Transient Simulation in ANSYS CFX

tomide · June 10, 2014, 14:23

please i am trying to simulate hydrate formation in a subsea pipeline system. i have tried to model the flow to the best of my ability but i am having issues with the transient time step flow setting.

i am trying to simulate a flow in a pipe such that the pressure is kept constant and the temperature is reduced gradually. please how to set the time step such that the temperature only changes after every complete run (meaning a molecule of the gas moves from the inlet to the outlet before the temperature changes).

thank you.

ghorrocks · June 10, 2014, 19:09

Your simlation sounds strange. If you are doing a transient model then your temperature should follow the temperature versus time curve. If you are doing a series of separate conditions a steady state simulation is a better way of doing it rather than a transient simulation.

tomide · June 11, 2014, 19:00

thank you very much.. i ran a steady state flow instead.

shooter · June 16, 2014, 15:36

Hi,

I'm very interested in this area. Can you please describe the simulation setup for hydrate formation. are you using UDF??

Thanks!!

tomide · June 16, 2014, 20:30

i am trying to replicate a published experimental set up where hydrate was formed but i am using ansys cfx. right now i am having issues with the solver. keeps telling me error.

----------------------------------
Error in subroutine FNDVAR :
Error finding variable DENSAT_FL1
GETVAR originally called by subroutine cal_DIAM

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

Details of error:-
----------------
Error detected by routine MAKDIR
CDRNAM = cal_IPTC
CRESLT = OLD

Current Directory : /FLOW/SOLUTION/TSTEP5/CLOOP1/ZN1/VERTICES

ghorrocks · June 16, 2014, 21:40

Have you defined all necessary material properties? I suspect you need to define some saturation conditions - maybe the density, and possibly linked to a bubble/nucleation diameter or something like that.

tomide · June 17, 2014, 11:44

@glenn yes i have specified all the material properties needed. i am trying to use the droplet phase change for one of the fluid but i noticed that if i changed the fluid to a dispersed fluid and input a mean diameter the solver doesnt give any error but the problem is that i want to use the droplet phase change cause i want a nucleation to occur in the pipeline. please help me if you can. thanks

June 10, 2014, 14:23	Transient Simulation in ANSYS CFX	#1
tomide New Member Join Date: May 2014 Posts: 7 Rep Power: 11	please i am trying to simulate hydrate formation in a subsea pipeline system. i have tried to model the flow to the best of my ability but i am having issues with the transient time step flow setting. i am trying to simulate a flow in a pipe such that the pressure is kept constant and the temperature is reduced gradually. please how to set the time step such that the temperature only changes after every complete run (meaning a molecule of the gas moves from the inlet to the outlet before the temperature changes). thank you.

June 16, 2014, 20:30	please help	#5
tomide New Member Join Date: May 2014 Posts: 7 Rep Power: 11	i am trying to replicate a published experimental set up where hydrate was formed but i am using ansys cfx. right now i am having issues with the solver. keeps telling me error. ---------------------------------- Error in subroutine FNDVAR : Error finding variable DENSAT_FL1 GETVAR originally called by subroutine cal_DIAM +--------------------------------------------------------------------+ \| Writing crash recovery file \| +--------------------------------------------------------------------+ Details of error:- ---------------- Error detected by routine MAKDIR CDRNAM = cal_IPTC CRESLT = OLD Current Directory : /FLOW/SOLUTION/TSTEP5/CLOOP1/ZN1/VERTICES

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June 10, 2014, 19:09		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Your simlation sounds strange. If you are doing a transient model then your temperature should follow the temperature versus time curve. If you are doing a series of separate conditions a steady state simulation is a better way of doing it rather than a transient simulation.

June 11, 2014, 19:00		#3
tomide New Member Join Date: May 2014 Posts: 7 Rep Power: 11	thank you very much.. i ran a steady state flow instead.

June 16, 2014, 15:36		#4
shooter New Member Damith Join Date: May 2013 Posts: 3 Rep Power: 12	Hi, I'm very interested in this area. Can you please describe the simulation setup for hydrate formation. are you using UDF?? Thanks!!

June 16, 2014, 21:40		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Have you defined all necessary material properties? I suspect you need to define some saturation conditions - maybe the density, and possibly linked to a bubble/nucleation diameter or something like that.

June 17, 2014, 11:44		#7
tomide New Member Join Date: May 2014 Posts: 7 Rep Power: 11	@glenn yes i have specified all the material properties needed. i am trying to use the droplet phase change for one of the fluid but i noticed that if i changed the fluid to a dispersed fluid and input a mean diameter the solver doesnt give any error but the problem is that i want to use the droplet phase change cause i want a nucleation to occur in the pipeline. please help me if you can. thanks