45,693 research outputs found
Consistent forcing scheme in the cascaded lattice Boltzmann method
In this paper, we give a more pellucid derivation for the cascaded lattice
Boltzmann method (CLBM) based on a general multiple-relaxation-time (MRT) frame
through defining a shift matrix. When the shift matrix is a unit matrix, the
CLBM degrades into an MRT LBM. Based on this, a consistent forcing scheme is
developed for the CLBM. The applicability of the non-slip rule, the
second-order convergence rate in space and the property of isotropy for the
consistent forcing scheme is demonstrated through the simulation of several
canonical problems. Several other existing force schemes previously used in the
CLBM are also examined. The study clarifies the relation between MRT LBM and
CLBM under a general framework
Algorithm for Computing Excited States in Quantum Theory
Monte Carlo techniques have been widely employed in statistical physics as
well as in quantum theory in the Lagrangian formulation. However, in the
conventional approach, it is extremely difficult to compute the excited states.
Here we present a different algorithm: the Monte Carlo Hamiltonian method,
designed to overcome the difficulties of the conventional approach. As a new
example, application to the Klein-Gordon field theory is shown.Comment: 3 pages, uses Latex and aipproc.cl
Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model
Owing to its conceptual simplicity and computational efficiency, the
pseudopotential multiphase lattice Boltzmann (LB) model has attracted
significant attention since its emergence. In this work, we aim to extend the
pseudopotential LB model to simulate multiphase flows at large density ratio
and relatively high Reynolds number. First, based on our recent work [Li et
al., Phys. Rev. E. 86, 016709 (2012)], an improved forcing scheme is proposed
for the multiple-relaxation-time pseudopotential LB model in order to achieve
thermodynamic consistency and large density ratio in the model. Next, through
investigating the effects of the parameter a in the Carnahan-Starling equation
of state, we find that the interface thickness is approximately proportional to
1/sqrt(a). Using a smaller a will lead to a wider interface thickness, which
can reduce the spurious currents and enhance the numerical stability of the
pseudopotential model at large density ratio. Furthermore, it is found that a
lower liquid viscosity can be gained in the pseudopotential model by increasing
the kinematic viscosity ratio between the vapor and liquid phases. The improved
pseudopotential LB model is numerically validated via the simulations of
stationary droplet and droplet oscillation. Using the improved model as well as
the above treatments, numerical simulations of droplet splashing on a thin
liquid film are conducted at a density ratio in excess of 500 with Reynolds
numbers ranging from 40 to 1000. The dynamics of droplet splashing is correctly
reproduced and the predicted spread radius is found to obey the power law
reported in the literature.Comment: 9 figures, 2 tables, accepted by Physical Review E (in press
Modeling incompressible thermal flows using a central-moment-based lattice Boltzmann method
In this paper, a central-moment-based lattice Boltzmann (CLB) method for
incompressible thermal flows is proposed. In the method, the incompressible
Navier-Stokes equations and the convection-diffusion equation for the
temperature field are sloved separately by two different CLB equations. Through
the Chapman-Enskog analysis, the macroscopic governing equations for
incompressible thermal flows can be reproduced. For the flow field, the tedious
implementation for CLB method is simplified by using the shift matrix with a
simplified central-moment set, and the consistent forcing scheme is adopted to
incorporate forcing effects. Compared with several D2Q5
multiple-relaxation-time (MRT) lattice Boltzmann methods for the temperature
equation, the proposed method is shown to be better Galilean invariant through
measuring the thermal diffusivities on a moving reference frame. Thus a higher
Mach number can be used for convection flows, which decreases the computational
load significantly. Numerical simulations for several typical problems confirm
the accuracy, efficiency, and stability of the present method. The grid
convergence tests indicate that the proposed CLB method for incompressible
thermal flows is of second-order accuracy in space
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