Narrow Results

Water entry problems are very common in engineering and sciences. When objects move with relatively high speed, bubble cavities will be generated, and the behavior of moving objects will also be affected conversely. In this paper, the water entry problems are studied using smoothed particle hydrodynamics (SPH) method, which has special advantages in modeling free surfaces, moving interfaces. First, an improved fluid–solid interface treatment algorithm is presented, whose effectiveness is validated by a water entry of a buoyant cylinder. Then the water entry with different velocities and directions are researched. It is found that the velocities and angles of the moving objects will affect the movement of the object greatly, and the SPH model can give optimal predication of these corresponding conditions.

In this paper, the hydrodynamic behaviors of a typical convex object during water entry are numerically investigated using a meshfree particle method, smoothed particle hydrodynamics (SPH). In order to consider the practical air-cushion effects during water–entry process, a multiphase model with interface force is incorporated to the SPH method to maintain sharp water–air interface. Three numerical examples including bubble rising, water impact on a flate plate and water entry of a wedge are firstly simulated to validate the effectiveness of the multiphase SPH method in predicting the slamming forces and trajectories of falling objects. Water entry of free falling convex objects with different shapes and sizes is then simulated using the validated numerical method for comparative studies. Two slamming processes, including the convex slamming and the structure slamming, are observed in simulations, with double-jetting pattern occurring after the structure slamming. The air-cushion effects are well captured with slamming-induced vortexes clearly shown in the simulation snapshots. Quantitatively, significant drop in pressure peak value is observed when the dimensionless width of the convex is larger than 0.2. Among various shapes of convexes, the square shaped convex experiences the minimal local pressure peak value.

Smoothed Particle Hydrodynamics (SPH) has outstanding advantages in dealing with nonlinear problems. However, it is difficult to find an efficient and accurate non-reflecting boundary for SPH. In this paper, the scaled boundary finite element (SBFE) virtual particle boundary is proposed to model the non-reflecting characteristics of the boundary in SPH. It is implemented by 2–4 layers of SBFE virtual particles whose pressure and velocity are calculated by the Lagrange interpolation from the nearby SBFE nodes. The SBFE virtual particle boundary can effectively and accurately simulate the transmission process of pressure waves on the boundary, and eliminate the influence of the reflecting waves on pressure and velocity fields.