On the automatic and a priori design of unstructured mesh resolution for coastal ocean circulation models

Abstract

This study investigates the design of unstructured mesh resolution and its impact on the modeling of barotropic tides along the United States East Coast and Gulf Coast (ECGC). A discrete representation of a computational ocean domain (mesh design) is necessary due to finite computational resources and an incomplete knowledge of the physical system (e.g., shoreline and seabed topography). The selection of mesh resolution impacts both the numerical truncation error and the approximation of the system’s physical domain. To increase confidence in the design of high-resolution coastal ocean meshes and to quantify the efficacy of current mesh design practices, an automated mesh generation approach is applied to objectively control resolution placement based on a priori information such as shoreline geometry and seabed topographic features. The simulated harmonic tidal elevations for each mesh design are compared to that of a reference solution, computed on a 10.8 million vertex mesh of the ECGC region with a minimum shoreline resolution of 50 m. Our key findings indicate that existing mesh designs that use uniform resolution along the shoreline and slowly varying resolution sizes on the continental shelf inefficiently discretize the computational domain. Instead, a targeted approach that places fine resolution in narrow geometric features, along steep topographic gradients, and along pronounced submerged estuarine channels, while aggressively relaxing resolution elsewhere, leads to a mesh with an order of magnitude fewer vertices than the reference solution with comparable accuracy (within 3% harmonic elevation amplitudes in 99% of the domain).