Numerical modelling of wind-induced circulation in the Gulf of Thermaikos using a non-orthogonal boundary-fitted coordinate system

Boundary-fitted coordinate systems are becoming increasingly popular in computational hydrodynamics since they allow an accurate representation of curved flow boundaries. This paper presents details of a two-dimensional, depth-averaged numerical model which utilises a non-orthogonal coordinate transformation to solve the shallow water equations. The model has been designed to predict wind-induced circulation patterns in semi-enclosed coastal seas of irregular shape. The scheme consists essentially of two modules: the first generates the non-orthogonal grid within the prescribed flow domain using an elliptic grid generation technique, whilst the second solves the transformed non-linear shallow water equations in a stable and nondiffusive manner. The curvilinear approach provides an accurate representation of the complex shape of natural flow domains and avoids the approximate 'staircase' perimeter which occurs in Cartesian finite-difference methods. The versatility of the model is demonstrated by simulating the wind-induced circulation patterns in the Gulf of Thermaikos, a semi-enclosed bay close to the City of Thessaloniki in Northern Greece.