Wind wave model
The first numerical model based on the spectral decomposition of the sea state was operated in 1956 by the French Weather Service, and focused on the North Atlantic.
[6] Third generation models explicitly represent all the physics relevant for the development of the sea state in two dimensions.
In the aftermath of World War II, the study of wave growth garnered significant attention.
The global nature of the war, encompassing battles in the Pacific, Atlantic, and Mediterranean seas, necessitated the execution of landing operations on enemy-held coasts.
Consequently, the precise forecasting of weather and wave conditions became essential, prompting the recruitment of meteorologists and oceanographers by the warring nations.
Under the guidance of Harald Svedrup, Walter Munk devised an avant-garde wave calculation methodology for the United States Navy and later refined this approach for the Office of Naval Research.
This pioneering effort led to the creation of the significant wave method, which underwent subsequent refinements and data integrations.
Given that two-dimensional field models had not been formulated during that time, studies were initiated in the Netherlands by Rijkswaterstaat and the Technische Adviescommissie voor de Waterkeringen (TAW - Technical Advisory Committee for Flood Defences) to discern the most appropriate formula to compute wave height at the base of a dike.
However, subsequent studies by Young and Verhagen in 1997 suggested that adjusting certain coefficients enhanced the formula's efficacy in shallow water regions.
A wave model requires as initial conditions information describing the state of the sea.
[6] Wind data are typically provided from a separate atmospheric model from an operational weather forecasting center.
Physics includes wave field refraction, nonlinear resonant interactions, sub-grid representations of unresolved islands, and dynamically updated ice coverage.
Up to 2008, the model was limited to regions outside the surf zone where the waves are not strongly impacted by shallow depths.
[18] The model can incorporate the effects of currents on waves from its early design by Hendrik Tolman in the 1990s, and is now extended for near shore applications.
The model currently comprises 36 frequency bins and 36 propagation directions at an average spatial resolution of 25 km.
Factoring in water depth, wind fetch, and storm duration complicates the equations considerably.
Consequently, for practical applications, nomograms were developed which did away with dimensionless units, instead presenting wave heights in metres, storm duration in hours, and the wind fetch in km.
With a wind speed of 25 m/s from the SSW, the Bretschneider and Wilson formulas suggest an Hs of 3.5 m and a period of roughly 7 s (assuming the storm persists for at least 4 hours).
To address this issue, the SWAN (Simulating WAves Nearshore) program was developed in 1993 by Delft University of Technology, in collaboration with Rijkswaterstaat and the Office of Naval Research in the United States.
SWAN lacks a user interface for easily creating input files and presenting the output.
In many cases, this can yield a sufficiently reliable value for the local wave spectrum, particularly when the wind path crosses shallow areas.
[38] The wave height at the base of the sea dike near Goudorpe on South Beveland, just west of the Westerscheldetunnel, was calculated, with the wind coming from the SW at a speed of 25m/s (force 9 to 10).
In situations where significant refraction occurs, or where the coastline is irregular, the one-dimensional method falls short, necessitating the use of a field model.
This discrepancy arises because the model assumes a broad wave field, which isn't the case for narrow lakes.
[41] A retrospective analysis, or reanalysis, combines all available observations with a physical model to describe the state of a system over a time period of decades.
