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TUFLOW General Discussion: Difference between revisions

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***The coupled TUFLOW 1D engine requires the use of the double precision solver to achieve better stability in 1D with more significant numbers. This usually happens with 1D/2D models with ground elevation greater than 100m (TUFLOW 1D engine uses water level as the primary variable as TUFLOW Classic), carved 1D channels within the 2D domain where either the 1D channel itself or the boundary links between 1D and 2D domain can cause the mass error. ***On rare occasions, models with higher elevations and small QT inflow would require double precision, because QT boundaries have hidden 1D node and as such are solved in the TUFLOW 1D engine.
***When the simulation time is long or the model has large Start Time value (more than 100000.0 hours), the around up issue can happen to the simulation time because the model timestep is typically in the order of 0.1~10 seconds. This might cause issues in reading and outputting boundary data.
***When very small inflow or outflows are applied, for example when representing evapotranspiration or the tail ends of storm events.
 
The single precision version of TUFLOW uses significantly less memory (RAM) and is about 20% faster for TUFLOW Classic and four times faster for HPC. Unless required otherwise, the single precision version of TUFLOW is recommended. A good step in the model development is to run the model with both the single and the double precision and if the results / mass balance are similar then the single precision version is sufficient.<br>
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:<font color="blue"><tt>Viscosity Coefficients </tt></font><font color="red"><tt>== </tt></font>k, n, muLow, muHigh, tau0
 
Where k is the viscosity coefficient in Pa.s when ''n'' = 1. Where ''n''=1, this relates to a Newtonian fluid. You can then use an appropriate value for tau0, the stress required to make the fluid move. The Non-Newtonian model uses the Herschel-Bulkley approach which can be used to model Newtonian fluids with different viscosities. See section 5.4 of the <u>[https://downloads.tuflow.com/TUFLOW/Releases/2020-10/TUFLOW%20Release%20Notes.2020-10-AD.pdf 2020 Release Notes]</u> for more information.
 
The graphs below explains the Herschel-Bulkley approach and it’s flexibility:
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:[[File:Formula 004.PNG | 130px]]
 
It should be seen that where Ƭ0''Ƭ<sub>0</sub>=''0, the Herschel-Bulkley equation is the same as the power law model. If ''n'' is 1, then the Herschel-Bulkley equation is the same as the Bingham Plastic model. If Ƭ0''Ƭ<sub>0</sub>''=0 and ''n'' =1, then the Herschel-Bulkley equation is the same as the Newtonian fluid approach. By using the Herschel-Bulkley equation as a Newtonian model, it does allow you to define the viscosity coefficient for the fluid. InThere yourmay casebe you’lla need to convert the viscosity from centiStokes to Pa S (if using an N''n'' value of 1). YouIt canis thenalso possible to define the fluid density using the <font color="blue"><tt>Density of Water</tt></font> command you mention.
 
You can test this out using the following commands.
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:<font color="blue"><tt>Viscosity Coefficients </tt></font><font color="red"><tt>== </tt></font>0.001, 1, 0.0, 1000, 0
 
This uses a ''n'' value of 1, a Ƭ0''Ƭ<sub>0</sub>''=0 and a viscosity coefficient of 0.001 Pa S which is a typical viscosity of water at 20 ℃. This should give comparable outputs to a standard TUFLOW model without the Non-Newtonian functionality.
 
== How closely do TUFLOW results match other hydraulic software? ==
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