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Journal ArticleDOI

Performance comparison of spectral wave models based on different governing equations including wave breaking

08 Mar 2009-Ksce Journal of Civil Engineering (Korean Society of Civil Engineers)-Vol. 13, Iss: 2, pp 75-84
TL;DR: The performance of three spectral wave models based on different types of governing equations, as discussed by the authors/DIF S, MIKE 21 BW module, and SWAN, was compared by using four laboratory or field experimental data sets as discussed by the authors.
Abstract: The performance of three spectral wave models based on different types of governing equations, REF/DIF S, MIKE 21 BW module, and SWAN, was compared by using four laboratory or field experimental data sets. The comparison was focused on accurate prediction of measured wave heights. Characteristics of the three wave models were discussed and their overall predictability of the measured data was evaluated by calculating mean absolute relative errors of wave height. All the numerical models simulated fairly well shoaling and breaking of waves propagating on a plane sloping beach, but the model accuracy was somewhat degenerated in simulating waves propagating over a barred beach. Among the three models, MIKE 21 BW was the most insensitive to the bathymetric change. Combined refraction-diffraction over a shoal without breaking was quite well simulated by the models, especially by REF/DIF S and MIKE 21 BW. When waves break over the shoal, however, all the models failed to reproduce the wave field behind the shoal. The agreement with data in simulating wave diffraction around breakwater was remarkably good for MIKE 21 BW, but poor for other two models. Except the last simulation, the mean absolute relative errors of wave height from the three models ranged between 3 and 27%.

Summary (2 min read)

1. Introduction

  • Accurate modeling of random wave propagation over an uneven bathymetry is an essential prerequisite for design of coastal structures and prediction of nearshore currents and sediment transport.
  • For numerical models of the mild slope equation using finite difference scheme, a comparative study has been carried out by Maa et al. (2000).
  • To the knowledge of the authors, there is no study comparing simulation results of the spectral wave models based on different governing equations including the effects of wave breaking, which is the main interest of the present study.
  • The performance of these models was examined by comparing their calculation with four well-documented data sets obtained from laboratory experiments or field measurements (Vincent and Briggs, 1989; Mase and Kirby, 1992; Briggs et al., 1995; Birkemeier et al. 1997).
  • Since most of the data sets provide only wave height data, the major focus of the comparison was placed on this physical quantity.

2.1 REF/DIF S

  • S is a weakly nonlinear combined refraction and diffraction model developed by Kirby and Özkan (1994).
  • In REF/DIF S, individual wave components of a given frequency and direction are simultaneously propagated through the computing domain and the statistical wave parameters are calculated after each forward spatial step.
  • Accurate results are restricted to waves propagating on a mild bottom slope within 45 from the mean wave direction.
  • MIKE 21 BW can simulate the combined effects of almost all wave phenomena occurring in nearshore regions, including wave grouping, surf-beats, and triad wave interactions (DHI Software, 2004).
  • The 2DH (two horizontal dimensions) module was used.

2.3 SWAN

  • SWAN is a phase-averaged wave model that computes random, short-crested wind-generated waves in coastal regions and inland waters (The SWAN team, 2007).
  • The model is based on the wave action balance equation with various sources and sinks that accounts for generation, dissipation, and wave–wave interactions of waves in deep and shallow waters (Booij et al., 1999).
  • In SWAN, wave diffraction, which is not explained by the original wave action balance equation, is modeled by a phase-decoupled refraction–diffraction approximation (Holthuijsen et al., 2003).
  • This enables its application to the simulation of wave transformation in coastal areas where wave reflection and diffraction are significant, such as wave field around coastal structures.
  • In Table 1, the main features of the above three spectral wave models are summarized.

3. Comparison of the Numerical Simulation Results

  • 1 Shoaling and breaking over constant slope 3.1.1 Experimental Data Mase and Kirby (1992) conducted experiments in a wave flume of 47 cm water depth.
  • Among a total of 17 experimental conditions, two cases (N4 and B5) shown in Table 2 were selected for the present numerical simulation.
  • In Figure 6, the SWAN result without wave diffraction (Diff off) was also provided to show the effect of wave diffraction in the model.
  • It seems that the simulated wave heights outside the surf zone were also somewhat higher than the observation, which might result in the disagreement of wave height due to wave shoaling.

Refraction Yes Yes Yes

  • Sketch of the experimental setup (Mase and Kirby, 1992).
  • Normalized wave heights along the transect measured from the experiment (Vincent and Briggs, 1989) and computed by the three models (Case N4).
  • Significant wave heights of the DELILAH field measurement and computational results by the three models (Case D1).

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Editorial Manager(tm) for KSCE Journal of Civil Engineering
Manuscript Draft
Manuscript Number:
Title: Performance Comparison of Spectral Wave Models Based on Different Governing Equations
Including Wave Breaking
Article Type: Research Paper
Corresponding Author: Dr. Sang-Ho Oh, Ph.D
Corresponding Author's Institution: Korea Ocean Research & Development Institute
First Author: Sang-Ho Oh, Ph.D
Order of Authors: Sang-Ho Oh, Ph.D; Kyung-Duck Suh, Ph.D; Sang Young Son; Dong Young Lee,
Ph.D
Abstract: The performance of three spectral wave models based on different types of governing
equations, REF/DIF S, MIKE 21 BW module, and SWAN, was compared by using four laboratory
or field experimental data sets. The comparison was focused on accurate prediction of measured
wave heights. Characteristics of the three wave models were discussed and their overall
predictability of the measured data was evaluated by calculating mean absolute relative errors of
wave height. All the numerical models simulated fairly well shoaling and breaking of waves
propagating on a plane sloping beach, but the model accuracy was somewhat degenerated in
simulating waves propagating over a barred beach. Among the three models, MIKE 21 BW was the
most insensitive to the bathymetric change. Combined refraction-diffraction over a shoal without
breaking was quite well simulated by the models, especially by REF/DIF S and MIKE 21 BW. When
waves break over the shoal, however, all the models failed to reproduce the wave field behind the
shoal. The agreement with data in simulating wave diffraction around breakwater was remarkably
good for MIKE 21 BW, but poor for other two models. Except the last simulation, the mean absolute
relative errors of wave height from the three models ranged between 3 and 27%.

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Coastal & Harbor Engineering
Performance Comparison of Spectral Wave Models Based on
Different Governing Equations Including Wave Breaking
Sang-Ho Oh
a*
, Kyung-Duck Suh
b
, Sang Young Son
c
, Dong Young Lee
d
a
Coastal Engineering & Ocean Energy Research Department, Korea Ocean
Research and Development Institute, Ansan 426-744, Korea,
ohsangho@kordi.re.kr
Tel: +82-31-400-7802, Fax: +82-31-408-5823
b
Department of Civil and Environmental Engineering & Engineering Research
Institute, Seoul National University, Seoul 151-744, Korea, kdsuh@snu.ac.kr
c
Hyundai Institute of Construction and Technology, Hyundai Engineering &
Construction Company, Yongin 449-761, Korea, syson@hdec.co.kr
d
Climate Change & Coastal Disaster Research Department, Korea Ocean
Research and Development Institute, Ansan 426-744, Korea, dylee@kordi.re.kr
Manuscript
Click here to download Manuscript: KSCE-JCE manuscript.doc

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ABSTRACT
The performance of three spectral wave models based on different types of
governing equations, REF/DIF S, MIKE 21 BW module, and SWAN, was
compared by using four laboratory or field experimental data sets. The
comparison was focused on accurate prediction of measured wave heights.
Characteristics of the three wave models were discussed and their overall
predictability of the measured data was evaluated by calculating mean absolute
relative errors of wave height. All the numerical models simulated fairly well
shoaling and breaking of waves propagating on a plane sloping beach, but the
model accuracy was somewhat degenerated in simulating waves propagating over
a barred beach. Among the three models, MIKE 21 BW was the most insensitive
to the bathymetric change. Combined refraction-diffraction over a shoal without
breaking was quite well simulated by the models, especially by REF/DIF S and
MIKE 21 BW. When waves break over the shoal, however, all the models failed
to reproduce the wave field behind the shoal. The agreement with data in
simulating wave diffraction around breakwater was remarkably good for MIKE
21 BW, but poor for other two models. Except the last simulation, the mean
absolute relative errors of wave height from the three models ranged between 3
and 27%.
Keywords: spectral wave model, model comparison, irregular waves, wave
breaking, refraction-diffraction

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3
1. Introduction
Accurate modeling of random wave propagation over an uneven bathymetry is
an essential prerequisite for design of coastal structures and prediction of
nearshore currents and sediment transport. During the last few decades, a number
of spectral wave models have been developed to improve the modeling accuracy
and a great progress has been made until recently. Most spectral wave
transformation models are classified into three categories depending on the
governing equations that are employed: the mild slope equation, Boussinesq
equation, and the wave action balance equation. Although the theoretical
background and target range of application of these governing equations are much
different, many wave models based on these equations have been widely applied
to resolving practical problems of wave propagation in the coastal zone.
Several researches have been carried out to compare the performance of
different wave models. For numerical models of the mild slope equation using
finite difference scheme, a comparative study has been carried out by Maa et al.
(2000). In their study, the effects of shoaling, refraction, and diffraction of six
regular wave transformation models were analyzed, while energy dissipation due
to wave breaking was not considered. Lin and Demirbilek (2005) compared the
overall performance of two spectral wave models solving the wave action balance
equation with an idealized inlet data. However, to the knowledge of the authors,
there is no study comparing simulation results of the spectral wave models based
on different governing equations including the effects of wave breaking, which is
the main interest of the present study.

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Q1. What have the authors contributed in "Editorial manager(tm) for ksce journal of civil engineering manuscript draft manuscript number: title: performance comparison of spectral wave models based on different governing equations" ?

The performance of three spectral wave models based on different types of governing equations, this paper/DIF S, MIKE 21 BW module, and SWAN, was compared by using four laboratory or field experimental data sets this paper.