Zeki Demirbilek

Infragravity Wave Motions and Runup over Shallow Fringing Reefs

This paper presents the results of a combined laboratory and numerical investigation into the role of infragravity motions in the wave runup process over fringing coral reefs. Laboratory experiments were performed with a reef profile typical of fringing reef systems along the southeast coast of Guam. Spectral analysis of the measured time histories of surface elevation over the reef face and flats show significant changes to the wave energy spectrum shoreward of the break point. Most of the wave energy in the incident wave frequency band is dissipated within a few wavelengths of the reef face with the wave motions over the reef flat and shoreline dominated by oscillations at infragravity periods [O(100s) prototype]. The infragravity wave energy is minimum at the reef crest and increases as waves propagate shoreward over the reef flat and also with increasing water level on the reef. The dominant infragravity mode is the first reef oscillation mode with a wavelength approximately equal to four times the wi...

Estimation of extreme wave heights using GEOSAT measurements

Satellite technology has yielded a large database of global ocean wave heights which may be used for engineering applications. However, the sampling protocol used by the satellite leads to some difficulties in making use of these data for practical applications. These difficulties and techniques to estimate extreme wave heights using satellite measurements are discussed. Significant wave heights for a 50-year return period are estimated using GEOSAT measurements for several regions around North America. Techniques described here may be used for estimation of wave heights associated with any specified return interval in regions where buoy data are not readily available.

Simulation of Waves at Duck (North Carolina) Using Two Numerical Models

Two wave transformation models, SWAN and CGWAVE, are used to simulate wave conditions at the Field Research Facility, Duck (North Carolina). The motivation is to examine how well these models reproduce observations and to determine the level of consistency between the two models. Stationary wave conditions pertaining to three different storm-induced bathymetric representations are modelled. It was found that SWAN and CGWAVE reproduced the observed wave behavior to a large extent, but CGWAVE results tended to be somewhat smaller than the SWAN results and the measurements. The differences were attributed to wave-wave interactions and breaking. Otherwise the models showed a high level of consistency. SWAN and CGWAVE were also used to explore other mechanisms reported in recent literature; the results were either consistent with some observations (in the case of the nonlinear mechanisms) or they shed more light on others (in case of the role of the research pier legs).

Recent Capabilities of CMS-Wave: A Coastal Wave Model for Inlets and Navigation Projects

Abstract The Coastal Inlets Research Program (CIRP) of the U.S. Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL) has developed a nearshore spectral wave transformation numerical model to address needs of the U.S. Army Corps of Engineers (USACE) navigation projects. The model is called CMS-Wave and is part of Coastal Modeling System (CMS) for wave estimates in the vicinity of coastal and estuarine navigation channels. It can simulate important wave processes at coastal inlets including wave diffraction, refraction, reflection, wave breaking and dissipation mechanisms, wave-current interaction, and wave generation and growth. This paper describes recent improvements in CMS-Wave that include semi-empirical estimates of wave run-up and overtopping, nonlinear wave-wave interactions, and wave dissipation over muddy bottoms. CMS-Wave may be used with nested grids and variable rectangular cells in a rapid mode to assimilate full-plane wave generation for circulation and sediment transport models. A brief description of these recent capabilities is provided.

Simulation of wave breaking effects in two-dimensional elliptic harbor wave models

A technique is developed for including the effects of dissipation due to wave breaking in two-dimensional elliptic models based on the mild-slope wave equation. This involves exploration of convergence properties pertaining to iteration due to presence of the nonlinear wave breaking parameter in the governing equations as well as new boundary conditions that include wave-breaking effects. Five wave-breaking formulations are examined in conjunction with the resulting model, which is applied to tests involving a sloping beach, a bar-trough bottom configuration, shore-connected and shore-parallel breakwaters on a sloping beach, and two real-world cases. Model results show that three of the formulations, when used within the context of the modeling scheme presented here, provide excellent results compared to data.

Wave Prediction Models For Coastal Engineering Application

Publisher Summary This chapter provides a review of some state-of-the-art nearshore wave models that can be used for practical prediction in engineering studies. The chapter describes modeling philosophy, strengths, and limitations of models based on the steady state energy equation and the steady and unsteady state mass and momentum equations. Coastal engineering projects such as those dealing with wave agitation in harbors, beach protection, maintenance of navigational channels, studies of shoreline evolution, etc. typically require a detailed knowledge of the wave field in the project area. Mathematical models of wave propagation attempt to simulate the various mechanisms that induce the transformation of waves. This chapter reviews some wave models that strive to provide an acceptable mix of simplification, sophistication, and convenience of application from the standpoint of practical engineering. The purpose of this chapter is to briefly describe the overall philosophy, methodology, advantages, difficulties, and some applications of each modeling strategy. The chapter describes two kinds of wave models commonly used for coastal engineering applications: models based on the conservation of energy and models based on the conservation of mass and momentum. Both types of models can, by some rigorous or approximate method, incorporate many of the mechanisms mentioned in this chapter. Concluding remarks address some general difficulties that a practicing engineer is likely to encounter while using numerical wave models.

Numerical study of sandbar migration under wave-undertow interaction

Reliable simulation of onshore-offshore sandbar migration under various wave and current conditions has remained a challenging task over the last three decades because wave-undertow interaction in the surf zone has been neglected in the existing numerical models. This paper presents the development of an improved sandbar migration model using a phase- and depth-resolving modeling approach. This new model includes interactions between waves and undertow and an empirical time-dependent turbulent eddy viscosity formulation that accounts for the phase dependency of turbulence on flowvelocity and acceleration.The authorsdemonstrate through extensive model-data comparisons thattheseenhancementsresultedinsignificantimprovementsinthepredictivecapabilityofthecross-shoresandbarmigrationbeneathmoderate and energetic waves. The comparison showed wave-undertow interaction playing a crucial role in cross-shore sediment transport. Waves increased the undertow-induced suspended-load flux during offshore sandbar migration, and a weak undertow suppressed the wave-induced onshore bed-load transport during onshore sandbar migration. The proposed empirical time-dependent turbulent eddy viscosity significantly improved the prediction of onshore-directed bed-load transport during onshore sandbar migration. DOI: 10.1061/(ASCE)WW.1943- 5460.0000231.

LABORATORY AND NUMERICAL STUDIES OF HYDRODYNAMICS NEAR JETTIES

Numerical and physical modeling studies were performed by the Coastal Inlets Research Program (CIRP) of the U.S. Army Corps of Engineers to investigate the spatial and temporal behavior of waves and wave-induced currents near jetties of an idealized coastal inlet. Hydrodynamics were examined in the vicinity of two extreme types of jetty structure: a highly absorbing jetty (resembling fairly porous rock rubble structure) and a fully reflective jetty (resembling a vertical sheet pile or caisson type breakwater). Laboratory experiments in a Froude scale of 1:50 were conducted with regular and irregular shore-normal (0°) and obliquely incident (20°) unidirectional waves. Current and wave measurements were made on the up-wave side and inside the inlet as well as in the bay, along a number of cross-shore and along-shore transects. Wave directions were measured by a remote-sensing video-camera system and Acoustic Doppler Velocimeters (ADV). Numerical modeling was performed with the Coastal Modeling System (CMS) consisting of a two-dimensional circulation model coupled to a spectral wave model. Calculated current and wave fields from CMS in the area around and between absorbing or reflected jetties were compared to measurements. The highly reflecting jetty created a circulation cell on the up-wave side of the inlet, whereas the absorbing jetty did not.

Field and numerical comparisons of the RIBS floating breakwater

A new concept in floating breakwaters was successfully field-tested offshore Cape Canaveral, FL in May 1999. The Rapidly Installed Breakwater System (RIBS) has a hybrid design of rigid and membrane components, similar to a ‘Venetian blind’, to permit rapid and expedient deployment. The objective of the RIBS is to reduce Sea State 3 (SS3) wave conditions to Sea State 2 for safe vessel operations. This field study was probably one of the most heavily instrumented floating breakwaters ever deployed. Measured wave transmission coefficients and dynamic wave pressures are compared to two different numerical models. This is the first verification of the numerical model WAMIT with field data.

Uncertainties in the Validation of Harbor Wave Models

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.