# Delwaq-Scale factor and units in Delwaq - Home - Delft3D

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### Delwaq-Scale factor and units in Delwaq

##### Gholamreza Shiravani, modified 5 Months ago.

#### Delwaq-Scale factor and units in Delwaq

Padawan Posts: 53 Join Date: 6/25/16 Recent PostsHi,

to prepare a Scenario using define Input, we have an Option with the Name of "Dispersion", and here is " Additional vertical Diffusion", I selected the "Use results from hydrodynamics" and "Scale factor" is 1 but model is not converged but for a low scale factor like 1e-006 it is converged. I read the Manual of Delwaq and it was said that this factor is to Change the Units of D-FLOW results in such a way to correspond the Delwaq calculations. However, using IM (inorganic Matterial) it Needs settling velocity as m/d (meter per day) and D-FLOW results are SI, it means the Dispersion unit is m2s-1, velocity ms-1, ... Does Delwaq convert the D-FLOW automatically in m/d or grm-3 (in comparison with kgm-3) or we should apply the Scale factor by Dispersion? To make the Problem undestandable, what means a scale factor for additional vertical Diffusion of 1e-007?

Why for such scale factor Delwaq converges but for higher values, e.g. 1, it does not converge?

When I need a scale factor?

Does scale factor only chanage the Additional vertical Diffusion, which was calculated already through D-FLOW turbulence model (k-Epsilon)?

Why for small scale factors the model convergs?

##### Arjen Markus, modified 5 Months ago.

#### RE: Delwaq-Scale factor and units in Delwaq

Jedi Knight Posts: 235 Join Date: 1/26/11 Recent PostsThere is some misunderstanding here. The scale factor for the vertical dispersion/diffusion is really a scale factor for that parameter only. In the "raw" input you can use scale factors in several locations to facilitate conversion from one unit (the one you find in reports for istance) to another (the one used by the DELWAQ calculation itself). That is what the documentation is referring to or should refer to.

The flow field is read as is and the proper units are m3/s for the flow, m2 for the area and m3 for the volume.

The problem you are facing wrt the stability/convergence has to do with the iteration parameters. The GUI puts in default values, but sometimes you need different ones - try increasing the threshold Tolerance to 1.0e-5 and the maximum number of iterations MaxIter to 1000. This may help the calculation to reach a converged state.