Initializing the Level Set Function
If the study type Transient with Phase Initialization is used in the model, the level set variable is first initialized so that it varies smoothly between zero and one over the interface. For that study, two study steps are created, Phase Initialization and Time Dependent. The Phase Initialization step solves for the distance to the initial interface, Dwi. The Time Dependent step then uses the initial condition for the level set function according to the following expression:
in domains initially outside the interface and
in domains initially inside the interface. Here, inside refers to domains where ϕ < 0.5 and outside refers to domains where ϕ > 0.5.
If the Transient with Phase Initialization () study is being used, then, for the initialization to work, it is crucial that there are two Initial Values nodes. One of the Initial Values nodes should use Specify phase: Fluid 1 (ϕ = 0) and the other Specify phase: Fluid 2 (ϕ = 1). The initial fluid-fluid interface is then automatically placed on all interior boundaries between both phases. The smooth initialization is not used in domains with User defined initial values.
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The Level Set Interface
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Studies and Solvers and Time Dependent with Initialization in the COMSOL Multiphysics Reference Manual