  Particle-based boundary representations are frequently used in Smoothed
Particle Hydrodynamics (SPH) due to their simple integration into fluid
solvers. Commonly, incompressible fluid solvers estimate the current density
and corresponding forces in case the current density exceeds the rest density
to push fluid particles apart. Close to the boundary, the calculation of the
fluid particles' density involves both, neighboring fluid and neighboring
boundary particles, yielding an overestimation of density, and, subsequently,
wrong pressure forces and wrong velocities leading to the disturbed fluid
particles' behavior in the vicinity of the boundary. In this paper, we present
a detailed explanation of this disturbed fluid particle behavior, which is
mainly due to the combined or coupled handling of the fluid-fluid particle and
the fluid-boundary particle interaction. We propose the decoupled handling of
both interaction types, leading to two densities for a given fluid particle,
i.e., fluid-induced density and boundary-induced density. In our approach, we
alternately apply the corresponding fluid-induced and boundary-induced forces
during pressure estimation. This separation avoids force overestimation and
reduces unintended fluid dynamics near the boundary, as well as a consistent
fluid-boundary distance across different fluid amounts and different
particle-based boundary handling methods. We compare our method with two
regular state-of-the-art methods in different experiments and show how our
method handles detailed boundary shapes.
