Journal of Computational Physics 273 (2014) 548–571 Contents lists available at ScienceDirect Journal of Computational Physics www.elsevier.com/locate/jcp An overset grid method for integration of fully 3D fluid dynamics and geophysics fluid dynamics models to simulate multiphysics coastal ocean flows H.S. Tang a,∗ , K. Qu a , X.G. Wu a,b a Department of Civil Engineering, City College, The City University of New York, New York 10031, USA b Zhejiang Institute of Hydraulics and Estuary, Hangzhou, Zhejiang 310020, China a r t i c l e i n f o a b s t r a c t Article history: Received 18 December 2013 Received in revised form 28 March 2014 Accepted 7 May 2014 Available online 23 May 2014 Keywords: Coastal ocean flow Multiphysics Multiscale Fully three dimensional fluid dynamics Geophysical fluid dynamics Hybrid method Domain decomposition SIFOM-FVCOM system It is now becoming important to develop our capabilities to simulate coastal ocean flows involved with distinct physical phenomena occurring at a vast range of spatial and temporal scales. This paper presents a hybrid modeling system for such simulation. The system consists of a fully three dimensional (3D) fluid dynamics model and a geophysical fluid dynamics model, which couple with each other in two-way and march in time simultaneously. Particularly, in the hybrid system, the solver for incompressible flow on overset meshes (SIFOM) resolves fully 3D small-scale local flow phenomena, while the unstructured grid finite volume coastal ocean model (FVCOM) captures large- scale background flows. The integration of the two models are realized via domain decomposition implemented with an overset grid method. Numerical experiments on performance of the system in resolving flow patterns and solution convergence rate show that the SIFOM-FVCOM system works as intended, and its solutions compare reasonably with data obtained with measurements and other computational approaches. Its unparalleled capabilities to predict multiphysics and multiscale phenomena with high- fidelity are demonstrated by three typical applications that are beyond the reach of other currently existing models. It is anticipated that the SIFOM-FVCOM system will serve as a new platform to study many emerging coastal ocean problems.  2014 Elsevier Inc. All rights reserved. 1. Introduction In correspondence with consequence of climate change such as sea-level rise and expansion of human activities along coastlines, it has become urgently needed to study coastal ocean flows involved with multiple types of physical phenomena that intertwine with each other and span a vast range of spatial and temporal scales. For instance, during the Hurricane Katrina in 2005, a number of coastal bridges were damaged by storm surges at scales of bridges, which were driven by surface waves at estuary-scales [1]. The Gulf of Mexico oil spill in the 2010 began as a jet from a port with diameter in O(1) m at the bottom of the ocean and then evolved into floating film patches with horizontal sizes in O(100) miles [2]. In generation of tidal power, for which there is a worldwide resurgence of interest, flows impel turbines at sizes in O(10) m, but they are directly affected by large-scale tidal flows initiated at deep oceans [3]. Multiphysics and multiscale phenomena * Corresponding author. E-mail address: htang@ccny.cuny.edu (H.S. Tang). http://dx.doi.org/10.1016/j.jcp.2014.05.010 0021-9991/ 2014 Elsevier Inc. All rights reserved.