An overset mesh based multiphase flow solver for water entry problems

This paper extends a recently proposed multi-region based numerical wave tank (Martínez-Ferrer et al., 2016 [1]) to solve water entry problems in naval engineering. The original static linking strategy is developed to enable the dynamic coupling of several moving regions. This permits the method to deal with large-amplitude motions for structures slamming into water waves. A background grid and one or more component meshes are firstly generated to overlay the whole computational domain and the sub-domains surrounding the structures, respectively. During computation, the background mesh is fixed while the small grids move freely or as prescribed without deformation and regeneration. This effectively circumvents the large and often excessive error-prone dynamic deformation of a single-block mesh as well as the complex and time-consuming mesh regeneration. Test cases of dam breaking with and without obstacles are first conducted to verify the developed code by comparing the numerical solution against experimental data. Then the new code is used to solve prescribed and free-fall water entry problems. The obtained results agree well with experimental measurements and other computational results reported in the literature

A generalized finite difference scheme for multiphase flow

This paper presents a GPU-based, incompressible, multiphase generalized finite difference solver for simulating multiphase flow. The method includes a dampening scheme that allows for large density ratio cases to be simulated. Two verification studies are performed by simulating the relaxation of a square droplet surrounded by a light fluid and a bubble rising in a denser fluid. The scheme is also used to simulate the collision of binary droplets at moderate Reynolds numbers (250–550). The effects of the surface tension and density ratio are explored in this work by considering cases withWeber numbers of 8 and 180 and density ratios of 2:1 and 1000:1. The robustness of the multiphase scheme is highlighted when resolving thin fluid structures arising in both high and low density ratio cases at We = 180.University of Pretoria Co-Funding Postdoctoral Fellowship Programme.http://www.mdpi.com/journal/mcaMechanical and Aeronautical EngineeringSDG-09: Industry, innovation and infrastructur

Probabilistic tsunami hazard assessment: quantifying uncertainty in landslide generated waves

Landslide generated waves (LGWs) have many associated uncertainties that need to be ac- counted for during a hazard analysis. The work presented in this thesis developed and applied numerical modelling techniques to investigate and quantify these sources of uncertainty. Firstly, to model the LGW source as a deformable slide, a smoothed particle hydrodynamics (SPH) simulator was improved and adapted. The simulator was tested using lab scale bench- marks and an idealised full scale LGW scenario. The effects of landslide source parameters on the wave at increasing scales were then investigated. In order to make use of the findings regarding complex LGW source models, a probabilistic sensitivity analysis on the full range of source parameters and their effect on the generated wave was performed using the SPH simulator. This showed that the geometric landslide parameters (such as volume and submergence depth) contributed more to uncertainty in the resulting wave characteristics near the source than the rheological parameters. By coupling different wave propagation models to the results from the near-field SPH simulator, it was revealed that the choice of mathematical formulation for propagation made a significant difference to which parameters affected the inundation level the most. These findings have important implications for the design of future LGW modelling studies and which parts of the model workflow should have more computational cost dedicated to them. Near the source the landslide geometry outweighs the complexity of the rheological model in terms of influence on the wave characteristics. During propagation the mathematical formulation chosen can have a large influence on results, so dedicating extra computational cost to this phase would be worthwhile.Open Acces