in principle, you could also use a moisture source to simulate the uptake of ground water. But I think using the capillary absorption mechanism through the surface (which is normally used to determine the absorption of rain water through the wetted surface) is more appropriate.
If you model the capillary absorption of ground water as "rain" absorption, the absorbed water enters the component through the surface, as does the ground water. If you put a moisture source into the component, you have a more or less extended region within the component which releases moisture. Of course, if the exact location where the moisture appears is not important for your simulation, both alternatives are possible.
I'm attaching a simple weather file you can use to model capillary absorption from a practically unlimited water supply (the attached file had to be zipped because for some reason the forum software does not allow the file extension *.WAC).
The file consists of one single line. When WUFI reaches the end of a weather file (in this case, after each one-hour step), it jumps back and starts reading the file again fom the beginning. The geographical coordinates and the height are not needed and have been set to a number which signals 'unspecified'.
The temperature has been set to 20 °C. You may set this to the ground temperature of your case. If you need a variable ground temperature, you must create a file like this, but with an appropriate number of lines (one for each hour. Don't forget to adjust the "Number of DataLines" parameter in the header accordingly).
The relative humidity has been set to 100 % ( = 1) and should be left at this value.
The rain has been set to a large number (1000). This number would not be realistic as a real rain rate, but the purpose here is to provide more water than the component can absorb, depending on its capillary properties and current water content. This ensures that the absorptive capacity of the component is the limiting factor for the water uptake, not the amount of water available for absorption. The parameter "adhering fraction of rain" for the relevant surface should be set to 1 to avoid limiting the amount of available water.
The rain column has been tagged as a "RM" column (= rain, measured) instead of the "RN" (= normal rain) which is usually used for rain in weather files. Usually, the rain hitting the component surface is the driving rain, while the rain data provided by meteorological stations describe the "normal" rain measured on a horizontal surface. WUFI usually feeds the RN data and the wind data to a driving rain model which estimates the resulting amount of driving rain and then offers this to the component for capillary absorption. In this case, however, no wind data exist and the driving rain model would fail. The column tag "RM" (instead of the usual "RN") tells WUFI that these data should be used as given, and should not be run through the driving rain model (they are supposed to be the measured driving rain, requiring no further modification by a driving rain model).
Water which is not absorbed simply "runs off" and is not considered further in the simulation, so for the present purpose we may choose an arbitrarily large number without compromising the simulation result.
10 Line Offset to 'Number of Data Columns'
Climate file for free capillary water absorption
-1e11 Longitude [°]; East is positive
-1e11 Latitude [°]; North is positive
-1e11 HeightAMSL [m]
1.0 Time Zone [h from UTC]; East is positive
1 Time Step [h]
1 Number of DataLines
3 Number of DataColumns
TA HREL RM
20 1.0 1000
In addition to the uptake of ground water, this file could also be used to simulate a water absorption experiment. In such an experiment, one face of a material specimen is submerged in water so that its capillary forces can absorb water from this unlimited supply, the absorbed amount depending on the capillary properties and the current water content. The amount of water which an initially dry specimen absorbs per square meter of wetted area and per square-root of absorbing time is the water absorption coefficient or A-value [kg/(m^2h^0.5)]. By simulating such an experiment you can determine the A-value corresponding to the set of liquid transport coefficients of the material. (I'm adding this note so that I can simply refer to this posting if a question about simulating water absorption experiments comes up.)