Saturation and hysteresis

Saturation and hysteresis
SPRING-help >> Description oft he data types >> Material data and geometry specifications >>

Attributes:

ASAT [-] (element wise) (initial saturation),

USAT [-] (element wise) (Values for Van-Genuchten-parameter, only vertical and 3D models)

 

For flow calculation with the SITRA module, three different parameter sets are provided for the residual saturation (Sres), the reciprocal value of the water inlet pressure (a = 1/pe), the pore size distribution index (n) and the specific parameters in the relative K-value calculation (l). Depending on the sediment type (sand, silt or clay, which is determined by the order of magnitude of the corresponding K-value), the following parameters are used in the pressure/saturation function and in the function for the relative K-value:

 

K-value [m/s]

Sres

a

n

l

Soil type

> 9.81*10-4

0.2

1.4*10-3

1.5

0.5

Sand

9.81*10-4 bis 9.81*10-7

0.4

2.5*10-4

1.35

0.5

Silt

< 9.81*10-7

0.9

1.25*10-4

1.3

0.5

Clay

 

For numerical stability, the relative K-values calculated from these functions have a lower limit of 1.0*10-2 m/s.

If values other than the predefined classes above are to be used, the definition must be made via soil areas (element areas). The USAT attribute is then used to assign the desired parameter value combinations and a corresponding zone identification number to each element in that area. Each of these zone identification numbers will then have a unique set of associated van Genuchten parameters. USAT must be fully defined. Once the USAT parameter has been defined, the parameters can be modified interactively in SPRING via: Attributes Extras van Genuchten parameters in the following dialog box:

 


Input of newly defined van Genuchten parameters

The parameters are saved in the model file in the following format:

Van Genuchten Parameter:

1 0.400000 0.000250 1.350000 0.010000 0.500000 1.000000

Hysteresis-Parameter:

1 0.400000 0.000250 1.350000 0.010000 0.000000 1.000000

The subsequent assignment of the USAT attribute for 3D models is carried out automatically in the model checking module.

The initial saturation (ASAT) can be defined for each element if flow and transport calculations in unsaturated conditions is required. Then at the start of the simulation, the calculation of the initial pressure potential is performed by using the specified initial saturation values. ASAT must be completely defined. The subsequent assignment is then carried out automatically for 3D models in the model checking module.