The hardening and innovative deployment of gauges since Hurricane Katrina (2005) resulted in a wealth of measured data for Gustav. A total of 39 wind wave time histories, 362 water level time histories, and 82 high water marks were available to describe the event. Computational models – including a structured-mesh deepwater wave model (WAM) and a nearshore steady-state wave (STWAVE) model, as well as an unstructured-mesh “simulating waves nearshore” (SWAN) wave model and an advanced circulation (ADCIRC) model – resolve the region with unprecedented levels of detail, with an unstructured mesh spacing of 100-200 m in the wave-breaking zones and 20-50 m in the small-scale channels. Data-assimilated winds were applied using NOAA’s Hurricane Research Division Wind Analysis System (H*Wind) and Interactive Objective Kinematic Analysis (IOKA) procedures. Wave and surge computations from these models are validated comprehensively at the measurement locations ranging from the deep Gulf of Mexico and along the coast to the rivers and floodplains of southern Louisiana and are described and quantified within the context of the evolution of the storm.
Category Archives: SWAN
Seminar: University of Central Florida
Wave Refraction on Coarse Meshes, Part 2
Updated 2012/04/12: This is an old page. It persists on this site for posterity, but the information presented below is no longer up-to-date. When you are done here, then please click forward to this page, which describes how to control refraction errors with limiters on the spectral propagation velocities.
In a previous page on wave refraction, it was shown that mesh resolution plays an important role in how SWAN handles this physical process. If the mesh is resolved coarsely, then SWAN can refract too much energy, resulting in spikes in the wave solution. In our hurricane applications, we have observed spikes in the significant wave heights of 75m or larger, focused at only a few vertices, because the mesh in those regions does not resolve properly a shallow feature.
To address this problem, we added wave refraction as an attribute to the ADCIRC fort.13 file, so that it can be varied spatially. The user can enable refraction in regions with the necessary level of mesh resolution, and disable refraction in regions that are resolved coarsely. We enabled wave refraction along the northern Gulf coastline and within southern Louisiana, and we no longer saw the spikes in the significant wave heights in the regions offshore.
Peak Periods TPS in South Carolina
However, we have learned recently that wave refraction on coarse meshes can be problematic in other ways besides creating spikes in the significant wave heights. For example, in very shallow regions, the dissipation of bottom friction and breaking would limit the significant wave heights to reasonable values, even if wave refraction was a problem. There would not be any spikes in the significant wave heights. But the focusing of wave energy would be apparent in other ways that are more subtle, such as the existence of peak periods with the maximum possible values.
On this page, we examine an instance of this problem with wave refraction on coase meshes. As a specific example, we consider a mesh that was developed for a flood inundation study along the coastline of South Carolina. It should be noted that, although this example mesh does exhibit these problems with wave refraction, the problems are also evident on other meshes and other applications. For example, we have seen similarly problematic peak periods in our hurricane applications in southern Louisiana. As we have noted previously, any wave model would face this problem of how to handle refraction on unstructured meshes.
Origin of the Hurricane Ike Forerunner Surge
Conference: ADCIRC 2011
Conference: SIAM Geosciences 2011
JJ Westerink, JC Dietrich, CN Dawson, S Tanaka. “High Performance Scalable Computations of Hurricane Driven Wind Waves, Storm Surge, and Flow in Integrated Ocean Basin to Shelf to Inland Floodplain Systems.” SIAM Conference on Mathematical and Computational Issues in the Geosciences, Long Beach, California, 21-24 March 2011.