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how to make the negative pressure as zero in surface intergration 

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September 1, 2015, 02:20 
how to make the negative pressure as zero in surface intergration

#1 
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Join Date: Apr 2015
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i work on hydrodynamic fluid bearings. here due to cavitation of fluid i observe negative pressure. when i calculate the surface integrals for the load carrying capacity, the negative pressure is also integrated.
can you please suggest me how can i make the negative pressure as zero in the calculation of the surface integrals?? it should also be zero when i calculate the mid plane pressure plot. i have attached a mid plane pressure plot. you can see that the curves reach negative pressures too. i want that to be neglected, i.e, zero as it is my boundary condition. please help. 

September 1, 2015, 02:27 

#2 
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September 1, 2015, 09:57 

#3 
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it looks like some coding work. can i just not do it using the software abd some tools in it??


September 1, 2015, 16:38 

#4 
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Lucky Tran
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I'm not familiar with the cavitation model but isn't the absolute static pressure clipped at 0 anyway? You have a negative absolute pressure or gauge pressure? A negative gauge pressure should be acceptable is it not?


September 2, 2015, 04:11 

#5 
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I agree with what LuckyTran said, in my experience the absolute pressure is never below zero...
But to literally answer your question, you can always output results to a text file and read that in matlab, octave, excel or your favourite analysis tool, and set the negative values to zero, and do the integral calculation yourself. 

September 2, 2015, 10:17 

#6 
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yes i have put reference frame as absolute and the gauge pressure is zero.
i have attached an image wer u can see the negative pressure devloped. i need that part to be zero. its the fluid part. how can i do that???? how can i integrate values in excel???? please help. 

September 2, 2015, 10:55 

#7 
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Andrew Kokemoor
Join Date: Aug 2013
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This is pretty easy in CFDPost. If you make an expression for positive only pressure:
Code:
max(0[Pa],Pressure) Code:
areaInt_x(PosPressure)@surface 

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