What are the differences between ABS_P(p[c], op_pres) and ABS_P(p[c]) ?

SJSW · March 23, 2017, 00:10

Hi~

I found ABS_P(p[c], op_pres) in the example of DEFINE_CAVITATION_RATE in ANSYS Help.

Then I found ABS_P(p[c]) in the description above :
If ABS_P < p_vapor, then
c_evap * rhoV[c] * sqrt(2.0/3.0*rhoL[c]) * ABS(p_vapor - ABS_P(p[c]))

1. What are the differences between ABS_P(p[c], op_pres) and ABS_P(p[c]) ?
2. What is op_pres?

Thanks!

pakk · March 23, 2017, 02:42

The first part ("If ABS_P < p_vapor, then ... ABS_P(p[c])") from the Fluent help is not really UDF code, but is an explanation of what the goal is, but they wrote the equation already in programming code.

But they obviously made a mistake: ABS_P(p[c]) means the absolute pressure, but they forgot op_pres. In the code below, they did not make this mistake.

"op_pres" means operating pressure.

I am happy that you asked this question: until now I used

Code:

RP_Get_Float("operating-pressure")

to obtain the operating pressure in my UDFs. But now I see that I could just use op_pres, which should make my code more simple (and a tiny bit faster, but I don't think I will notice that).

March 23, 2017, 00:10	What are the differences between ABS_P(p[c], op_pres) and ABS_P(p[c]) ?	#1
SJSW Senior Member Join Date: Jun 2014 Location: Taiwan Posts: 100 Rep Power: 11	Hi~ I found ABS_P(p[c], op_pres) in the example of DEFINE_CAVITATION_RATE in ANSYS Help. Then I found ABS_P(p[c]) in the description above : If ABS_P < p_vapor, then c_evap * rhoV[c] * sqrt(2.0/3.0rhoL[c]) ABS(p_vapor - ABS_P(p[c])) 1. What are the differences between ABS_P(p[c], op_pres) and ABS_P(p[c]) ? 2. What is op_pres? Thanks!

March 23, 2017, 02:42		#2
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 26	The first part ("If ABS_P < p_vapor, then ... ABS_P(p[c])") from the Fluent help is not really UDF code, but is an explanation of what the goal is, but they wrote the equation already in programming code. But they obviously made a mistake: ABS_P(p[c]) means the absolute pressure, but they forgot op_pres. In the code below, they did not make this mistake. "op_pres" means operating pressure. I am happy that you asked this question: until now I used Code: RP_Get_Float("operating-pressure") to obtain the operating pressure in my UDFs. But now I see that I could just use op_pres, which should make my code more simple (and a tiny bit faster, but I don't think I will notice that). SJSW and souza.emer like this.