ESTIMATION OF BOUND AND RELEASED INFRAGRAVITY WAVES BASED ON WAVE OBSERVATION AND NUMERICAL SIMULATION IN SHALLOW WATER

Katsuya Hirayama,Yoshiyuki Uno,Hiroaki Kashima

doi:10.9753/icce.v36.currents.37

Abstract

It is mentioned that observed infragravity waves consist of bound waves propagating with short-wave groups, released waves due to reduction of short crest waves and free waves existing in a field. Though it is difficult to distinguish among them, a standard spectrum for infragravity waves is defined by using a relation to a wind wave spectrum. In this study, a comprehensive definition of standard spectrum is newly proposed to estimate infragravity wave heights with the relation between the ratio of wave height and the ursell number of observed wave property, represented by selected data of wave observation in shallow water. Moreover, the release process of bound waves at a harbor entrance is reproduced in numerical simulation using a Boussinesq model for short-wave transformation. These results are verified by comparison to infragravity waves observed at outside/inside of a harbor for a month.

Highlights

It is mentioned that observed infragravity waves consist of bound waves propagating with short-wave groups, released waves due to reduction of short crest waves and free waves existing in a field
Hiraishi et al (1997) has proposed an infragravity wave spectrum related to the Bretschneider-Mitsuyasu (BM in short) spectrum for wind wave by a boundary frequency: fba which is decided by an original parameter; l=fp/fba (Here, fp: peak frequency). l is related to the square root of ratio of infragravity wave energy to total wave energy: RL=(m0L/m0)0.5
It is recognized that the observed HL can be explained by the released wave heights: HLr, those are obtained in the calculations using the Boussinesq model

Summary

Introduction

It is mentioned that observed infragravity waves consist of bound waves propagating with short-wave groups, released waves due to reduction of short crest waves and free waves existing in a field. Hiraishi et al (1997) has proposed an infragravity wave spectrum related to the Bretschneider-Mitsuyasu (BM in short) spectrum for wind wave by a boundary frequency: fba which is decided by an original parameter; l=fp/fba (Here, fp: peak frequency).

Results

Conclusion