P_INIT_POS(p)[i]

February 2, 2009, 05:30

Hello everybody...

Does anybody know the exact meaning of this Macro..?

The explanation in the UDF manual is not quite clear to me.

Do i address to the Cell (position) a particle is in?

I'm writing a UDF, that should give me the position of the Cell my atomizer is currently in (Airblast). Because i'm moving it in space.

I tried it with P_CELL.. and i'm getting weird results.. Thanks...

gera · August 21, 2014, 03:42

Hi Patrick!

Did you find description of P_INIT_POS(p)[i]?
How to use it?

Thank you!

pakk · August 21, 2014, 09:01

P_INIT_POS(p) contains the initial position of particle p.
Initial here means really initial. In the beginning of the simulation. This position will never change during the simulation.

P_POS(p) contains the current position of particle p.
This keeps changing during the calculation because your particle keeps moving.

P_POS0(p) contains the position of the particle where it entered the current cell (mesh cell). If the particle is still in the first cell, it will be the same as P_INIT_POS. Once the particle has traveled to a different cell, P_POS0 will always be located on a cell boundary.

How to use it: that question is unanswerable, it depends on what you want to do. That is like asking "how do I use the number 3". You use P_INIT_POS(p) if you do something for which the initial position of the particle is important. How you use it, depends 100% on your goal.

pakk · August 21, 2014, 09:04

Or, for an easier explanation:

On the 'passport' of a particle:
P_INIT_POS is the birthplace of a particle.
P_POS0 is where the particle last crossed a border.
P_POS is the place where the particle now lives.

gera · August 23, 2014, 08:43

pakk, thank you very much for the detailed explanation! Now, it is clear to me!

February 2, 2009, 05:30	P_INIT_POS(p)[i]	#1
patrick Guest Posts: n/a	Hello everybody... Does anybody know the exact meaning of this Macro..? The explanation in the UDF manual is not quite clear to me. Do i address to the Cell (position) a particle is in? I'm writing a UDF, that should give me the position of the Cell my atomizer is currently in (Airblast). Because i'm moving it in space. I tried it with P_CELL.. and i'm getting weird results.. Thanks...

August 21, 2014, 03:42		#2
gera Member Georgy Join Date: Apr 2011 Location: Russia Posts: 32 Rep Power: 15	Hi Patrick! Did you find description of P_INIT_POS(p)[i]? How to use it? Thank you!

August 21, 2014, 09:01		#3
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	P_INIT_POS(p) contains the initial position of particle p. Initial here means really initial. In the beginning of the simulation. This position will never change during the simulation. P_POS(p) contains the current position of particle p. This keeps changing during the calculation because your particle keeps moving. P_POS0(p) contains the position of the particle where it entered the current cell (mesh cell). If the particle is still in the first cell, it will be the same as P_INIT_POS. Once the particle has traveled to a different cell, P_POS0 will always be located on a cell boundary. How to use it: that question is unanswerable, it depends on what you want to do. That is like asking "how do I use the number 3". You use P_INIT_POS(p) if you do something for which the initial position of the particle is important. How you use it, depends 100% on your goal.

August 21, 2014, 09:04		#4
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	Or, for an easier explanation: On the 'passport' of a particle: P_INIT_POS is the birthplace of a particle. P_POS0 is where the particle last crossed a border. P_POS is the place where the particle now lives.

August 23, 2014, 08:43		#5
gera Member Georgy Join Date: Apr 2011 Location: Russia Posts: 32 Rep Power: 15	pakk, thank you very much for the detailed explanation! Now, it is clear to me!