Guide

The FinEtools package is used here to solve linear acoustics problems.

Tutorials are provided in the form of Julia scripts and Markdown files in a dedicated folder: index of tutorials.

Modules

The package FinEtoolsAcoustics has the following structure:

• Top-level: FinEtoolsAcoustics is the top-level module.

• Acoustics: AlgoAcoustModule (algorithms), FEMMAcoustModule, FEMMAcoustSurfModule (FEM machines to evaluate the matrix and vector quantities), MatAcoustFluidModule (acoustic fluid material).

Acoustics FEM machines

There is one for the interior integrals and one for boundary integrals. The machine for the interior integrals can be used to compute:

• Evaluate the acoustic-mass matrix and the acoustic-stiffness matrix.

The machine for the boundary integrals can be used to compute:

• Compute transformation matrix to convert pressure to resultant force or pressure to resultant torque.
• Compute the acoustic ABC (absorbing boundary condition) matrix.
• Compute the acoustic Robin boundary condition matrix.

Acoustics algorithms

At the moment there is one algorithm, for steady-state (harmonic) acoustics.

Example: baffled piston

After the mesh has been generated, the modeldata can be set up: Here we begin with the region.

material = MatAcoustFluid(bulk, rho)
region1 =  FDataDict("femm"=>FEMMAcoust(IntegDomain(fes, GaussRule(3, 2)), material))

We set up a definition of the absorbing boundary condition:

abc1  =  FDataDict("femm"=>FEMMAcoustSurf(IntegDomain(outer_fes, GaussRule(2, 2)),
          material))

The surface of the piston is associated with a known-flux boundary condition (prescribed normal component of the velocity):

flux1  =  FDataDict("femm"=>FEMMAcoustSurf(IntegDomain(piston_fes, GaussRule(2, 2)),
          material),  "normal_flux"=> -1.0im*rho*omega*v_piston);

And finally we make the model data,

modeldata =  FDataDict("fens"=>  fens,
                 "omega"=>omega,
                 "regions"=>[region1],
                 "flux_bcs"=>[flux1], "ABCs"=>[abc1])

and call the solver:

modeldata = FinEtools.AlgoAcoustModule.steadystate(modeldata)

When the algorithm completes, modeldata["P"] is the computed pressure field.