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

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 Test No. Hs (cm) Tp (s)kh  =a/h UrUr 15210.033 2540.450.0330.163 310210.067 41040.450.0670.331 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 With swell Without swell x=25.3m

7. Breaking Location Maximum free surface elevation

8. Dissipation Analysis Truncated time series: 2048 points

9. Dissipation Analysis From Kaihatu and Kirby (1996) Eddy viscosity breaking mechanism of Zelt (1991) (altered to operate on  ) where:

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

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

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

13. Dissipation Analysis 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