5 research outputs found
Boundary Element and Finite Element Coupling for Aeroacoustics Simulations
We consider the scattering of acoustic perturbations in a presence of a flow.
We suppose that the space can be split into a zone where the flow is uniform
and a zone where the flow is potential. In the first zone, we apply a
Prandtl-Glauert transformation to recover the Helmholtz equation. The
well-known setting of boundary element method for the Helmholtz equation is
available. In the second zone, the flow quantities are space dependent, we have
to consider a local resolution, namely the finite element method. Herein, we
carry out the coupling of these two methods and present various applications
and validation test cases. The source term is given through the decomposition
of an incident acoustic field on a section of the computational domain's
boundary.Comment: 25 page
Coupling Linear Sloshing with Six Degrees of Freedom Rigid Body Dynamics
Fluid motion in tanks is usually described in space industry with the
so-called Lomen hypothesis which assumes the vorticity is null in the moving
frame. We establish in this contribution that this hypothesis is valid only for
uniform rotational motions. We give a more general formulation of this coupling
problem, with a compact formulation. We consider the mechanical modeling of a
rigid body with a motion of small amplitude, containing an incompressible fluid
in the linearized regime. We first establish that the fluid motion remains
irrotational in a Galilean referential if it is true at the initial time. When
continuity of normal velocity and pressure are prescribed on the free surface,
we establish that the global coupled problem conserves an energy functional
composed by three terms. We introduce the Stokes - Zhukovsky vector fields,
solving Neumann problems for the Laplace operator in the fluid in order to
represent the rotational rigid motion with irrotational vector fields. Then we
have a good framework to consider the coupled problem between the fluid and the
rigid motion. The coupling between the free surface and the ad hoc component of
the velocity potential introduces a "Neumann to Dirichlet" operator that allows
to write the coupled system in a very compact form. The final expression of a
Lagrangian for the coupled system is derived and the Euler-Lagrange equations
of the coupled motion are presented.Comment: 23 page
H-Matrix Solver Applied to Coupled FEM-BEM Aeroacoustics Simulations
International audienc
Stable Perfectly Matched Layers with Lorentz transformation for the convected Helmholtz equation
International audiencePerfectly Matched Layers (PMLs) appear as a popular alternative to non-reflecting boundary conditions for wave-type problems. The core idea is to extend the computational domain by a fictitious layer with specific absorption properties such that the wave amplitude decays significantly and does not produce back reflections. In the context of convected acoustics, it is well-known that PMLs are exposed to stability issues in the frequency and time domain. It is caused by a mismatch between the phase velocity on which the PML acts, and the group velocity which carries the energy of the wave. The objective of this study is to take advantage of the Lorentz transformation in order to design stable perfectly matched layers for generally shaped convex domains in a uniform mean flow of arbitrary orientation. We aim at presenting a pedagogical approach to tackle the stability issue. The robustness of the approach is also demonstrated through several two-dimensional high-order finite element simulations of increasing complexity