  We model a slip boundary condition at fluid-solid interface of an arbitrary
geometry in smoothed particle hydrodynamics and smoothed dissipative particle
dynamics simulations. Under an assumption of linear profile of the tangential
velocity at quasi-steady state near the interface, an arbitrary slip length $b$
can be specified and correspondingly, an artificial velocity for every boundary
particle can be calculated. Therefore, $b$ as an input parameter affects the
calculation of dissipative and random forces near the interface. For $b \to 0$,
the no-slip is recovered while for $b \to \infty$, the free-slip is achieved.
Technically, we devise two different approaches to calculate the artificial
velocity of any boundary particle. The first has a succinct principle and is
competent for simple geometries, while the second is subtle and affordable for
complex geometries. Slip lengths in simulations for both steady and transient
flows coincide with the expected ones. As demonstration, we apply the two
approaches extensively to simulate curvy channel flows, dynamics of an
ellipsoid in pipe flow and flows within complex microvessels, where desired
slip lengths at fluid-solid interfaces are prescribed. The proposed methodology
may apply equally well to other particle methods such as dissipative particle
dynamics and moving particle semi-implicit methods.
