The mapping technique projects the vertices of the source free surface onto the corresponding target free surface if the surfaces are in contact. The projection is done with the local normal to the boundary. The mapping is applied symmetrically: fluid1 → fluid2 and fluid2 → fluid1. Note that fluid1 and fluid2 may be the same singular fluid, and that the source and the target free surfaces may be a single free surface.
The numerical parameters for the mapping are as follows:
Threshold contact value a vertex is selected for mapping if its local fluid-contact value is above that threshold (for additional information on fluid-contact, see Fluid-Fluid Contact).
Element dilatation used to detect contact (in which element E is located vertex N, see Figure 15.5: Contact Detection) and to determine the distance of penetration of vertex N to target free surface. The value of the parameter should be the same than above (creation of constraints on velocities).
Scaling factor the algorithm for detection/distance of penetration will only search in the neighborhood of the target free surface: this search volume has a thickness proportional to the local size of the faces of the target free surface and the scaling factor allows you to increase this thickness.
Lower bound of mapping if the distance of penetration is smaller than this bound, the position of the vertex is not corrected.
Upper bound of mapping if the distance of penetration is greater than this bound, the current time step is rejected, and Polyflow starts again with a reduced time step. The correction on coordinates will be applied if the distance of penetration is between the two bounds.
As a good practice, you should impose the upper bound equal to 25% of the element size and the lower bound should be set to 0.5 % of the element size.
Fraction of displacement as the mapping is from fluid 1 to fluid 2 and at the same time, from fluid 2 to fluid 1, each vertex to move should only be displaced by the half of the distance of penetration. The default value (1/2) should not be changed.
Enable/Disable correction in X/Y/Z direction allows Polyflow to neglect/take into account for the displacement in a given direction. For example, in a transient simulation of extrusion, as the flow is mainly in a given direction (for example, Z), then the swelling occurs in the {X,Y} directions, you can neglect correction in the Z direction.