28 research outputs found
Direct Simulations of Wind-Driven Breaking Ocean Waves with Data Assimilation
A formulation is developed to assimilate ocean-wave data into the Numerical
Flow Analysis (NFA) code. NFA is a Cartesian-based implicit Large-Eddy
Simulation (LES) code with Volume of Fluid (VOF) interface capturing. The
sequential assimilation of data into NFA permits detailed analysis of
ocean-wave physics with higher bandwidths than is possible using either other
formulations, such as High-Order Spectral (HOS) methods, or field measurements.
A framework is provided for assimilating the wavy and vortical portions of the
flow. Nudging is used to assimilate wave data at low wavenumbers, and the wave
data at high wavenumbers form naturally through nonlinear interactions, wave
breaking, and wind forcing. Similarly, the vertical profiles of the mean
vortical flow in the wind and the wind drift are nudged, and the turbulent
fluctuations are allowed to form naturally. As a demonstration, the results of
a HOS of a JONSWAP wave spectrum are assimilated to study short-crested seas in
equilibrium with the wind. Log profiles are assimilated for the mean wind and
the mean wind drift. The results of the data assimilations are (1) Windrows
form under the action of breaking waves and the formation of swirling jets; (2)
The crosswind and cross drift meander; (3) Swirling jets are organized into
Langmuir cells in the upper oceanic boundary layer; (4) Swirling jets are
organized into wind streaks in the lower atmospheric boundary layer; (5) The
length and time scales of the Langmuir cells and the wind streaks increase away
from the free surface; (6) Wave growth is very dynamic especially for breaking
waves; (7) The effects of the turbulent fluctuations in the upper ocean on wave
growth need to be considered together with the turbulent fluctuations in the
lower atmosphere; and (8) Extreme events are most likely when waves are not in
equilibrium.Comment: 46 pages, 30th Symposium on Naval Hydrodynamics, Hobart, Tasmania,
Australia, 2-7 November 201
Numerical simulation of transom-stern waves
The flow field generated by a transom-stern hullform is a complex,
broad-banded, three-dimensional phenomenon marked by a large breaking wave.
This unsteady multiphase turbulent flow feature is difficult to study
experimentally and simulate numerically. The results of a set of numerical
simulations, which use the Numerical Flow Analysis (NFA) code, of the flow
around the Model 5673 transom stern at speeds covering both wet- and
dry-transom operating conditions are shown in the accompanying fluid dynamics
video. The numerical predictions for wet-transom and dry-transom conditions are
presented to demonstrate the current state of the art in the simulation of ship
generated breaking waves. The interested reader is referred to Drazen et al.
(2010) for a detailed and comprehensive comparison with experiments conducted
at the Naval Surface Warfare Center Carderock Division (NSWCCD).Comment: Fluid Dynamics Video for 2010 APS Division of Fluid Dynamics Gallery
of Fluid Motion include