Difference between revisions of "OpenPSTD v1.0 settings"
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When an edge of the constructed configuration is selected, see [[Getting started with
When an edge of the constructed configuration is selected, see [[Getting started with ]] how to do this, the acoustic absorption coefficient can be assigned to this edge by setting the '''Absorption''' to a value between 0 and 1. When an edge is selected, the actual value of the absorption coefficient of this edge is written in parenthesis behind the '''Absorption''' setting. In [[openPSTD v1.0 overview]], it is explained how reflections from boundaries are computed in openPSTD v1.0.
Revision as of 13:36, 10 January 2015
The settings described here correspond to the buttons of the openPSTD v1.0 add-on.
Grid spacing | Max freq
The Grid spacing in metres corresponds to the spacing of the grid points, and is equal in horizontal and vertical direction. The Grid spacing determines the maximum resolved frequency in openPSTD v1.0, i.e. Max freq as follows
with Δ the Grid spacing in metres and c the adiabatic speed of sound. When changing Grid spacing, Max freq automatically changes according to the above equation, and vice versa.
Window size | Patch error
To compute the spatial derivative of the acoustic variables within a subdomain of the drawn geometry, three subdomains are needed, see openPSTD v1.0 overview. The values of the outer subdomains are windowed by a Gaussian window, see Hornikx et al. 2012. The window length applied to the outer subdomains is equal to Window size. This number determines the minimum number of grid points of the subdomains. The window affects the accuracy of the calculation, with the accuracy increasing with the window length. The error introduced by the window is called the Patch error ε in dB, and is defined as:
with p the pressure value at a certain receiver position at a frequency corresponding to 2.5 points per wavelength and the analytical pressure value at this frequency. An ε value of 50 dB corresponds to a level difference error of 0.03 dB. Note that the accuracy of openPSTD v1.0 calculations is not only affected by the window error, but also by the initial source function, the time iteration scheme and the PML layer, see Hornikx et al. 2012. As the error is determined by the maximum error, increasing the window length does not imply that the error is reduced per se. Patch error automatically changes by increasing the Window size, and vice versa.
The simulation length of a calculation in openPSTD v1.0 is denoted by Render time in s. The calculation is terminated after this time. A calculation can also be stopped manually before this time.
When an edge of the constructed configuration is selected, see Getting started with OpenPSTD how to do this, the acoustic absorption coefficient can be assigned to this edge by setting the Absorption to a value between 0 and 1. When an edge is selected, the actual value of the absorption coefficient of this edge is written in parenthesis behind the Absorption setting. In openPSTD v1.0 overview, it is explained how reflections from boundaries are computed in openPSTD v1.0.
The setting Local relates to the absorption coefficient. It the Local box is ticked, the boundary is in approximation treated as a locally reacting boundary. When a reflection free boundary is aimed for, this box should not be ticked.
Pressure level visualisation scale
The Pressure level visualisation scale in dB sets the dynamic range of the relative sound pressure level in the 2D visual animation.
Number of PML cells | Attenuation of PML cels
The Number of PML cells sets the number of grid points in the boundary media that are affected by the perfectly matched layer (PML). The Attenuation of PML cells corresponds to the number α in
with σ the PML damping coefficient, the position of the grid point in the PML layer and D the thickness of the PML layer, see Hornikx et al. 2010. The default value of Attenuation of PML cells is 20000. A larger number of PML cells reduces the error introduced by the PML.
The Density in &kg/m^3; is the density of the propagation medium.
The adiabatic speed of sound of the propagation medium is denoted by Sound speed in m/s.
CFL number RK-scheme
The stability of the calculation is controlled by the CFL number RK-scheme. The default value of this number for the 2D calculations in openPSTD v1.0 is 0.5.
Save every nth
Save every nth sets the interval of discrete time steps used for the visualisation of the 2D results in openPSTD v1.0.
Visualization subsampling sets the interval of discrete spatial steps used for the visualisation of the 2D results in openPSTD v1.0.
The simulation in openPSTD v1.0 is initiated by pressing the simulate with openPSTD button. Before a new run, current results can be cleared by pressing Clear simulation data. During a simulation, the simulation can be termined before the Render time has expired by Stop the current openPSTD simulation.
Bake openPSTD simulation
The computed time dependent 2D sound field can be exported as a movie. The Bake openPSTD simulation command turns the calculations into a movie.