Analysis of advanced hydraulic engineering problems relies on computer simulations of multiphase flows involving fluids with different properties, such as rheological behaviour and density. These flows may be characterized by challenging features such as impulsive dynamics, fast deformation, sharp interfaces, free-surface separation, interaction with structure, complex 3D geometry. This work illustrates recent advances in the development and application of reliable and fast running numerical models to handle the above-mentioned issues. These meshfree particle models are free and open source and are based on standard Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) method. The first model [5] includes the following features. Alternative formulation of the continuity and momentum equation to treat multiphase flows with high-density ratio. Kernel summation weighted by particle volume instead of density. Renormalization of kernel derivatives by introducing in the continuity equation a diffusive term [4]. This model is compared with a multi-disciplinary simulation software [7] and validated with generation and propagation of a wide variety of regular and non-linear waves in a flume, including impact with fixed structure [3-4]. Multiphase validation is carried out through 2D dam break and 3D full-scale simulation of a fast and large landslide falling in an artificial basin [1]. The second model [6] is an open-source WCSPH code [6] applied to the simulation of three plunging focused wave types impacting onto a floating moored 3D structure [2]. Comparison with experimental data allows validation of time series of wave kinematics, hydrodynamic pressure on the structure and its displacement components, time representation of stress tension on the tethers. The results show that these models can provide thorough and reliable representation of the peculiar feature of the analysed phenomena, thus supporting design applications.