98 research outputs found
Fluid-structure interaction by a coupled lattice Boltzmann-finite element approach
In this thesis, a strategy to model the behavior of fluids and their interaction with deformable bodies is proposed. The fluid domain is modeled by using the lattice Boltzmann method, thus analyzing the fluid dynamics by a mesoscopic point of view. It has been proved that the solution provided by this method is equivalent to solve the Navier-Stokes equations for an incompressible flow with a second-order accuracy. Slender elastic structures idealized through beam finite elements are used. Large displacements are accounted for by using the corotational formulation. Structural dynamics is computed by using the Time Discontinuous Galerkin method. Therefore, two different solution procedures are used, one for the fluid domain and the other for the structural part, respectively. These two solvers need to communicate and to transfer each other several information, i.e. stresses, velocities, displacements. In order to guarantee a continuous, effective, and mutual exchange of information, a coupling strategy, consisting of three different algorithms, has been developed and numerically tested. In particular, the effectiveness of the three algorithms is shown in terms of interface energy artificially produced by the approximate fulfilling of compatibility and equilibrium conditions at the fluid-structure interface.
The proposed coupled approach is used in order to solve different fluid-structure interaction problems, i.e. cantilever beams immersed in a viscous fluid, the impact of the hull of the ship on the marine free-surface, blood flow in a deformable vessels, and even flapping wings simulating the take-off of a butterfly. The good results achieved in each application highlight the effectiveness of the proposed methodology and of the C++ developed software to successfully approach several two-dimensional fluid-structure interaction problems
Advanced lattice Boltzmann scheme for high-Reynolds-number magneto-hydrodynamic flows
International audienceIs the lattice Boltzmann method suitable to investigate numerically high-Reynolds-number magneto-hydrodynamic (MHD) ows? It is shown that a standard approach based on the Bhatnagar-Gross-Krook (BGK) collision operator rapidly yields unstable simulations as the Reynolds number increases. In order to circumvent this limitation, it is here suggested to address the collision procedure in the space of central moments for the uid dynamics. Therefore, an hybrid LB scheme is introduced, which couples a central-moment scheme for the velocity with a BGK scheme for the space-and-time evolution of the magnetic field. This method outperforms the standard approach in terms of stability, allowing us to simulate high-Reynolds-number MHD ows with non-unitary Prandtl number while maintaining accuracy and physical consistency
Three-dimensional central-moments-based lattice Boltzmann method with external forcing: A consistent, concise and universal formulation
The cascaded or central-moments-based lattice Boltzmann method (CM-LBM) is a
robust alternative to the more conventional BGK-LBM for the simulation of
high-Reynolds number flows. Unfortunately, its original formulation makes its
extension to a broader range of physics quite difficult. To tackle this issue,
a recent work [A. De Rosis, Phys. Rev. E 95, 013310 (2017)] proposed a more
generic way to derive concise and efficient three-dimensional CM-LBMs. Knowing
the original model also relies on central moments that are derived in an adhoc
manner, i.e., by mimicking those of the Maxwell-Boltzmann distribution to
ensure their Galilean invariance a posteriori, a very recent effort [A. De
Rosis and K. H. Luo, Phys. Rev. E 99, 013301 (2019)] was proposed to further
generalize their derivation. The latter has shown that one could derive
Galilean invariant CMs in a systematic and a priori manner by taking into
account high-order Hermite polynomials in the derivation of the discrete
equilibrium state. Combining these two approaches, a compact and mathematically
sound formulation of the CM-LBM with external forcing is proposed. More
specifically, the proposed formalism fully takes advantage of the D3Q27
discretization by relying on the corresponding set of 27 Hermite polynomials
(up to the sixth order) for the derivation of both the discrete equilibrium
state and the forcing term. The present methodology is more consistent than
previous approaches, as it properly explains how to derive Galilean invariant
CMs of the forcing term in an a priori manner. Furthermore, while keeping the
numerical properties of the original CM-LBM, the present work leads to a
compact and simple algorithm, representing a universal methodology based on CMs
and external forcing within the lattice Boltzmann framework.Comment: Published in Phys. Fluids as Editor's Pic
Efficient kinetic Lattice Boltzmann simulation of three-dimensional Hall-MHD Turbulence
Simulating plasmas in the Hall-MagnetoHydroDynamics (Hall-MHD) regime
represents a valuable {approach for the investigation of} complex non-linear
dynamics developing in astrophysical {frameworks} and {fusion machines}. Taking
into account the Hall electric field is {computationally very challenging as}
it involves {the integration of} an additional term, proportional to \bNabla
\times ((\bNabla\times\mathbf{B})\times \mathbf{B}) in the Faraday's induction
{law}. {The latter feeds back on} the magnetic field at small
scales (between the ion and electron inertial scales), {requiring} very high
resolution{s} in both space and time {in order to properly describe its
dynamics.} The computational {advantage provided by the} kinetic Lattice
Boltzmann (LB) approach is {exploited here to develop a new} code, the
\textbf{\textsc{F}}ast \textbf{\textsc{L}}attice-Boltzmann
\textbf{\textsc{A}}lgorithm for \textbf{\textsc{M}}hd
\textbf{\textsc{E}}xperiments (\textsc{flame}). The \textsc{flame} code
integrates the plasma dynamics in lattice units coupling two kinetic schemes,
one for the fluid protons (including the Lorentz force), the other to solve the
induction equation describing the evolution of the magnetic field. Here, the
newly developed algorithm is tested against an analytical wave-solution of the
dissipative Hall-MHD equations, pointing out its stability and second-order
convergence, over a wide range of the control parameters. Spectral properties
of the simulated plasma are finally compared with those obtained from numerical
solutions from the well-established pseudo-spectral code \textsc{ghost}.
Furthermore, the LB simulations we present, varying the Hall parameter,
highlightthe transition from the MHD to the Hall-MHD regime, in excellent
agreement with the magnetic field spectra measured in the solar wind
Color-gradient lattice Boltzmann model with nonorthogonal central moments: Hydrodynamic melt-jet breakup simulations
We develop a lattice Boltzmann (LB) model for immiscible two-phase flow simulations with central moments (CMs). This successfully combines a three-dimensional nonorthogonal CM-based LB scheme [De Rosis, Phys. Rev. E 95, 013310 (2017)] with our previous color-gradient LB model [Saito, Abe, and Koyama, Phys. Rev. E 96, 013317 (2017)]. Hydrodynamic melt-jet breakup simulations show that the proposed model is significantly more stable, even for flow with extremely high Reynolds numbers, up to O(106). This enables us to investigate the phenomena expected under actual reactor conditions
Color-gradient lattice Boltzmann model with nonorthogonal central moments: Hydrodynamic melt-jet breakup simulations
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