Search

The treatment of wall boundary conditions is a difficult issue in the SPH method and still represents a challenging topic in the scientific community. After a review of state of the art wall treatment methods, an SPH method for modelling viscous and non-viscous flows in the presence of 3D complex wall boundaries is presented. New developments embedded in the proposed method include the addition of a Laplacian operator adapted to the adopted formalism, as well as a cutface process for calculating the particle/wall interactions on any type of geometry. Validations are proposed on a 2D Poiseuille flow, a flow around a 2D cylinder, a 3D hydrostatic tank, and a 3D dambreak. Comparisons are performed with results from the literature. Finally, an industrial automotive application is presented as illustration of the method ability to deal with arbitrarily complex geometries.

While smoothed-particle hydrodynamics (SPH) simulations are usually performed using uniform particle distributions, local particle refinement techniques have been developed to concentrate fine spatial resolutions in identified areas of interest. Although the formalism of this method is relatively easy to implement, its robustness at coarse/fine interfaces can be problematic. Analysis performed in [16] shows that the radius of refined particles should be greater than half the radius of unrefined particles to ensure robustness. In this article, the basics of an Adaptive Particle Refinement (APR) technique, inspired by AMR in mesh-based methods, are presented. This approach ensures robustness with alleviated constraints. Simulations applying the new formalism proposed achieve accuracy comparable to fully refined spatial resolutions, together with robustness, low CPU times and maintained parallel efficiency.

International audience

International audience

An original strategy to address hydrodynamic flow was recently proposed through a high-order weakly-compressible Cartesian grid approach [1]. The method, named Weakly-Compressible Cartesian hydrodynamics (WCCH), is based on a fully-explicit temporal scheme for solving the Navier-Stokes equations while implicit incompressible schemes are usually preferred in the literature to address such flows. The present study aims to position and compare the WCCH method with a standard incompressible formulation. To this end, an incompressible scheme has been implemented in the same numerical framework. As far as possible, the algorithm used in the incompressible approach has been designed to be the same as (or close to) the one used in the weakly-compressible approach. In particular, high-order schemes for spatial and time discretization are employed. Pros and cons for each formulation are discussed in conjunction with a series of test cases on extensive criteria including implementation convenience, easy use of mesh refinement, convergence order and accuracy, numerical diffusion, parallel CPU scaling for high performance computing, etc. These comparisons demonstrate the relevance of the incompressible approach, at least for the selected test cases. Keywords: Incompressible flows, Pressure Poisson equation, Weakly-compressible approach, Locally refined mesh, Cartesian grid, High-order finite volume

The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian (ALE) smoothed particle hydrodynamics (SPH) model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered: the horizontal velocity, the approach angle (i.e., vertical to horizontal velocity ratio) and the pitch angle, alpha. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen (1993), for small alpha a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle alpha = 4 degrees. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for alpha = 4 degrees and alpha = 10 degrees

International audience

International audience

International audience

International audience

International audience

International audience

Recently, an algorithm for coupling a Finite Volume (FV) method, that discretize the Navier–Stokes equations on block structured Eulerian grids, with the weakly-compressible Lagrangian Smoothed Particle Hydrodynamics (SPH) was presented in [16] . The algorithm takes advantage of the SPH method to discretize flow regions close to free-surfaces and of the FV method to resolve the bulk flow and the wall regions. The continuity between the two solutions is guaranteed by overlapping zones. Here we extend the algorithm by adding the possibility to have: 1) net mass transfer between the SPH and FV sub-domains; 2) free-surface across the overlapping region. In this context, particle generation at common boundaries is required to prevent depletion or clustering of particles. This operation is not trivial, because consistency between the Lagrangian and Eulerian description of the flow must be retained to ensure mass conservation. We propose here a new coupling paradigm that extends the algorithm developed in [16] and renders it suitable to test cases where vorticity and free surface significantly pass from one domain to the other. On the SPH side, a novel technique for the creation/deletion of particle was developed. On the FV side, the information recovered from the SPH solver are exploited to improve free surface prediction in a fashion that resemble the Particle Level-Set algorithms. The combination of the two new features was tested and validated in a number of test cases where both vorticity and front evolution are important. Convergence and robustness of the algorithm are shown.