1,191 research outputs found
Linear stability analysis of capillary instabilities for concentric cylindrical shells
Motivated by complex multi-fluid geometries currently being explored in
fibre-device manufacturing, we study capillary instabilities in concentric
cylindrical flows of fluids with arbitrary viscosities, thicknesses,
densities, and surface tensions in both the Stokes regime and for the full
Navier--Stokes problem. Generalizing previous work by Tomotika (N=2), Stone &
Brenner (N=3, equal viscosities) and others, we present a full linear stability
analysis of the growth modes and rates, reducing the system to a linear
generalized eigenproblem in the Stokes case. Furthermore, we demonstrate by
Plateau-style geometrical arguments that only axisymmetric instabilities need
be considered. We show that the N=3 case is already sufficient to obtain
several interesting phenomena: limiting cases of thin shells or low shell
viscosity that reduce to N=2 problems, and a system with competing breakup
processes at very different length scales. The latter is demonstrated with full
3-dimensional Stokes-flow simulations. Many cases remain to be
explored, and as a first step we discuss two illustrative cases,
an alternating-layer structure and a geometry with a continuously varying
viscosity
Simulation of flows with violent free surface motion and moving objects using unstructured grids
This is the peer reviewed version of the following article: [Löhner, R. , Yang, C. and Oñate, E. (2007), Simulation of flows with violent free surface motion and moving objects using unstructured grids. Int. J. Numer. Meth. Fluids, 53: 1315-1338. doi:10.1002/fld.1244], which has been published in final form at https://doi.org/10.1002/fld.1244. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.A volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The present implementation follows the classic VOF implementation for the liquid–gas system, considering only the liquid phase. Extrapolation algorithms are used to obtain velocities and pressure in the gas region near the free surface. The VOF technique is validated against the classic dam-break problem, as well as series of 2D sloshing experiments and results from SPH calculations. These and a series of other examples demonstrate that the ability of the present approach to simulate violent free surface flows with strong nonlinear behaviour.Peer ReviewedPostprint (author's final draft
An implicit finite-element model for 3D non-hydrostatic mesoscale ocean flows
We present in this paper a pressure stabilized, finite element
method for the numerical approximation of three-dimensional,
non-hydrostatic mesoscale ocean flows. The model considered here
incorporates surface wind stress, bottom friction and Coriolis
acceleration, and it is applicable to irregular bottom
topographies. An implicit unconditionally stable scheme is
employed for the time advancement and an anisotropic stabilization
technique is used for the spatial finite element discretization.
The numerical results obtained on test cases demonstrate the
robustness and accuracy of the method proposed here
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