Session: 08-05-02 Free Surface Flows II

Paper Number: 80796

80796 - Enhancements of Computational Fluid Dynamics Analysis of Air Entrapment and Fluid-Structure Interaction During Plate Entry to Water Through VoF-Slip and Adaptive Discretization Schemes 

A Computational Fluid Dynamics (CFD) analysis of air entrapment and structural responses during plate
entry to water is presented. Slamming loads remain of concern for the design of safe and efficient ships and
offshore structures, e.g. to ensure structural integrity during extreme events or reduce structural weight.
Besides ships with large bow flare or horizontal stern planes, slamming events also occur for fast small
craft currently receiving increasing attention in the community. Ditching of airplanes or vehicle wading are
relevant applications in other industries.
The advance of computational methods in engineering has enabled numerical analysis of fluid-structure
interaction (FSI) problems such as slamming. A crucial task of solving the coupled fluid and structural
problem is the accurate resolution of free surface dynamics including phase interactions between water and
air. Air entrapment does not only affect the pressure distribution during impact but can also be generated
artificially (numerical ventilation) in numerical methods. The study at hand was based on a Finite-Volume
(FV) method and the numerical solution of Reynolds-averaged Navier-Stokes (RANS) equations. Emphasis
was laid on numerical techniques to contain numerical ventilation whilst limiting the increase in
computational cost. In doing so, adaptive discretization schemes were employed. Namely, model-based
adaptive mesh refinement (AMR) and time stepping for both motions of bodies (rigid or elastic) and the
free surface. Additionally, the underlying Volume of Fluid (VoF) method was enhanced through
consideration of slip between water and air. Comparison was drawn to two novel experimental analyses for
which both structural responses and high-resolution imagery of air entrapment and spray were available. It
was demonstrated that above enhancements not only lead to better capturing of air entrapment and reduced
numerical ventilation, whilst retaining accuracy levels, but also offered more flexible modeling concepts
and potential performance gains. Since both spatial and temporal evolution of the displaced water are
generally unknown, usually large grid refinement zones are employed to ensure the interface remains
resolved, resulting in high cell count and computing times. Comparison of structural responses were found
to be favorable for both CFD methods.

Presenting Author: Philipp Mucha Siemens Digital Industries Software

Authors:

Philipp Mucha Siemens Digital Industries Software
Minyee Jiang NSWC, Carderock Division
Raymond Bay NSWC, Carderock Division