Input Parameters
The AcoustoDict Johnson–Champoux–Allard Model Options dialog opens when clicking the Options’ Edit… button in the AcoustoDict section.
The options necessary to run the solvers can be entered under the Constituent Materials, Boundary Conditions, Flow Solver, and Diffusion Solver tabs. The command internally has to solve two partial differential equations:
- The Stokes equations to compute the air flow resistivity,
- The Laplace equation to determine the tortuosity.
The Equations and References tab displays further information about the model.
Constituent Materials
Under the Constituent Materials tab, all parameters are as described for the Delany–Bazley model. The Allard–Johnson model also assumes that the fluid in the pore space is air and it should be set that way.
Boundary Conditions
For the Boundary Conditions, in the Computation Directions panel, choose the direction of wave propagation.
Flow Solver
The parameters entered under the Flow Solver tab have the same meaning as described for the Delany–Bazley model.
Diffusion Solver
AcoustoDict solves the Laplace equation to compute tortuosity, diffusivity, and viscous characteristic length. For this, the EJ solver is used.
Simulation Stopping Criterion
The default stopping criterion of the EJ solver, Tolerance, detects if the iterative process becomes stationary. This occurs when the change in the diffusivity value from iteration to iteration becomes extremely small. If the relative change is smaller than the value entered for Tolerance, the iteration is stopped.
When the Residual stopping criterion is used, the iteration is stopped if the solution satisfies the equation up to the required accuracy.
The solver also stops when the Maximal Iterations are done or the Maximal Run Time has been reached. In these situation, no guarantee on the quality of solution can be given.
Which stopping criterion has occurred, can be seen in the Result Viewer of the GeoDict result file (*.gdr) under the Results Map tab.
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Parallelization
Depending on the purchased license, the simulation process can be parallelized.
The Parallelization Options dialog box opens when clicking the Edit... button, to choose between Local, Sequential, Local, Parallel, Local, Maximum, and Cluster.
For details on how to set up und run parallel computations, consult the High Performance Computing handbook.
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Discard PDE Solver File
Checking the Discard PDE Solver Files box causes the deletion of all intermediate computation files. While having the benefit of saving storage place, discarding solver files has also the side effect of disabling the 3D visualization of the results.
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Write Diffusion Flux into Solution File
With Write Diffusion Flux into Solution File, the flux in the three coordinate directions is saved, allowing a detailed analysis of the flux field. The size of the result files increases when selecting this option.
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Equations and References
This tab displays formulas and references which are explained in more detail in the introduction.
