TUFLOW General Discussion

Frequently Asked Questions (FAQ)

Why seemingly identical models can produce non-identical results?

Generally speaking single path numerical solvers such as those used for hydraulic modelling should be able to produce the same numerical results twice to the last bit of every binary number calculated and output. However, this can become difficult with parallel computations as the order in which a list of single or double precision numbers are summated can produce slightly different rounding errors and thereby produce very slightly different results. For the vast majority of models TUFLOW Classic, TUFLOW HPC and TUFLOW FV will reproduce numerically identical results when run on the same CPU/GPU. Occasionally this might not be the case when identical simulations are run on different CPUs/GPUs due to hardware differences.
Prior to 2020-10-AB release, the new boundary method introduced in TUFLOW HPC 2020-01-AA release for inflowing HT and QT boundaries (refer see Section 6.1 of the 2020 Release Notes) can in rare situations be affected by bitwise reproducibility when parallelised. When this issue occurs, very slight numerical differences can occur throughout the model, noting that they will be of a much smaller magnitude than those that occur when carrying out impact assessments, but will cause undesirable numerical noise in the impact mapping.

Do I need TUFLOW licence to create TUFLOW inputs and view results from TUFLOW models?

No, a TUFLOW licence is only needed to run simulations. All TUFLOW inputs and outputs use free open formats that are read and editable by third party software, for example QGIS and Notepad++:

• Download Notepad++ to create and review tabular data: Notepad++ installation and tips.
• Download QGIS: QGIS installation and tips.
• To review maximum ASC/FLT grids just drag and drop them into QGIS.
• Install the TUFLOW Plugin: TUFLOW QGIS plugin installation and tips.
• Use TUFLOW Viewer to review XMDF results: TUFLOW Viewer.

How closely would TUFLOW results match other hydraulic software?

Different software will give different results for the simple reason that they all include different calculation assumptions. Understanding what those assumptions are and how they influence results will be important for the sensitivity testing. TUFLOW, like all hydraulic modelling software, needs to be applied appropriately and models should be calibrated to real world events if calibration data are available.

Can TUFLOW's 1D engine be used for modelling complex pipe hydraulics?

TUFLOW can model complex pipe hydraulics with a level of accuracy similar or better than industry peers. There are a few notable features that place TUFLOW ahead of other software:

• TUFLOW's 1D solution accurately accounts for both non-pressurised and pressurised flows within the pipe network.
• TUFLOW's treatment of pipe junction losses is one of the most sophisticated. The default method (Engelund) will adjust losses dynamically every timestep of the simulation based on the hydraulic conditions at that time and the following:
  • changes in pipe size
  • expansion/contraction if there is a manhole at the pipe junction
  • variation in pipe approach and exit angles at junctions
  • variation in pipe approach and exit elevation at junctions
• Alternative loss methods to Engelund are also available, such as Fixed losses. The Fixed method conforms with some industry guidelines, such as the Qld Urban Drainage Manual (QUDM). Fixed losses are not set as the default as this generally requires the modeller to manually enter appropriate values at every manhole, whereas the Engelund approach in TUFLOW, which is based on that in MIKE Urban with several improvements developed in conjunction with Gold Coast City Council’s infrastructure team, provides an excellent automatic approach with no or minimal user input beyond the pipe and manhole geometry. The other advantage of the Engelund approach is that it is dynamic and adjusts losses according to the flow conditions, whereas the Fixed approach assumes the same energy loss coefficient for all flow regimes. TUFLOW also allows having a mix of different methods in the one model, for example, there may be a special manhole where the Fixed or other approach needs to be applied.
• There are numerous pit inlet options, from automatic capture rates to manually defined depth-discharge relationships. In all cases the 2D cell water depth at the inlet influences the amount of flow entering the pit, and as such the 1D underground pipe network.
• The 2020 TUFLOW release offers sub-grid topography sampling to process all elevations within the cell into a depth/volume relationship for its calculations. This approach ensures much more accurate water depth estimations at pit inlets, even if the 2D cell resolution is much larger than the geometry of the drain at the inlet. This in turn translates to more accurate representation of the pit inflow, and as such flow through the entire pipe network. No other 1D/2D stormwater drainage modelling software offers this functionality. The new Quadtree functionality also allows the user to model key flowpaths, such as road drains, in high resolution.
• The 2D overland approach used by TUFLOW ensures any above ground inundation is defined by the model topography. This approach avoids any engineering judgement flow path definition mistakes which the 1D overland software suffer from.

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