What is the difference between transient and steady state

I want to solve a nonlinear time dependent forces problem,is it ok to solve it with sol or sol Hello Cyprien, I have a query regarding transient thermal analysis. We have two scenerios here: 1. Need to know temperature of the system after some time, say 30 minutes, however thermal constants such as K thermal conductivity , Convection coefficients are NOT changing with the temperature at all 2.

Thanks for the practical posts, we are watching you Hi Vaibhav, I think it depends on your system. If you think that 30 min is long enough to reach a steady-state temperature temperature is not changing after and you are interested only in the final temperature then a steady-state thermal simulation should be enough.

Now, if your problem is to observe the change of temperature from the very beginning to know what happens to the temperature inside your model at every step and determine precisely when you will reach the steady state in your part equilibrium of temperatures , then you should perform a transient thermal study.

From my knowledge, the fact that thermal coefficients depend or do not depend on temperature do not influence the choice between steady state study of transient study. Only if your coefficients depend also on time…then it would. What is the difference between the transient-state analysis and steady-state analysis of LTI systems? Both A and B. None of the above.

Due to the false-transient scheme used by CFX, technically yes , if you use a very small timestep for both the transient with a first order approach for the time derivative and the steady state simulation, you should arrive at the same result after the same number of timesteps are run in each.

But this also means you're not bypassing the transient solution at all; you're just solving it by other means. Also, this completely defeats the purpose of running a steady-state simulation, which is to fastly arrive at a time independent solution. Glenn Horrocks.

The steady state solver does not include some of the transient terms I forget which, you will have to look up the doco to find that out. Also the steady state solver can advance different equations with different pseudo-timesteps. This is to make the simulation converge faster, but it does mean the result is not time accurate. But these neglected terms are not important for all simulations, and the advancing of different equations at different speeds can be stopped by specifying a physical time step.

Then a steady state simulation will be pretty close to a transient simulation. February 12, , If you use the First Order scheme for the transient equations, there should be no extra terms compared to the steady state equations. It is just for both. The only thing missing on the SS solution will be the transient non-linearities corrections between timesteps, but then again a small enough timestep one that uses only 1 iteration per transient timestep should solve this.

Thanks for that - it's quite insightful. So if I understand correctly you're saying you can make a good comparison between stopping a steady state simulation mid way and a transient simulation using first order numerics for the transient scheme?

A steady state simulation with a very small physical timestep, one that would require only one iteration for the transient solver, yes. But again, that basically means running a transient simulation anyway, so there is no gain in here. Quite the other way, actually: a transient simulation with adaptative timestepping would probably be able to arrive much faster at the desired physical time value. May I ask why do you want to do this?

February 17, , Hi, Thanks for your input. I'm undertaking a project which involves heating a tank of water and modelling the evaporation process from water to vapour.

Sorry I should have explained this much earlier. Edmund Singer P. I would say no. How can you justify the SS solution partway? How it gets there is totally not time accurate if you utilize the SS as it should be used no need to capture the transients. Like brunoc said, trying to get a time accurate solution from a SS run, is probably not efficient. This simulation sounds like one where significantly different time scales are relevant. If that is the case then running it as a full transient will be slow and not very efficient.

The tools that are available for predicting the behavior and conditions of multiphase flow in wells and pipes may be divided into two core categories: correlations and physics-based models. Correlations are relationships between two or more physical variables, generally obtained by curve-fitting to a set of observed data measurements.

This means that correlations may only be applicable for a limited range of systems and conditions. Physics-based models are instead based on fundamental physical principles, like the conservation of mass, energy and momentum.

Here, we can distinguish between steady state physics-based models and transient physics-based models. In practice, many flow simulation tools use a combination of correlations and physics-based models. Physics-based simulation models may use correlations to describe certain phenomena, like bubble and droplet entrainment in multiphase flow or the inflow from a reservoir. Steady state models are based on the assumptions that all flow conditions and properties of the system are constant with respect to time.