Dynamic-Mesh Techniques For Unsteady Multiphase Surface-Ship Hydrodynamics

Open Access
Author:
Casadei, Gina Marie
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 21, 2010
Committee Members:
  • Dr Eric Paterson, Thesis Advisor
Keywords:
  • Multiphase
  • Dynamic-Meshing Techniques
  • CFD
  • Turbulence Modeling
Abstract:
Accurate prediction of transient loads and dynamic response, particularly in high sea states, is of crucial importance when designing ships. Computational Fluid Dynamic (CFD) simulation of dynamic, full-scale, three-dimensional bodies in waves is very challenging and computationally expensive, and empirical seakeeping models are often inaccurate under certain conditions. In naval hydrodynamics, there is a need for robust and fast dynamic-meshing methods appropriate for analyzing maneuvering and seakeeping of ships. CFD methods need to be developed to validate viscous roll-damping models, since the ones used in seakeeping codes have been strictly empirical in the past. A validation study was performed to set the frame-work for understanding viscous dominated flows. These simulations included basic steady and unsteady boundary layer flows for a flat plate and ship-hull geometries. It is critical to prove that the flow solvers are capable of resolving the physics of oscillating flows, boundary layers, and phase lags. The Spalart-Allmaras turbulence model was used for these turbulent flow computations. Four types of dynamic-meshing techniques were selected to study. Dynamic-overset meshing will be compared to three other techniques: dynamic remeshing via solution of a Laplace equation; dynamic remeshing using radial-basis functions (RBF); and mesh motion and dynamic remeshing using a generalized grid interface (GGI). An analysis of the four types of dynamic-meshing techniques was done by quantifying the accuracy, robustness, stability, and speed of each one. While dynamic remeshing via solution of a Laplace equation was robust and GGI was the fastest, overset meshing was found to be the most stable and the most general technique for complex geometries and motions. RBF proved to be too computationally expensive and unrealistic for three-dimensional problems. These methods will be validated with recent experimental data that has been collected at the Naval Surface Warfare Center, Carderock Division (NSWCCD) for a two-dimensional, tumblehome section. Simulation results focus on prescribed roll motion in unsteady, two phase flow. This thesis was completed using OpenFOAM and the foamedOver library, the latter of which is a bridging tool that links SUGGAR and DiRTlib to OpenFOAM for overset meshing.