[jatin1990]

hi , i am scratching my head , as how this analysis could be steady state (https://www.youtube.com/watch?v=zyZljNT5n_M#t=351). How its become steady state analysis as he can play the animation of the analysis which is nothing but showing the picture of the temperature profile at different time value, then how its steady state analysis? As far i know steady state do not have to deal with time, so we can,t see the variation of the temperature profile with respect to time, but in this video user is playing an animation of the case study which is playing on a timeline.

Thanks for clarification.

[agd]

My guess is that he is showing the development of the steady state solution. You can reach a steady state by solving the full time varying equations. It just means the unsteady term eventually goes to zero because everything else balances.

[jatin1990]

Originally Posted by agd

My guess is that he is showing the development of the steady state solution. You can reach a steady state by solving the full time varying equations. It just means the unsteady term eventually goes to zero because everything else balances.

Hmm, thanks for reply sir. It's now making sense to me. Why people are talking like steady state even while using transient analysis.

Sir can you clear my doubts regarding steady state analysis, as if we go with a steady state analysis of any quantity of interest then for the initial period of time(this period could be as small as 1 micro second or as big as lets say 1 day), the problem have to behave like a transient problem until equilibrium is not achieved then after that period the equilibrium is reached and steady state is observed. Now my question is how Ansys gets to know that is the steady state is achieved lets show the result to my user. Or my view point is completely wrong for understanding it.

Thank you so much.

[agd]

There are two methods for performing a steady state computation. The first is to solve the steady form of whatever equation set you are interested in. Historically this approach was used because it is less computationally intensive. But if the unsteady equations actually govern the physics, then even steady solutions should arise if the boundary conditions/source terms allow for a solution that tends to steady behavior as time increases. This approach is used more commonly today, because the unsteady solver can then handle steady flows as well as unsteady flows, and computers are much more powerful. How do we know when we've reached steady state (assuming one exists)? The same way we would know in a physical experiment - have the quantities of interest stopped changing with time? Monitor a parameter of interest and examine its behavior.

[virendra_p]

Well answered! Sir Mr. agd

[jatin1990]

Originally Posted by agd

There are two methods for performing a steady state computation. The first is to solve the steady form of whatever equation set you are interested in. Historically this approach was used because it is less computationally intensive. But if the unsteady equations actually govern the physics, then even steady solutions should arise if the boundary conditions/source terms allow for a solution that tends to steady behavior as time increases. This approach is used more commonly today, because the unsteady solver can then handle steady flows as well as unsteady flows, and computers are much more powerful. How do we know when we've reached steady state (assuming one exists)? The same way we would know in a physical experiment - have the quantities of interest stopped changing with time? Monitor a parameter of interest and examine its behavior.

That was a great piece of information sir. Please help me with below points:

1.Does this mean for a given problem , the steady state analysis will give an error while computation , if the problem under investigation does not have a steady state at all?

2. What will be the error message in that case in Ansys?

3. Is the error shown in point 1 is sole cause of the Divergence of the solution?

4. If yes to 3 , then can we say every inability to find steady state(performed in a steady state analysis module) will cause Divergence but every Divergence situation is not derived by non steady situation(there may be other reasons of divergence also).
5. If there may be other reasons of divergence , please ponit some of them here.


Thank you So much agd sir.

[agd]

1. A steady solver may return a nice looking, completely wrong result even the actual behavior is unsteady. Understanding the physics involved is essential. There may be no error flags.
2. I don't use ansys so I have no idea what error messages it may yield. But you may not get any. You may get a result that looks nice but is wrong. See point 1.
3. No. See above. The solution may not diverge. The solver may give a reasonable looking solution until you consider the underlying physics. Or your problem may have a steady solution and you get a diverging result because your grid is bad or your boundary conditions are poorly implemented or your iteration step is too big or there is a bug in the code or...
4. No.
5. See 3. There are any number of reasons why solvers diverge. If you are using a commercial code I recommend looking for tutorials on problems similar to yours and studying them in as much detail as possible. Try to learn the significance of all the inputs and how to evaluate the outputs from a physical understanding.