A compressible two-phase flow model for pressure oscillations in air entrapments following green water impact events on ships

Journal article (2020)

Authors

M. van der Eijk Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering
P.R. Wellens Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering
Research Group
Ship Hydromechanics and Structures (Mechanical, Maritime and Materials Engineering) (TU Delft)
CFD Surface tension Wave impact Volume-of-Fluid Compressible two-phase flow Dam-break
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Published Date

2020

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Marine and Transport Technology

Research Group

Ship Hydromechanics and Structures

Abstract

A significant part of all structural damage to conventional ships is caused by complex free-surface events like slamming, breaking waves, and green water. During these events air can be entrapped by water. The focus of this article is on the resulting air pockets affecting the evolution of the hydrodynamic impact pressure that loads the ship's structure. ComFLOW is a computationally efficient method based on the Navier-Stokes equations with a Volume-of-Fluid approach for the free surface, designed to perform multiphase simulations of extreme free surface wave interaction with maritime structures. We have extended ComFLOW with a Continuum Surface Force (CSF) model for surface tension, thereby completing our method for representing gas-water interaction after free surface wave impacts. The implementation was verified with benchmark cases addressing all relevant aspects of the dynamics of entrapped air pockets. The implementation was validated by means of a dam-break experiment, a characteristic model for green water impact events. The method-having been verified and validated-was applied to a dam-break simulation for a different setting in which the impact on a wall leads to an entrapped air pocket. Surface tension was found not to have an influence on entrapped air pocket dynamics of air pockets with a radius larger than 0.08 [m]. For wave impacts it was found that the effect of compression waves in the air pocket dominates the dynamics and leads to pressure oscillations that are of the same order of magnitude as the pressure caused by the initial impact on the base of the wall. The code is available at: https://github.com/martin-eijk/2phase.git.