  The smoothed particle hydrodynamics (SPH) method has been increasingly used
to study fluid problems in recent years; but its computational cost can be high
if high resolution is required. In this study, an adaptive resolution method
based on SPH is developed for multiphase flow simulation. The numerical SPH
particles are refined or coarsened as needed, depending on the distance to the
interface. In developing the criteria, reference particle spacing is defined
for each particle, and it changes dynamically with the location of the
interface. A variable smoothing length is used together with adaptive
resolution. An improved algorithm for calculating the variable smoothing length
is further developed to reduce numerical errors. The proposed adaptive
resolution method is validated by five examples involving liquid drops impact
on dry or wet surfaces, water entry of a cylinder and dam break flow, with the
consideration of ambient gas. Different resolution levels are used in the
simulations. Numerical validations have proven that the present adaptive
resolution method can accurately capture the dynamics of liquid-gas interface
with low computational costs. The present adaptive method can be incorporated
into other SPH-based methods for efficient fluid dynamics simulation.
