The author presents a method for modeling and simulation of vehicles with liquid sloshing loads. A modular approach with subsystems obtained by functional decomposition is used: the vehicle components are modeled as a multibody system, and the sloshing fluid dynamics is determined from solving nonstationary incompressible Navier-Stokes equations in the presence of free surfaces. The in- and output variables for the liquid subsystem and multibody system are defined, Navier-Stokes equations are discretized by finite volume method, and resulting linear systems of equations are solved by multigrid method. The author determines the location of free liquid surfaces by applying the volume-of-fluid method. Finally, the algorithm presented is used to determine the dynamics of a partially liquid-filled tank vehicle during braking maneuvers.