Determining Sponge and Noise Parameters in KTH Framework Example

[Hussein Kokash]

Dear Neks,

I have been looking into the ext_cyl example in the KTH framework that uses both sponge and noise, and I found the following parameters:

[_SPONGEBX]
strength = 1.0
widthlx = 4.0
widthrx = 12.0
droplx = 3.0
droprx = 8.0

[_NOISEBX]
time = 2.0
amplitude = 0.001
boxminx =-5.0
boxminy =-5.0
boxmaxx = 5.0
boxmaxy = 5.0

I would appreciate if you could tell me how I might be able to determine appropriate values for my own simulation case, specifically for sponge parameters `widthlx`, `widthrx`, `droplx`, and `droprx` and for the noise parameters `boxminx`, `boxminy`, `boxmaxx`, and `boxmaxy`, advise on how to adjust these parameters according to the specifics of my simulation?


Thanks!

[Bharathwaj Dharani]

Hi,

If you found the answer for these can you share it with me please. I am working to implement the sponge in my case as well.

Thanks

[Daniele Massaro]

Hi,

Note that these are two different (and not related) modules in the framework (see also HERE).

For the sponge, you just need to set SPONGEBX, where you have the left/right (or top/bottom) extension and forcing parameters.  

The values might be case-dependent.

Kind regards,

Daniele

[Bharathwaj Dharani]

Hello,

Thank you for this. Although I have a few doubts here, can you help me with understanding what these terms really mean. 

[_SPONGEBX]

strength = 100.0

widthlx = 0.2

widthrx = 0.2

droplx = 0.1

droprx = 0.1

from the FRAMEWORK.txt i found a defintion for this although i couldnt make sense of it, 

|spnb_str | real | _spnb:strenght | 0.0 | sponge strength |

|spnb_wl(1) | real | _spnb:widthlx | 0.0 | sponge left section width; dimension X |

|spnb_wl(2) | real | _spnb:widthly | 0.0 | sponge left section width; dimension Y |

|spnb_wl(3) | real | _spnb:widthlz | 0.0 | sponge left section width; dimension Z |

|spnb_wr(1) | real | _spnb:widthrx | 0.0 | sponge right section width; dimension X |

|spnb_wr(2) | real | _spnb:widthry | 0.0 | sponge right section width; dimension Y |

|spnb_wr(3) | real | _spnb:widthrz | 0.0 | sponge right section width; dimension Z |

|spnb_dl(1) | real | _spnb:droplx | 0.0 | sponge left drop/rise section width; dimension X |

|spnb_dl(2) | real | _spnb:droply | 0.0 | sponge left drop/rise section width; dimension Y |

|spnb_dl(3) | real | _spnb:droplz | 0.0 | sponge left drop/rise section width; dimension Z |

|spnb_dr(1) | real | _spnb:droprx | 0.0 | sponge right drop/rise section width; dimension X |

|spnb_dr(2) | real | _spnb:dropry | 0.0 | sponge right drop/rise section width; dimension Y |

|spnb_dr(3) | real | _spnb:droprz | 0.0 | sponge right drop/rise section width; dimension Z |

what does left and right mean, does it mean it will be to the left or right of the whole domain? And I wasnt able to find where the sponge usually initialized, how do i specify the exact coorindates where i need the sponge to be intialised ? or is it the for all BC where I give Outlet BC ' O .

Kindly help me out.

Thank you.

Regards,

Bharathwaj

[Philipp Schlatter]

I recommend to just check in the actual code, that is probably best to figure out what it means.

But in a nutshell: left is low coordinate values, right is high. Width is the size of the sponge, and rise/drop the length of the region where the forcing is smoothly increasing/decreasing.

Philipp

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