G. Oger

Two-dimensional SPH simulations of wedge water entries

This paper presents a study based on the smoothed particles hydrodynamics (SPH) method, aiming at an accurate numerical simulation of solid-fluid coupling in a free surface flow context. The SPH scheme is first described and discussed through its formulations. Then a new technic based on a particle sampling method, and designed to evaluate fluid pressure on solid boundaries is introduced. This method is then extended to the capture of freely moving body dynamics in a fluid/solid coupling approach. This study involves a spatially varying resolution, based on the so-called variable smoothing length technique, for which a new formulation of the equations is proposed. Two distinct test cases of wedge water entry are presented in order to validate this new method. Pressure prediction is first compared with analytical and experimental results, evolution in time of the body dynamics is compared with experimental results in both cases, and the pressure field on the solid boundaries is studied and discussed on the first impact case.

SPH simulation of green water and ship flooding scenarios

Flooding of a ship’s deck (greenwater) or within its internal compartments can severely restrict the operational ability of the vessel, and the safety of its cargo. In severe circumstances such as those produced by freak waves or hull damage, the vessel can become unstable causing it to sink and/or capsize. The flows produced by such events tend to be highly dynamic, with large amounts of free surface deformation. For this reason, SPH is a valuable method for predicting the physics of such flows. In this paper, SPH is used to predict fluid behaviour for two different flooding scenarios. The first is the interaction between a vessel (represented by a rigid body) and undulating travelling waves. The predicted water heights on the deck are compared to experimental results in [1]. The second is the transient flooding behaviour that occurs during, and immediately after a side collision between two vessels. Water heights are measured close to the point of impact within the vessel. The measurements are compared to experimental results in [2].

Adaptive particle refinement and derefinement applied to the smoothed particle hydrodynamics method

SPH simulations are usually performed with a uniform particle distribution. New techniques have been recently proposed to enable the use of spatially varying particle distributions, which encouraged the development of automatic adaptivity and particle refinement/derefinement algorithms. All these efforts resulted in very interesting and promising procedures leading to more efficient and faster SPH simulations. In this article, a family of particle refinement techniques is reviewed and a new derefinement technique is proposed and validated through several test cases involving both free-surface and viscous flows. Besides, this new procedure allows higher resolutions in the regions requiring increased accuracy. Moreover, several levels of refinement can be used with this new technique, as often encountered in adaptive mesh refinement techniques in mesh-based methods.

Parallel computational steering and analysis for HPC applications using a paraview interface and the HDF5 DSM virtual file driver

We present a framework for interfacing an arbitrary HPC simulation code with an interactive ParaView session using the HDF5 parallel IO library as the API. The implementation allows a flexible combination of parallel simulation, concurrent parallel analysis and GUI client, all of which may be on the same or separate machines. Data transfer between the simulation and the ParaView server takes place using a virtual file driver for HDF5 that bypasses the disk entirely and instead communicates directly between the coupled applications in parallel. The simulation and ParaView tasks run as separate MPI jobs and may therefore use different core counts and/or hardware configurations/platforms, making it possible to carefully tailor the amount of resources dedicated to each part of the workload. The coupled applications write and read datasets to the shared virtual HDF5 file layer, which allows the user to read data representing any aspect of the simulation and modify it using ParaView pipelines, then write it back, to be reread by the simulation (or vice versa). This allows not only simple parameter changes, but complete remeshing of grids, or operations involving regeneration of field values over the entire domain, to be carried out. To avoid the problem of manually customizing the GUI for each application that is to be steered, we make use of XML templates that describe outputs from the simulation, inputs back to it, and what user interactions are permitted on the controlled elements. This XML is used to generate GUI and 3D controls for manipulation of the simulation without requiring explicit knowledge of the underlying model.

Violent Fluid-Structure Interaction simulations using a coupled SPH/FEM method

The Smoothed Particle Hydrodynamics (SPH) method presents different key assets for modelling violent Fluid-Structure Interactions (FSI). First, this method is a meshless method, which drastically reduces the complexity of handling the fluid-structure interface when using SPH to model the fluid and coupling it with a Finite Element Method (FEM) for the solid. Second, the method is Lagrangian and large deformations of the fluid domain can thus be followed, which is especially interesting for simulating violent interactions in presence of a free surface, or which induce large deformations, rotations, and translations of the solid. Third, the SPH method being explicit, the time scale of the SPH resolution in the fluid domain is naturally adapted to the FEM resolution in the solid. Free-surface FSIs can also be simulated without including the air phase when it does not play a significative role. For violent interactions where the fluid compressibility matters, it is also intrinsically modelled by the SPH method. The paper details the SPH method used and the coupling. The FEM solver is a standard open source solver for solid mechanics. Validation test cases are then presented in detail. They include the hydrodynamic impact of elastic wedges at high speed, where local pressures and wedge deformations are compared to experimental data.

Parallel Computational Steering for HPC Applications Using HDF5 Files in Distributed Shared Memory

Interfacing a GUI driven visualization/analysis package to an HPC application enables a supercomputer to be used as an interactive instrument. We achieve this by replacing the IO layer in the HDF5 library with a custom driver which transfers data in parallel between simulation and analysis. Our implementation using ParaView as the interface, allows a flexible combination of parallel simulation, concurrent parallel analysis, and GUI client, either on the same or separate machines. Each MPI job may use different core counts or hardware configurations, allowing fine tuning of the amount of resources dedicated to each part of the workload. By making use of a distributed shared memory file, one may read data from the simulation, modify it using ParaView pipelines, write it back, to be reused by the simulation (or vice versa). This allows not only simple parameter changes, but complete remeshing of grids, or operations involving regeneration of field values over the entire domain. To avoid the problem of manually customizing the GUI for each application that is to be steered, we make use of XML templates that describe outputs from the simulation (and inputs back to it) to automatically generate GUI controls for manipulation of the simulation.

A High-Order Finite Volume Solver on Locally Refined Cartesian Meshes—Benchmark Session

This paper provides numerical results of a finite volume solver based on high-order schemes for Cartesian Meshes. This solver is dedicated to the computation of complex flows in marine and ocean engineering. It aims at solving complex hydrodynamic flows that cannot be yet propelery solved such as breaking waves, fluid-structure interactions, turbulent flows, etc. Since high-order schemes are highly recommended for under-resolved simulations, a WENO5 reconstruction is combined with a 4th order Runge–Kutta scheme for time integration.

Smoothed Particle Hydrodynamics: benchmarking on selected test cases within the NextMuSE initiative

In this paper are presented comparisons of SPH variants on academic test cases classically used to validate numerical fluid dynamics software. These comparisons are extracted from NextMuSE FP7 project activities which will be published more extensively in the near future. One of the goals of this project was to better understand the SPH method and to leave the path to its establishment within CFD methods. An important work load was thus dedicated to benchmark SPH variants on selected test cases.A number of results and conclusions of this comparative study are presented in this paper. The studied variants are: standard weekly-compressible SPH, δ-SPH, Riemann-SPH, incompressible SPH, and FVPM. The majority of the test cases also present a reference solution, either experimental or computed using a mesh-based solver. Test cases include: wave propagation, flow past a cylinder, jet impact, floating body, bubble rise, dam break on obstacle, floating body dynamics, etc. Conclusions may help SPH practitioners to choose one variant or another and shall give detailed understanding necessary to derive further improvements of the method.Copyright