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transiet analysis error when applied more than 10 s

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Old   June 11, 2009, 02:07
Default transiet analysis error when applied more than 10 s
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muhammad irham mahfud
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hi guys,

I have problem, when i applied more than 10 s for transient analysis error occurred. if you have solution or advice please share to me.. it will helpful

thanks in advance
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Old   June 11, 2009, 07:35
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Glenn Horrocks
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Here's my advice - explain what you are trying to do and what error you are getting. Put the output file on the forum as an attachment. Then we have some chance of being of help.

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Old   June 11, 2009, 11:55
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Quote:
Originally Posted by ghorrocks View Post
Here's my advice - explain what you are trying to do and what error you are getting. Put the output file on the forum as an attachment. Then we have some chance of being of help.

Glenn Horrocks
Hi Glenn,

I want to know pressure rise in cryogenic storage system (vessel) cause heat flux in the system. i applied multiphase fluid (liquid nitrogen and air ideal gas). i attached the out file. this setting work when i applied time duration:10 s.

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File Type: zip 70 10 jam_001.zip (5.6 KB, 7 views)
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Old   June 11, 2009, 12:59
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if I was simulating a cryogenics storage system and I was interested in the heat flux propagation within the system I would use the nasa polynomials for the involved fluids

didnt check the physics thoroughly yet but mesh expansion is 1199.8 ! - have you checked the mesh quality?
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Old   June 11, 2009, 19:42
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Hi,

Nobody has time to do detailed analysis of your simulation, especially a multiphase simulation. But I have noticed the error is divergence of the linear solver - this simply means your simulation diverged big-time. My comments:

1) Start with a simple simulation and add the physics one bit at a time. If you start with the full complicated thing it will never converge.
2) George's comment about mesh quality is important - that may be causing the convergence problem.
3) The documentation has lots of suggestions about getting convergence. Try a smaller initial timestep, double precision, a better initial guess (maybe run a steady state model first) are all things to look at.

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Old   June 11, 2009, 21:21
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First, i want to say thanks to you guys,its very helpful. i am new comer using CFD programs.
one more question, does CFX capable to solve evaporation without flow? as i know CFX based on navier stoke equation.

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Old   June 12, 2009, 03:39
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you will have flow just it wont be forced (buoyancy)
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Old   June 16, 2009, 23:00
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do you have other tips for evaporation in the closed system? i attach again my last result..

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Old   July 15, 2009, 00:12
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Quote:
Originally Posted by ckleanth View Post
if I was simulating a cryogenics storage system and I was interested in the heat flux propagation within the system I would use the nasa polynomials for the involved fluids

didnt check the physics thoroughly yet but mesh expansion is 1199.8 ! - have you checked the mesh quality?
can you give me good materi about nasa polynomials?, thanks
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Old   July 15, 2009, 03:51
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nasa polynomials are polynomials that people use to model the energy state of a particular fluid/gas (cp, enthalpy, entropy) at elevated or subcool temperatures. there are two versions i think the older one with the seven coefficients (the one that cfx uses) is mainly for temps between 200[K]-5000[K] for more information check the nist website and prof Burcat website to check for data in the subcooled range.
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