x,y,z,t- Dependent Pressure Initialization Using CEL

KeganLeckness · March 26, 2015, 13:51

Hi all,

I'm a graduate student simulating pressure propagation through the ear. I've used an Opening boundary condition at the inlet of the ear canal and
if(t>0.0 [s] && t<0.003 [s], (-6666.6666666666666666666666667 [kPa/s] * t) +20 [kPa], 0.0 [Pa])
to initialize the pressure.

The problem I'm having is due to an artificial wall at the Opening. Although the manuals state that the Opening BC does not add artificial walls like the Outlet or Inlet BCs do, it appears that the Opening condition does add a wall when a pressure like the one above is set at the location of the Opening. I get the negative reflected pressure, as discussed in the description of the artificial walls inherent in Outlet and Inlet conditions. I want to get away from this.

I've tried to implement the beta-feature Acoustic Reflectivity, but this is not applicable. I've also tried to separate a domain for pressure initialization, but this only applies the pressure for t=0 and not t=0 to t=3 ms as desired.

I wish to add spacial constraints to the time constraint listed in the above IF statement so that I may apply this pressure at various locations in the canal's domain. I've read the various guides discussing CCL, CEL, Expressions, Functions, and Routines, but I am having a difficult time understanding and putting it all together.

Would someone be kind enough to elucidate the relationship between the aforementioned topics and tell me what I need to define a pressure depending on x,y,z,&t? If I need to use a library, please explain the purpose of that, too.

I greatly appreciate any assistance,
Kegan

ghorrocks · March 26, 2015, 16:56

There are several options for pressure openings. I was not aware that any of them generated walls to stop reverse flow. So if you are having problems with the boundary condition you are using I would consider changing to a different type. For instance there is opening pressure and direction versus Static pressure and direction, and there is entrainment. Try a few combinations of these.

The problem with all these approaches is that they are going to reflect pressure waves and generate spurious waves. I would investigate the non-reflecting boundary condition beta feature. I would also investigate moving the opening boundary away from the area of interest so the reflected waves do not reach the region of interest (or at least are minimised).

March 26, 2015, 13:51	x,y,z,t- Dependent Pressure Initialization Using CEL	#1
KeganLeckness Member Kegan Leckness Join Date: Mar 2015 Posts: 38 Rep Power: 11	Hi all, I'm a graduate student simulating pressure propagation through the ear. I've used an Opening boundary condition at the inlet of the ear canal and if(t>0.0 [s] && t<0.003 [s], (-6666.6666666666666666666666667 [kPa/s] * t) +20 [kPa], 0.0 [Pa]) to initialize the pressure. The problem I'm having is due to an artificial wall at the Opening. Although the manuals state that the Opening BC does not add artificial walls like the Outlet or Inlet BCs do, it appears that the Opening condition does add a wall when a pressure like the one above is set at the location of the Opening. I get the negative reflected pressure, as discussed in the description of the artificial walls inherent in Outlet and Inlet conditions. I want to get away from this. I've tried to implement the beta-feature Acoustic Reflectivity, but this is not applicable. I've also tried to separate a domain for pressure initialization, but this only applies the pressure for t=0 and not t=0 to t=3 ms as desired. I wish to add spacial constraints to the time constraint listed in the above IF statement so that I may apply this pressure at various locations in the canal's domain. I've read the various guides discussing CCL, CEL, Expressions, Functions, and Routines, but I am having a difficult time understanding and putting it all together. Would someone be kind enough to elucidate the relationship between the aforementioned topics and tell me what I need to define a pressure depending on x,y,z,&t? If I need to use a library, please explain the purpose of that, too. I greatly appreciate any assistance, Kegan

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March 26, 2015, 16:56		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	There are several options for pressure openings. I was not aware that any of them generated walls to stop reverse flow. So if you are having problems with the boundary condition you are using I would consider changing to a different type. For instance there is opening pressure and direction versus Static pressure and direction, and there is entrainment. Try a few combinations of these. The problem with all these approaches is that they are going to reflect pressure waves and generate spurious waves. I would investigate the non-reflecting boundary condition beta feature. I would also investigate moving the opening boundary away from the area of interest so the reflected waves do not reach the region of interest (or at least are minimised).