Acoustic simulation with high frequency (ex. 1 MHz)
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Hi Montanaro! Thank you for your reply.
Could I reduce the computational size by adding a wire block around the focal region voxelized with max cell size suitable for 1MHz (0.15 mm) and the rest of the domain coarser (0.3 mm) ? Does it provide sufficiently accurate results according to your experience? -
Hi Annalisa, you should definitely have at least the minimum suitable grid size everywhere in your simulation (should correspond to default grid setting if I remember correctly).
This corresponds to the material with slowest speed of sound / frequency and then some multiple of this (number of grid points per minimum wavelength) ... Do you by any chance have air in your simulation? maybe replace this with water if that's ok?
Unfortunately, high frequency acoustic simulations require large grid sizes and there aren't many ways around that..
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Unfortunately, I am working with a asymmetrical transducer and also Duke is not really symmetrical !
Transducer and Duke are embedded in water. The only air in my computational domain is represented by the internal air in Duke head.
So no chance for the moment.
Thank you in any case -
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This is correct but if there is any air in that area you should remove it. The maximum grid step is calculated by looking at all the materials in the simulation and finding the one with the lowest speed of sound (air, around 300 m/s, everything else should be around 1500 m/s except for bone which is higher), and then dividing that by the simulation frequency (and some factor indicating minimum number of grid points per wavelength).
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But when I remove the head from the grid settings, the material considered for automatic calculation of the max cell step is water (in my case, f=500 kHz, so max step = 0.3 mm). So, I suppose that in voxeling the module takes into account this cell size as the maximum. Correct?
I also tried to include the head in my simulation in order to see the difference in the grid. In this case, the automatic setting for the whole head becomes 2 mm, but in both cases I have the same total number of cells. It seems that the module considers a fixed voxelization of Duke head. That could be possible? -
I'm not sure, but the elements in the grid settings define the size of the grid and also where some grid lines should definitely be (the red lines in the grid). The actual resolution should be calculated based on the materials in the whole simulation domain within the total grid.
Did you mean to say that your default grid settings went from 0.3 mm to 2 mm?
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I usually change the automatic settings in manual (by including the transducer and the water background and removing Duke): max step 0.3, resolution 0.45 and priority 0. In that way, all the objects in my manual settings (transducer and water background) are set at 0.3 mm. Then in voxeling I include also Duke, but in this way I don't know what is the step used for voxelizing the head.
If I include the head object also in gridding automatically S4L set its cells at 2 mm as maximum size, and the rest of the domain at 0.3 mm.
Both cases result in the same total number of cells in the whole computational domain.
For answering your question: when I include also the head as a grid object, the automatic grid settings of the ONLY head are automatically set at 2 mm (with no action by myself). -
Oh I see, but if you use manual grid settings then you should really be careful that the resolution is fine enough. I would suggest making some tests: make your resolution finer and see how much your results change. Hopefully they don't change much (maybe within a few percent).
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Moving to manual settings, I kept the same step and resolution as the default automatic values. I only changed the priority from 50 to 0 in order to remove the red lines and reduce the number of cells I had. (that was a suggestion from a colleague of mine). Anyway, I will make some tests. Thank you for your suggestions.
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