Background Pressure Field (for Transient Models)

Add a node to model an background/incident pressure wave to study the scattered pressure field ps, which is defined as the difference between the total acoustic pressure pt and the background pressure field pb:

This feature sets up the equations in a so-called scattered field formulation where the dependent variable is the scattered field p = ps. In a model where the background pressure field is not defined on all acoustic domains (or it is different), continuity is automatically applied in the total field pt on interior boundaries between domains.

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For enter a value for the p0 of the wave, select the as (enter a value for c) or , enter a vector ek, enter the f0 of the wave, and a possible

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For enter a value for the p0 of the wave, select the as (enter a value for c) or , enter a vector ek and enter the x0. The latter two options define the initial location of the pulse and the propagation direction. When modeling scattering problems, the initial location should be placed outside the computational domain. Next define the frequency content of the Gaussian pulse. Select the as (the default), , , , or . For the first two options enter a frequency bandwidth Δf and for the latter a time window Δt. Finally, enter the carrier f0.

where the standard deviation σ of the Gaussian G(x,t) depends on the bandwidth option selected. The modulated Gaussian pulse option only gives contributions when a time dependent model is solved. It has the advantage of having a defined frequency content and can be used for limited bandwidth simulations. In combination with the Exterior Field Calculation (for Transient Models) and an FFT study, the broadband scattering characteristics of an object can be analyzed.

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For enter an analytical expression that can be a function of both space and time or use a solution from a previous study.

To display this section, when the option is selected, click the button (

) and select in the dialog box

Click to select the option (selected per default). With this option turned on, a ramp is automatically added to smoothly increase the background pressure field amplitude over the first period T = 1/f0. This option ensures numerical stability.