Model Integration and Open MI
For coastal sediment systems, different classes of landform and interactions between estuary, coast and inner shelf sub-systems are traditionally handled with different types of model as shown elsewhere on this site. Understanding coupled coastal systems requires integration of these approaches in some way or another. In iCOASST, we focussed on exploring the application of the OpenMI (Open Modeling Interface) Standard (www.openmi.org). It defines an interface that allows models to exchange data in memory at run-time. When this standard is implemented and models are Open MI 'wrapped', they can be run simultaneously and share information, for instance at each time step, making model integration feasible at the operational level. OpenMI is well suited to linking models based on different concepts, with different spatial and temporal resolutions and representations (e.g. 1D, 2D or 3D discretization). This delivers the required aspects of the system framework, model and software integration.
The provision of a robust integrated modelling interface was an essential step towards ensuring that models can be linked and run together. In iCOASST this was provided by the Fluid Earth implementation of the OpenMI standard (Harpham et al., 2014) (http://fluidearth.net/default.aspx). iCOASST coupled both existing and new landform behaviour models developed within the iCOASST project. In the Liverpool Bay composition, two existing models were OpenMI 'wrapped' and coupled to demonstrate the integration process: the UnaLinea one-line model of open coasts and the ASMITA aggregated estuary model (note two UnaLinea model domains were required). In addition, onshore sediment fluxes identified within the POLCOMS simulations of Liverpool Bay where considered as a look-up table. The new models developed within iCOASST are being OpenMI 'wrapped' from their inception. Initially it was proposed that model developers should implement OpenMI independently, but it was found to more efficient to employ an OpenMI expert (in our case John Barnes) to work with each model developer to design and facilitate OpenMI compliance from the beginning. Model development groups are thus free to develop the details of their model with the OpenMI expert facilitating compliance. Building on this, in the Suffolk composition of the Deben estuary and its environs, SCAPE and MESO_i were coupled in OpenMI (note that two SCAPE sections were required). In addition, there was a one-way coupling via the tidal prism of the Deben, which was modelled with ESTEEM. Hence OpenMI was not necessary for this linkage.
OpenMI is not the only approach for model integration. The Coastal Modeling Environment (CoastalME) has been developed within iCOASST. This is a new approach to model coupling and CoastalME aims to identify the commonalities of existing large scale behavioural simulation models and provide a common quantitative framework able to incorporate the different existing conceptual models (i.e. instead of integrating the software models).
Harpham, Q., Cleverley, P., Kelly, D. (2014). "The FluidEarth 2 implementation of OpenMI 2.0". Journal of Hydroinformatics 16, 890-906.