• Re: Reference Mass concentration in Density flow-transport model

    Hello Carolina Vera,

    the Reference Mass Concentration or Contaminant mass mean the concentration of the contaminant in the water in ppm. In your case, the concentration of salt, which you will define at the boundaries or for the lower zone in the mass initials. FEFLOW will take these values for the Reference Mass Concentration to calculate the change of the K-value (permeability, conductivity).

    (It is only necessary in cases where the concentration of the contaminant (salt) is high enough to change the viscosity and density of the water sustainable.

    greeting Robert

  • Re: Dispersivity and density-dependent in heterogenous media

    Thank you very much.

    I triangulate my mesh and now i can use the adaptive mesh refinement method. The model is stabilized.
  • Re: seawater intrusion - wedge

    Hello chrisoula,

    a saltwater wedge will de observed when the model runs density-dependent.

    1. Therefore you have to check the set of the global density ratio in FEFLOW. The density ratio is defined as the ratio between the density of the fresh water (min. concentration) and that of the saltwater. As you set the equivalent fresh water hydraulic head, you used the density ratio (depth dependent) already.
    2. To run the model full density-dependent you have to check the specific option setting to incorporate viscosity and the extended Boussinesq approximation.
    3. For the coastline border it is necessary to set a constraint of the mass boundary. For a minimal flux is set to yes and 0 mg/l m3/d. This is necessary for the validation of the set of the constant mass boundary condition at the coastline border. After setting this constraint, the mass boundary condition is only valid if water run into the model.

    To visualize the wedge, you have to check the control output settings in the simulator. Datas could be saved automatically during the simulator runs. Afterwards you can load this data file with the FEFLOW explorer to extract pictures or movies.
  • Dispersivity and density-dependent in heterogenous media

    I try to simulate my tank experiments in FEFLOW 5.015. But i can not simulate the right small dispersion (long. dispersivity 0.01 - 0.0001 and trans. dispersivity 0.001 - 0.00001). I will simulate the hydrodynamically stable case of saltwater (up to 100000 mg/l) underneath de-ionized water (1 mg/l), each half of the tank sized. Always the FEFLOW break down for concentration about 10000 mg/l for heterogenous permeability field. For homogenous permeability field the model works up to highest concentrations and minimal dispersivity.

    The model grid was set up to simulate the x-z cross-sectional geometry and the experimental stochastic realization of the permeability field of the tank. The mesh is 9.8 m in x-direction and 1.225 m in z-direction in a vertical 2D-problem. Each of the, in x 0.2 m and in z 0.025 m sized, 2401 sand blocks (made out of 8 different permeability classes ranging from 1,3e-04 to 2,8e-02 m/s) is represented numerically by 8 horizontally and 4 vertically directed elements, resulting in a total 38907 nodes, respective 38416 quadrilateral elements. The models are run in time until steady-state conditions for the transport, likewise to the experiments, are reached (steady flow - unsteady mass, combined).

    Therefore i have constant head conditions on both sites of the tank for the flow (10 cm = 4 m/d). For the transport i have constant mass at the inflow. Background mass is 1 mg/l. At the outflow there is no mass condition respectively the default free natural boundary. Viscosity incorporated, Bossinesq approximation applied to density coupling extended and the corresponding density ratio was set by me.

    [b]The only warning i get from FEFLOW is the size of the model - only 12.5 square meters.[/b] I try different changes in the solver settings and time step setting of FEFLOW, but nothing helps. How can I stabilize the model at the beginning?

    I hope someone have an idea ... Thank you very much.