department of Civil engineering Texas a&m university College station, tx, USA

  2. Outline • Short wave-long wave interaction • Experiments • Dissipation analysis • Dissipation coefficient vs. spectral shape • Energy flux estimates • Wavelet transforms • Breaking Parameter • Wavelet bicoherence • Conclusions • Future Work

  3. Introduction • How does the coexistence of transient long waves and short waves affect the overall dissipation characteristics of the wavefield? • Are there significant interactions between short waves and transient long waves?

  4. Experiments • One year project from NEES program, National Science Foundation • Use NEES Tsunami facility at Oregon State University • Tsunami Wave Basin: • 48.8m x 26.5m x 2.1m • 29-paddle multi-directional piston wavemaker • 4 resistance gages and 2 ADVs on movable bridge

  5. Experiments Tsunami “height” ~30 cm Water depth 0.75 m Different runs with tsunami either at middle or end of swell

  6. Long Wave Breaking Location Without swell With swell x=25.3m x=25.3m

  7. Breaking Location Maximum free surface elevation

  8. Dissipation Analysis Truncated time series: 2048 points

  9. Dissipation Analysis Eddy viscosity breaking mechanism of Zelt (1991) (altered to operate on ) From Kaihatu and Kirby (1996) where: Breaking Parameter (B.P.) - Solitary Wave Breaking!

  10. Dissipation Analysis *: slope of log ; o: neg. slope of log S(f) Linear shoaling and dissipation Random wave Bowen and Kirby Case A Random wave Bowen and Kirby Case B n ~f 2 Random wave Bowen and Kirby Case C From Kaihatu et al. (2007 JGR)

  11. Dissipation Analysis fp 0.5f(Nyq) fp 0.5f(Nyq) Kaihatu et al. (2007)

  12. Dissipation Analysis

  13. Dissipation Analysis B.P.=0.3 (Zelt 1991)

  14. Dissipation Analysis • Wavelet Transforms • Average spectra over time of tsunami • Calculate disspation quantities using averaged spectrum Swell 1 m=2 S(f) Tsunami-Swell 1 m=2 α(f) Time Series of  Tsunami-Swell 4 Swell 4 m=2 m=2 Spectra from Wavelet Transform

  15. Dissipation Analysis B.P.=0.9 (Goertz et al., this conference)

  16. Wavelet Bicoherence Wavelet bicoherence analysis using Dong et al. (2008) Swell 1 h=0.1m Tsunami and Swell 1 h=0.1m Thanks to Dr. Yuxiang Ma, Dalian Univ., for the analysis code

  17. Conclusions Experiments on short wave interaction with a long transient wave performed. Dissipation characteristics of overall wavefield deduced using an assumed eddy viscosity breaking model. Spectral characteristics of dissipation of long wave – short wave combined signal are similar to that of short wave signal only. Energy flux estimates comparable between swell-alone and combined cases. Wavelet transforms offer different interpretation. Wave breaking parameter changes swell dissipation estimates. Wavelet bicoherence offers close examination of interactions.

  18. Future Work • Make further use of transient analyses • Wavelet transforms • Wavelet bicoherence (Dong et al. 2008) • Hilbert-Huang transforms (Huang et al. 1998)

  19. Phase Speed Analysis Long wave breaking

  20. Dissipation Analysis S A1 Dissipation Coefficient Deduced from Wave Group Experiment of van Noorloos (2003) n f h=0.2857m h=0.2429m h=0.1571m S n A3 h=0.0714m h=0.0286m h=0.0029m Dissipation coefficient n Kaihatu and El Safty 2011 (2010 ICCE) f

  21. Dissipation Analysis Tsunami alone vs. Tsunami / Swell Swell alone vs. Tsunami / Swell 1 2 3 4 Dissipation Intensity = Total Dissipation / Length of time series

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