Computation of Viscous Multiphase Hydrodynamics and Ship Motions During Wave-Slap Events and Wave Excited Roll

Open Access
Author:
Smith, Kevin
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Eric Paterson, Thesis Advisor
Keywords:
  • wave breaking
  • tumblehome
  • oscillating cylinder
  • prescribed motion
  • RANS
  • CFD
  • VOF
  • 6DOF
  • seakeeping
  • wave impact
  • wave model
  • free surface
  • sponge layer
  • numerical beach
  • dissipation zone
  • box barge
  • mesh motion
  • deep water
  • shallow water
  • non reflecting boundary condition
  • openfoam
  • finite volume method
  • wave dissipation
  • impact load scaling
Abstract:
There is a need for computational tools which can accurately predict non-linear ship motions and wave-impact loads. Lateral ship motions (roll, sway, and yaw) can be very non-linear in nature due to viscous effects and flow separation. Roll damping is especially important to predict because it is critical to the stability of a ship in waves. Roll damping is primarily due to viscous effects, which are not resolvable using potential flow methods. Wave impact loads, or “wave-slap”, can damage a ship’s hull and deck structures and the frequency and magnitude of the loads can be coupled with the ship motions. The objective of this thesis is to provide the building blocks of a computational seakeeping model which can predict the motions of a ship at sea including the effect of large amplitude waves. A seakeeping model is made up of several fundamental building blocks or component models. The components developed and tested in the present work include a wave maker boundary condition, a non-reflecting boundary, dynamic mesh motion, and 6DOF rigid- body motion. A second order Stokes deep water wave maker boundary condition is de- veloped and several tests are presented to study and validate the model. A non-reflecting boundary technique known as a numerical sponge layer is developed and tested to show that wave reflections can be reduced below 5% of the incoming wave amplitude. A 6DOF motion solver is developed and coupled with the pre-existing mesh motion techniques. The validity of the 6DOF model is proven using free-decay and wave-excited numerical experi- ments of a floating 2D rectangular box barge. Wave-impact phenomena are studied using a dam break case and a practical example of a wave impacting a floating block. Several studies are performed to examine grid dependency and scaling effects. All components are developed within the OpenFOAM platform using a fully viscous and turbulent multi-phase fluid model.