Clarification on source strength units (kg/(m·s)) in WUFI 2D

[Mir_Hedayat]

Hello,

I am working with moisture sources in WUFI 2D and I would like to clarify the correct interpretation of the unit kg/(m·s) for the source strength.

From the documentation, I understand that WUFI multiplies the specified source strength by a length (not an area) and by the timestep duration to obtain the injected mass.

My question is: when I want to introduce a certain amount of water into one cell (defined by dx × dy), should I calculate the source based on the face length of the cell (dx or dy, depending on orientation), or should I use the full cell area (dx × dy)?

In other words, is the unit “per meter” referring to the third dimension (depth = 1 m in WUFI 2D), or does it refer to one of the face lengths in the 2D plane?

I want to make sure I am converting correctly from kg/m³ (water content) to the source input unit kg/(m·s).

Thank you very much for your clarification!

Best regards,
Mir Hedayat Moosavi

[Christian Bludau]

Hi Mir Hedayat Moosavi,

You have to multiply with dx, as long as your source is not related to a boundary, then it would be the dy for vertical boundaries.

The conversion is as follows, here as an example 100g/m² distributed over three month:
Conversion g -> kg: 100[g]/ 1000[g/kg]= 0.1 [kg]
Time period (t) -> 3600[s/h] * 2180[h] = 7848000 [s]
Source strength: -> 0.1 [kg] / 7848000 [s] = 1.2e-8 [kg/m²s]
Multiply that value with dx [m] to get [kg/ms]
2180h = three months

For WUFI 2d this has to be multiplied with the width of the distribution (see b here: viewtopic.php?p=3166#p3166.

Also see here:
https://wufi.de/en/service/downloads#2d_source_strength

Christian

[Mir_Hedayat]

Hi Christian,
Thank you for your response and the useful information.
Regards,
Hedayat