# Forcing zones¶

Forcing zones can be used to damp waves near the inlet and outlet to avoid reflections. They work by specifying a zone (a known field), a target result (a known field) and a penalty to be added to the equation system in order to pull the unknown solutiuon towards the known field solution in the forcing zone. See, e.g., 1 and 2 for more details on forcing zones and the selection of penalty parameters.

An example from a wave tank:

forcing_zones:
-   name: outlet velocity damping
type: MomentumForcing
zone: outlet zone/beta
target: waves/u
penalty: 10
plot: no

name

Used for log output and better error messages only

type

One of MomentumForcing or ScalarForcing

variable

If you use ScalarForcing then you must give the name of the variable, e.g. c to force the colour field. For MomentumForcing this defaults to the velocity field u.

penalty

The penalty used to “nunge” the solution towards the target

zone

The name of the known field function that is 1.0 inside the zone and 0.0 outside. The transition is typically smooth. Often a ScalarField is used for this purpose.

target

The name of a known field function that we want to “nunge” our solution towards using the forcing zone.

plot

Show the forcing zone (plots to file). Default off.

Citations

1

R. Perić and M. Abdel-Maksoud. Reliable damping of free-surface waves in numerical simulations. Ship Technology Research, 63(1):1–13, 2016. doi:10.1080/09377255.2015.1119921.

2

Robinson Perić and Moustafa Abdel-Maksoud. Analytical prediction of reflection coefficients for wave absorbing layers in flow simulations of regular free-surface waves. Ocean Engineering, 147:132–147, 2018. doi:10.1016/j.oceaneng.2017.10.009.