How MOHID Works

MOHID framework consists of 3 main components:

Numerical Tools

This water modelling system is programmed in FORTRAN (ANSI FORTRAN 95) following an object oriented philosophy. Presently there are three core tools:

MOHID Water’s versatility can easily be demonstrated by the range of applications carried out in the last couple of years: applications in the North Atlantic to study general circulation, Oil Spills, eutrophication and residence times in estuaries and reservoirs .

MOHID Land is the most recent core executable of the MOHID Framework and doesn’t have yet the maturity of MOHID Water. So far it was applied to some watersheds, among them the Trancao Basin, which outlet is the Tagus Estuary.

Today the MOHID Water Modelling System is a reliable and robust framework for the upcoming challenges of water modelling. The whole structure of the system is divided into FORTRAN modules, each of them having the functionality of an object class. Actually MOHID model is composed by over 50 modules which complete over 260 000 code lines. Each module is responsible to manage a certain kind of information. The information flux between modules is made in a client/server basis, assuring the information encapsulation in each module. Each module manages his associated memory, which is dynamically allocated.

b MOHID main modules description

MOHID’s modules are structured in a hierarchical way. All executables of the MOHID WaterModelling System are built on the top of one or more base libraries. The hierarchical structure of MOHID’s Framework is presented in next Figure.

Hierarchical design of MOHID Framework

The three core executables files (MOHID Water, MOHID Soil and MOHID Land) can be found at the top of the pyramid. Smaller utility programs are easily built on the top of the libraries, which are usually designed for pre or post-processing results of the core executables.

The common design of all MOHID classes, related to encapsulation/public methods not only turned the code more reliable and protected against errors, but also led to a very well structured code, easily understood by new scientists that work with the model, even taken into account the over 200k code lines which compose MOHID Framework.

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Data Exchange and Storage

Water modeling system MOHID uses 2 components to exchange information between model and graphical user interface:

MOHID’s class EnterData allows to write and read ASCII data files structured in a similar way as XML files. The major reason why this class doesn’t read XML files is that it was implemented just before XML turned popular. It would be quiet easy to modify this class to read XML files, but the backward compatibility with all existing data files would be lost. In order to exchange information between the numerical tools written in FORTRAN 95 and the graphical user interface written in .NET class EnterData has been developed in both languages.

Almost every module which handles any kind of process uses a separate instance of module EnterData, since all modules have to read a specific data file.

HDF (Hierarchical Data Format -> http://hdf.nsca.uiuc.edu) is developed by the National Center for Super Computation Application (NCSA) under the coordination of Mike Folk. MOHID uses HDF to stores the results produced by the model since several years. Actually MOHID uses HDF 5 format in the whole model as new standard.

Several modules of MOHID system use HDF library to store the results, like for instance the modules Hydrodynamic, Waterproperties, Turbulence, etc. Each module produces a separated HDF file. In each of these results files, the underlying grid of the model is stored (which must not be necessarily the same for each module). The grid information contains, besides basic geometry variables (geo-referenced grid connections, bathymetric data, etc.), also information about the type of grid point (water, land inter-tidal).

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User Interfaces

As MOHID Numerical tools become more complex, the need for a well structured graphical user interface grows. With the development of the MOHID Framework a graphical user interface was built in parallel, which allows the model input data, program execution and output results analysis.

MOHID’s graphical user interface is composed by two core programs, written mainly in VB.NET and so it uses full object oriented features:

Both of them incorporate other auxiliar tools to handle MOHID outputs. Some examples of them are:

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