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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 , John Goertz , Ying-Po Liao, Richard Irwin and Deirdre Devery Coastal and Ocean Engineering division Zachry Department of Civil engineering Texas a&m university

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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, John Goertz, Ying-Po Liao, Richard Irwin and Deirdre Devery 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 Phase speed analysis Conclusions

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

  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:

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

  11. 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)

  12. 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

  13. Dissipation Analysis fp 0.5f(Nyq) fp 0.5f(Nyq)

  14. Dissipation Analysis

  15. Phase Speed Analysis Long wave breaking

  16. Conclusions and Future Work • Experiments on short wave interaction with a long transient wave performed • Dissipation characteristics of overall wavefield deduced using an assumed eddy viscosity breaking model • Dissipation “intensity” highest for long wave in isolation, and lowest for short wave in isolation • Spectral characteristics of dissipation of long wave – short wave combined signal are similar to that of short wave signal only • Unlike wave group signals • Breaking process has effect on phase speed estimates

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