========
Overview
========

Cocoa (Coastal and Ocean Circulation on Accelerators) solves the 2D depth-integrated
shallow water equations on unstructured triangular meshes.

Model Capabilities
------------------

Cocoa is designed for simulating:

- **Tidal circulation** in coastal and estuarine environments
- **Storm surge** from tropical and extratropical cyclones
- **Coastal flooding** and inundation
- **Tide-surge interaction** in complex geometries

Physical Processes
------------------

The model includes the following physical processes:

Hydrodynamics
^^^^^^^^^^^^^

- 2D depth-integrated momentum equations
- Generalized Wave Continuity Equation (GWCE)
- Advection and diffusion

Forcing Mechanisms
^^^^^^^^^^^^^^^^^^

- Tidal boundary forcing with multiple constituents
- Astronomical tide potential (direct Moon/Sun computation)
- Atmospheric pressure gradients
- Wind stress (Garratt drag law)

Bottom Friction
^^^^^^^^^^^^^^^

- Quadratic bottom friction
- Variable friction coefficients

Wetting and Drying
^^^^^^^^^^^^^^^^^^

- Element-based wet/dry algorithm
- Maintains mass conservation

Computational Features
----------------------

GPU Acceleration
^^^^^^^^^^^^^^^^

Cocoa leverages Kokkos for GPU acceleration:

- NVIDIA GPUs via CUDA
- AMD GPUs via HIP
- Multi-core CPUs via OpenMP
- Serial execution for debugging

See :doc:`performance` for benchmark results comparing Cocoa with ADCIRC.

Scalable Solvers
^^^^^^^^^^^^^^^^

Linear systems are solved using Trilinos:

- Belos iterative solvers (CG)
- Ifpack2 preconditioners (Jacobi)
- Tpetra linear algebra structures
- Kokkos for performance portability