For twenty years, the integrated modelling system WOLF has been entirely self-developed by the research group HECE. It integrates the results of more than a dozen PhD thesis.

The model enables the simulation of the whole range of flow and transport processes of relevance for research and real-world applications in civil and environmental engineering. Including a physically-based hydrological model as well as 1D, 2D-horizontal, 2D-vertical and 3D hydraulic models, WOLF constitutes a unique tool for rainfall-runoff modelling, flood risk analysis, design of hydraulic structures, sediment transport analysis and morphodynamic modelling, as well as modelling of air entrainment and contaminant transport by surface flow.

A unified mathematical description of free surface and pressurized flow is used, both in 1D and 2D. The complex turbulent flow involved in these processes are modelled by means of standard and advanced formulations of the Reynolds-Averaged Navier-Stokes equations, as well as depth- and cross-sectional averaged forms of these equations. A two-length scale k-e turbulence model is used to account explicitly for the anisotropic turbulent mixing induced by the lateral shear and by the bottom-generated turbulence. Additional equations reproduce sediment movement with bedload and suspended load transport, together with the resulting erosion and deposition processes.

The modelling system also includes an optimization tool based on genetic algorithms, which enables automatic model calibration or the optimal geometric design of hydraulic structures.

A consistent numerical approach is applied to discretize the different models throughout the whole spectrum of considered scales, from the pipe level up to the reach and catchment levels. It consists in a finite volume approach based mostly on structured multiblock grids. An original flux vector splitting guarantees the stability, accuracy and efficiency of the computations, even under highly transient flow and transport conditions. As required, suitable techniques, such as the levelset approach, are used to track moving interfaces. To accommodate the broad spectrum of time scales involved in sediment transport modelling, the modelling system enables different levels of coupling between the flow submodel and the submodels for sediment transport and morphodynamic updates.

The computational core is coded in object-oriented Fortran 2008. The model offers a user interface enabling GIS-type operations for processing of input and output data. Currently, a major effort is made to enable parallel computing on single machine (OpenMP) and cluster (MPI, CoArray), and to integrate some key graphical cross-platform open source libraries (GTK+, GNUPlot, GDAL).

Widely recognized nationally and internationally, WOLF is routinely exploited for research, education and consultancy. It was verified against many experimental and other reference test cases. It has been used now in over 30 international peer-reviewed journal publications and within several national and European research projects. WOLF was selected by the regional authorities in Belgium to perform all detailed 2D flow simulations to support official inundation mapping, including in the framework of the European Floods Directive. It has been recognized as one of the very few models suitable to conduct fully coupled computations of highly erosive flows such as induced by dam breaching or dam break in natural erodible valleys. It has also been used in different engineering companies (e.g., in Switzerland) as well as in other European Universities (e.g., Politecnico di Milano).

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