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Hydrodynamic Models

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Hydrodynamic numerical flow calculation is one of the fundamental tasks of all planning and optimisation work in hydraulic engineering which is dealt with at the Department of Hydraulic Engineering in Inland Areas in connection with development and construction and operation and maintenance of federal waterways. The flow calculations are made in the context of model formation with one, two or three-dimensional modelling tools adapted to the relevant issue and provide absolute statements on water levels and flow velocities or relative statements on changes in these flow parameters as a result of planned hydraulic engineering measures. These flow parameters are also the primary input parameters for further considerations in the Department of Hydraulic Engineering in Inland Areas, some of which are the modelling of solid matter transport, ship movement dynamics, the optimisation of chains of impoundments and, recently, also water management issues related to the implementation of the EU Water Framework Directive and matters concerning the restoration of ecological continuity of the bodies of water (§ 34 WHG – German Federal Water Law). Above and beyond this, water levels and flow velocities will be required as important input parameters for the Department of Geotechnical Engineering (ground water modelling and dimensioning of bottom and bank protection) and for the ecological assessment of hydraulic engineering measures carried out by third parties.

One-dimensional Flow Models

One-dimensional numerical flow models with the advantage of fast calculation times are used for the modelling of large-scale river or canal systems. In addition, there are hydraulic questions such as the flood waves propagation, positive and nagative surge caused by lockings, the simulation of weir controls [Gebhardt & Schmitt-Heiderich 2009] or the combined use with navigational dynamics models for the calculation of width and depth requirements for navigation (Heinzelmann et. al 2009). One-dimensional models with the required precision will still be sufficiently effective for use in the future.

The programmes CasCade+ and HEC-RAS are used as standard for the calculation of one-dimensional flows with a free water surface. The BAW’s own method CasCade+ is a further development of the CasCade method of Electricité de France, a 1D HN model for the calculation of non-stationary flow processes. The development of complex (branching) and networked models is just as feasible as the simulation of retention areas. The calculation is based on the discharge equation according to Barré de Saint Venant. The equation is solved through the implicit difference method according to Preissmann [Bleninger et. al. 2006], [Bleninger et. al. 2007]. CasControl is a programme version of CasCade+ that was compiled for MATLAB and is connected via an S-function to Simulink [Rötz 2009].

The River Analysis System (RAS) is part of the new generation of programmes from the Hydrologic Engineering Center (HEC) in the US Army Corps of Engineers. This Windows-based programme for stationary and non-stationary calculation of water levels of branching river systems has a very easy to use user interface and from Version 3.0 onwards also permits a non-stationary calculation of branching waterbody systems. The extension HEC-GeoRAS allows a direct connection to GIS systems. The current HEC-RAS Version 4.0 is available in free of charge through the internet (http://www.hec.usace.army.mil) and includes comprehensive documentation.

FlowMASTER is used for the calculation of one-dimensional pipe flow. FLOWMASTER (http://www.flowmaster.com) is a modular programme for the simulation of 1D flow processes, developed by the company of the same name. It is used to depict stationary and non-stationary flow for incompressible media (fluids) and compressible media (gases). The programme is an important tool for investigating filling and emptying processes at navigation locks, where the opening and closing of the closures in a networked conduit system can lead to complex flow situations. A variety of implemented components and valves and their specific characteristics can be used for the representation and numerical study of a large number of hydraulically linked conduit systems – also, for example, pumping stations.

Multi-dimensional Flow Models

Of the multi-dimensional flow models, two-dimensional, depth-averaged modelling methods at present lead to feasible processing of orders in terms of computer engineering and the time required and are therefore the preferred choice of model. In the long term both two-dimensional, depth-averaged and three-dimensional modelling methods will determine order processing for the field of flow models. While the spatial and temporal extent will in future increase in the use of two-dimensional modelling methods, three-dimensional methods will also increasingly be used; these have a significantly higher forecast precision, especially in the close vicinity of river training structures. In the multi-dimensional field, the Department of Hydraulic Engineering in Inland Areas uses the programmes Telemac2D and Telemac3D, Rismo and UnTrim. All these methods form part of the group of RANS models (Reynolds-averaged Navier-Stokes), but differ with regard to their dimensionality, the numerical methods used and their consideration and realisation of physical processes (turbulence, roughness laws, influence of wind and coriolis force etc.).

The programme system Telemac (http://www.opentelemac.org) is a finite element programme for solving two or three-dimensional flow and transport equations. It has been available in the Department of Hydraulic Engineering in Inland Areas since 1997 and has been used in a number of projects since then. A cooperation agreement was signed with the developer Electricité de France (EDF) in the year 2000. Since then the BAW has had access to all the sources of the method. The adaptation and further development to suit the specialist tasks of the German Federal Waterways and Shipping Administration (WSV) in direct agreement with the EDF is now possible. The long term and continual availability of the code is guaranteed by contract. Both the two-dimensionally depth-averaged programme Telemac2D and the three-dimensional programme Telemac3D can be coupled directly to the morphodynamic programme Sisyphe.

Rismo2D (http://www.hnware.de/rismo/index.html) is a hydrodynamic numerical calculation method for solving depth-averaged shallow water equations according to the finite element method. Rismo 2D was developed at the Institute of Hydraulic Engineering and Water Resources Management (IWW) of the RWTH Aachen University as part of a project of the German Research Foundation (DFG). Since 1996, it has been adapted at the BAW to suit the specialist tasks of the German Federal Waterways and Shipping Administration (WSV). Transport modelling (2D depth-averaged) for conservative or suspended substances can be uncoupled from the flow calculation.

The programme UNTRIM is a two or three-dimensional finite difference method for use in unstructured orthogonal grids. It was developed by Professor Vincenzo Casulli (http://www.portale.unitn.it/dica) of the University of Trento, Italy, and further developed by the BAW to suit its own project work requirements. In its two and three-dimensional form the programme can be coupled with the morphodynamic programme SEDIMORPH.

Bibliography:

  • Bleninger, T.; Fenton, D.F., Jirka, G.H. (2007): Verfahrensbeschreibung des 1-D hydronumerischen Modellsystems CasCade+, Institut für Hydromechanik, Universität Karlsruhe, unveröffentlichter Bericht.
  • Bleninger, T., Fenton, J.D., Zentgraf, R. 2006. One-dimensional unsteady flow modelling for compound channels: case study of a river junction and wide flood-plains of the River Rhine, River Flow 2006, Sept. 6 - 8, 2006, Lisbon, S.1-10.
  • Heinzelmann,C. , Dettmann, T. , Zentgraf, R. 2009, Hydraulisch-fahrdynamische Modelle zur Optimierung der Befahrbarkeit von Binnenwasserstraßen, WasserWirtschaft 4/2009
  • Gebhardt, M.; Schmitt-Heiderich, P. 2008. Entwicklung und Simulation von Regelungsalgorithmen für Staustufen an Bundeswasserstraßen. Wasserwirtschaft, Heft 6/2008, S.16-18.
  • Rötz, A. (2009): Einsatz und Dokumentation einer 1-dimensionalen hydrodynamisch-numerischen Simulationsumgebung am Beispiel der Eder bei Fritzlar. Diplomarbeit am Fachgebiet Wasserbau und Wasserwirtschaft, Universität Kassel.
  • Rouvé,G. & M.Schröder (1994): "Die Entwicklung eines mathematisch-numerischen Verfahrens zur Berechnung naturnaher Fließgewässer"; Abschlussbericht zum DFG-Projekt Ro 365 /31; korr. PDF-Version 12/2004 (http://www.hnware.de/_literatur/ROUVE+SCHROEDER_1994_DFG-Bericht_Ro.365.31.6_korr.Fassung_2004.pdf)


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