# transient analysis

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 May 10, 2011, 04:19 transient analysis #1 Senior Member   Govindaraju Join Date: Apr 2010 Posts: 207 Rep Power: 10 Sponsored Links I am doing transient analysis in a branched pipe having different cross sections ( one inlet and two outlets) I assumed the fluid is a non Newtonian. I assumed the central maximum velocity at the inlet is 0.8m/s and the inlet flow is fully developed flow now I want to apply pressure pulse (sinusoidal) at the inlet. Kindly give an idea to set up the boundary conditions. Thank you kmgraju

 May 10, 2011, 14:30 #2 Member   Max Join Date: Apr 2011 Posts: 47 Rep Power: 8 write a profile data with the spatial fields in place and time. import this as user function and use as inlet expression. if its only a mean pulse, just use an expression. EDIT: sorry this was to easy. i assume you already set velocity at the same region? maybe its possible with the user function to use more than one variable. i have never tried it this way

May 10, 2011, 23:55
transient analysis
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Govindaraju
Join Date: Apr 2010
Posts: 207
Rep Power: 10
Quote:
 Originally Posted by max3.2 write a profile data with the spatial fields in place and time. import this as user function and use as inlet expression. if its only a mean pulse, just use an expression. EDIT: sorry this was to easy. i assume you already set velocity at the same region? maybe its possible with the user function to use more than one variable. i have never tried it this way
Dear friend I could not understand .

I am new to this user function.Can you please explain little more.

my velocity equation is :

Umax( 1-r^2/R^2)

I set the above expression in the inlet.

Now I would like to apply a pressure pulse for 1 sec at the same inlet The pressure pulse may be square step function or step sin function for 1 sec

How to set this pressure pulse condition at the inlet again.
What to set in the Global initialization.

Please help me to write user function as you said it was to easy to proceed further.

Thank you

Regards

Govind

 May 11, 2011, 02:18 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 13,647 Rep Power: 105 Are you trying to define both the velocity and pressure at the same boundary? This is not possible. It is mathematically badly-posed. Unless you want to switch from a velocity inlet to a pressure inlet, that can be done (although it is a bit weird and will have convergence problems).

 May 11, 2011, 04:30 #5 Member   Max Join Date: Apr 2011 Posts: 47 Rep Power: 8 Just for the record - to use profile data, build a csv with following header Code: ```[Name] InletBC [Spatial Fields] x,z,t etc.. [Data] x [mm],z [mm], t[s], Velocity[m/s], Total Pressure [Pa] etc.. 1,1,1,10,10000 more data``` and theinclude by tools->initialise profile data in pre. but, as G. Horrocks said, both pressure and velocity is not possible at the same time

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