63,847 research outputs found
Viscous heating effects in fluids with temperature-dependent viscosity: triggering of secondary flows
Viscous heating can play an important role in the dynamics of fluids with
strongly temperature-dependent viscosities because of the coupling between the
energy and momentum equations. The heat generated by viscous friction produces
a local temperature increase near the tube walls with a consequent decrease of
the viscosity and a strong stratification in the viscosity profile. The problem
of viscous heating in fluids was investigated and reviewed by Costa & Macedonio
(2003) because of its important implications in the study of magma flows.
Because of the strong coupling between viscosity and temperature, the
temperature rise due to the viscous heating may trigger instabilities in the
velocity field, which cannot be predicted by a simple isothermal Newtonian
model. When viscous heating produces a pronounced peak in the temperature
profile near the walls, a triggering of instabilities and a transition to
secondary flows can occur because of the stratification in the viscosity
profile. In this paper we focus on the thermal and mechanical effects caused by
viscous heating. We will present the linear stability equations and we will
show, as in certain regimes, these effects can trigger and sustain a particular
class of secondary rotational flows which appear organised in coherent
structures similar to roller vortices. This phenomenon can play a very
important role in the dynamics of magma flows in conduits and lava flows in
channels and, to our knowledge, it is the first time that it has been
investigated by a direct numerical simulation.Comment: 18 pages manuscript, 10 figures, to be published in Journal of Fluid
Mechanics (2005
Combinatorial formulation of Ising model revisited
In 1952, Kac and Ward developed a combinatorial formulation for the two
dimensional Ising model which is another method of obtaining Onsager's formula
for the free energy per site in the thermodynamic limit of the model. Feynman
gave an important contribution to this formulation conjecturing a crucial
mathematical relation which completed Kac and Ward ideas. In this paper, the
method of Kac, Ward and Feynman for the free field Ising model in two
dimensions is reviewed in a selfcontained way.Comment: 27 pages, 17 figure
Energy dissipation and equivalent damping of RC columns subjected to biaxial bending: an investigation based in experimental results
The cyclic behaviour of reinforced concrete columns have been object of many experimental studies in the
recent past years. However, the experimental studies on the biaxial response of RC columns are still limited. In
this paper are presented the main results of an experimental study of 24 full-scale rectangular building columns
tested for different loading paths under uniaxial and biaxial conditions. The experimental results are presented
and discussed in terms of global behaviour, particularly focusing on the stiffness and strength degradation due to
the increasing cyclic demand, and energy dissipation evolution. The equivalent viscous damping was estimated
based on the experimental results of the RC columns tested under biaxial loading and empirical expressions are proposed
Induced higher-derivative massive gravity on a 2-brane in 4D Minkowski space
In this paper we revisit the problem of localizing gravity in a 2-brane
embedded in a 4D Minkowski space to address induction of high derivative
massive gravity. We explore the structure of propagators to find well-behaved
higher-derivative massive gravity induced on the brane. Exploring a special
case in the generalized mass term of the graviton propagator we find a model of
consistent higher order gravity with an additional unitary massive spin-2
particle and two massless particles: one spin-0 particle and one spin-1
particle. The condition for the absence of tachyons is satisfied for both
`right' and `wrong' signs of the Einstein-Hilbert term on the 2-brane. We also
find the Pauli-Fierz mass term added to the new massive gravity in three
dimensions and recover the low dimensional DGP model.Comment: Latex, 12 pages, no figure; refs added, version to appear in PL
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