3,946 research outputs found
High-order DG solvers for under-resolved turbulent incompressible flows: A comparison of and (div) methods
The accurate numerical simulation of turbulent incompressible flows is a
challenging topic in computational fluid dynamics. For discretisation methods
to be robust in the under-resolved regime, mass conservation as well as energy
stability are key ingredients to obtain robust and accurate discretisations.
Recently, two approaches have been proposed in the context of high-order
discontinuous Galerkin (DG) discretisations that address these aspects
differently. On the one hand, standard -based DG discretisations enforce
mass conservation and energy stability weakly by the use of additional
stabilisation terms. On the other hand, pointwise divergence-free
-conforming approaches ensure exact mass conservation
and energy stability by the use of tailored finite element function spaces. The
present work raises the question whether and to which extent these two
approaches are equivalent when applied to under-resolved turbulent flows. This
comparative study highlights similarities and differences of these two
approaches. The numerical results emphasise that both discretisation strategies
are promising for under-resolved simulations of turbulent flows due to their
inherent dissipation mechanisms.Comment: 24 pages, 13 figure
Energy stability analysis for a hybrid fluid-kinetic plasma model
In plasma physics, a hybrid fluid-kinetic model is composed of a
magnetohydrodynamics (MHD) part that describes a bulk fluid component and a
Vlasov kinetic theory part that describes an energetic plasma component. While
most hybrid models in the plasma literature are non-Hamiltonian, this paper
investigates a recent Hamiltonian variant in its two-dimensional configuration.
The corresponding Hamiltonian structure is described along with its Casimir
invariants. Then, the energy-Casimir method is used to derive explicit
sufficient stability conditions, which imply a stable spectrum and suggest
nonlinear stability
Exact energy stability of B\'enard-Marangoni convection at infinite Prandtl number
Using the energy method we investigate the stability of pure conduction in
Pearson's model for B\'enard-Marangoni convection in a layer of fluid at
infinite Prandtl number. Upon extending the space of admissible perturbations
to the conductive state, we find an exact solution to the energy stability
variational problem for a range of thermal boundary conditions describing
perfectly conducting, imperfectly conducting, and insulating boundaries. Our
analysis extends and improves previous results, and shows that with the energy
method global stability can be proven up to the linear instability threshold
only when the top and bottom boundaries of the fluid layer are insulating.
Contrary to the well-known Rayleigh-B\'enard convection setup, therefore,
energy stability theory does not exclude the possibility of subcritical
instabilities against finite-amplitude perturbations.Comment: 11 pages, 2 figures. Preprint submitted to the Journal of Fluid
Mechanics. Version 2: minor text and notational changes, added a new appendix
A, added detail to Section
Tuning Bandgap and Energy Stability of Organic-Inorganic Halide Perovskites through Surface Engineering
Organohalide perovskite with a variety of surface structures and morphologies
have shown promising potential owing to the choice of the type of
heterostructure dependent stability. We systematically investigate and discuss
the impact of 2-dimensional molybdenum-disulphide (MoS2), molybdenum-diselenide
(MoSe2), tungsten-disulphide (WS2), tungsten-diselenide (WSe2), boron- nitiride
(BN) and graphene monolayers on band-gap and energy stability of
organic-inorganic halide perovskites. We found that MAPbI3ML deposited on BN-ML
shows room temperature stability (-25 meV~300K) with an optimal bandgap of ~1.6
eV. The calculated absorption coefficient also lies in the visible-light range
with a maximum of 4.9 x 104 cm-1 achieved at 2.8 eV photon energy. On the basis
of our calculations, we suggest that the encapsulation of an organic-inorganic
halide perovskite monolayers by semiconducting monolayers potentially provides
greater flexibility for tuning the energy stability and the bandgap.Comment: 19 pages (single sided), 5 figures, 1 Tabl
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