28,089 research outputs found
On algebraic TVD-VOF methods for tracking material interfaces
We revisit simple algebraic VOF methods for advection of material interfaces
based of the well established TVD paradigm. We show that greatly improved
representation of contact discontinuities is obtained through use of a novel
CFL-dependent limiter whereby the classical TVD bounds are exceeded. Perfectly
crisp numerical interfaces are obtained with very limited numerical atomization
(flotsam and jetsam) as compared to previous SLIC schemes. Comparison of the
algorithm with accurate geometrical VOF shows larger error at given mesh
resolution, but comparable efficiency when the reduced computational cost is
accounted for
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
Parallel load balancing strategy for Volume-of-Fluid methods on 3-D unstructured meshes
© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/l Volume-of-Fluid (VOF) is one of the methods of choice to reproduce the interface motion in the simulation of multi-fluid flows. One of its main strengths is its accuracy in capturing sharp interface geometries, although requiring for it a number of geometric calculations. Under these circumstances, achieving parallel performance on current supercomputers is a must. The main obstacle for the parallelization is that the computing costs are concentrated only in the discrete elements that lie on the interface between fluids. Consequently, if the interface is not homogeneously distributed throughout the domain, standard domain decomposition (DD) strategies lead to imbalanced workload distributions. In this paper, we present a new parallelization strategy for general unstructured VOF solvers, based on a dynamic load balancing process complementary to the underlying DD. Its parallel efficiency has been analyzed and compared to the DD one using up to 1024 CPU-cores on an Intel SandyBridge based supercomputer. The results obtained on the solution of several artificially generated test cases show a speedup of up to similar to 12x with respect to the standard DD, depending on the interface size, the initial distribution and the number of parallel processes engaged. Moreover, the new parallelization strategy presented is of general purpose, therefore, it could be used to parallelize any VOF solver without requiring changes on the coupled flow solver. Finally, note that although designed for the VOF method, our approach could be easily adapted to other interface-capturing methods, such as the Level-Set, which may present similar workload imbalances. (C) 2014 Elsevier Inc. Allrights reserved.Peer ReviewedPostprint (author's final draft
The influence of an oil recycler on emissions with oil age for a refuse truck using in service testing
A method of cleaning lubricating oil on line was
investigated using a fine bypass particulate filter followed
by an infra red heater. Two bypass filter sizes of 6 and 1
micron were investigated, both filter sizes were effective
but the one micron filter had the greatest benefit. This
was tested on two nominally identical EURO 1 emissions
compliance refuse trucks, fitted with Perkins Phazer
210Ti 6 litre turbocharged intercooled engines and coded
as RT320 and RT321. These vehicles had emissions
characteristics that were significantly different, in spite of
their similar age and total mileage. RT321 showed an
apparent heavier black smoke than RT320. Comparison
was made with the emissions on the same vehicles and
engines with and without the on-line bypass oil recycler.
Engine exhaust emissions were measured about every
400 miles. Both vehicles started the test with an oil drain
and fresh lubricating oil. The two refuse trucks were
tested in a different sequence, the RT320 without the
recycler fitted and then fitted later and the RT321 with
the recycler fitted and then removed later in the test and
both without any oil change. The RT320 was also the
one with the finer bypass filter. The test mileage was
nearly 8,000 miles both trucks. The air/fuel ratio was
worked out by the exhaust gas analysis. The correlation
between air/fuel ratio and emission parameters was
determined and appropriate corrections were made in
the case of that the air/fuel ratio had an effect on
emissions. The results showed that the on line oil
recycler cleaning system can reduce the rate of increase
of the NOx with oil age. There appeared little influence of
the oil recycler on carbon monoxide and hydrocarbon
emissions. The rate of increase in particulate emissions
was reduced by 50% for RT320 and an immediate
decrease in particulate emissions was seen on RT320
test after fitting the recycler. The black smoke was
reduced by 30% for RT320 in terms average value and
an immediate decrease in smoke after fitting the recycler
on RT320 test and an immediate increase in smoke after
the removal of the recycler on RT321 test were shown
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