JA M E S KA I H AT U, JO H N G OE RT Z , Y I N G - P O L I A O, R I C H A R D I RW I N A N D D E I R D R E D E V E RY

C O A S TA L A ND OC E A N E N G I NE E R I N G D I V I S I ONZA C H RY D E PA RTM E NT OF C I V I L E N G I NE E R I NG

TE XA S A & M U N I V E R S I TYC O LL E G E S TAT I ON, T X , U S A

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

Outline

Short wave-long wave interactionExperimentsDissipation analysisPhase speed analysisConclusions

Introduction

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

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

Experiments

Test No.

Hs (cm)

Tp (s) kh =a/h Ur

1 5 2 1 0.033 0.0332 5 4 0.45 0.033 0.1633 10 2 1 0.067 0.0674 10 4 0.45 0.067 0.331

Tsunami “height” ~30 cm

Water depth 0.75 m

Different runs with tsunami either at middle or end of swell

Long Wave Breaking Location

With swell

Without swellx=25.3

mx=25.3m

Breaking Location

Maximum free surface elevation

Dissipation Analysis

Truncated time series: 2048 points

Dissipation Analysis

b t th

2b tB h

*1; 2t tB

* *1; 2tt t tB

*0; t tB

From Kaihatu and Kirby (1996)Eddy viscosity

breaking mechanism of Zelt (1991) (altered to operate on )

where:

Dissipation Analysis

Dissipation Intensity = Total Dissipation / Length of time series

Tsunami alone vs. Tsunami / Swell Swell alone vs. Tsunami / Swell

1

2

3

4

Dissipation Analysis

,

2gn x

nx n n ng

CA A A

C

2 21 122 2n gn gn n n

x

g A C C g A

( )1 1( )2n

S fS fg gh f

2

1

( ) Ng

gn n nn

ECD g C A

x

*: 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 waveBowen and Kirby Case B

Random waveBowen and Kirby Case C

Dissipation Analysis

Dissipation coefficient n

n

n

h=0.2857m h=0.2429m h=0.1571m

h=0.0714m h=0.0286m h=0.0029m

Dissipation Coefficient Deduced from Wave Group Experiment of van Noorloos (2003)

Kaihatu and El Safty 2011 (2010 ICCE)

A1

A3

S

S

f

f

Dissipation Analysis

fp fp0.5f(Nyq) 0.5f(Nyq)

Dissipation Analysis

Phase Speed Analysis

maxC g h

Long wave breaking

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