Steady state and transient, and when the difference matters
Choosing between them, and the cost of choosing wrongly.
Steady state and transient are two different questions a simulation can answer, one describing where a system settles once everything has stopped changing and the other describing how it gets there, and choosing the wrong one for a given problem produces a technically correct answer to a question nobody actually needed asked.
Solving for the balance, or marching through time
A steady-state simulation solves for the condition a system reaches once nothing is changing with time any more, ignoring the path taken to get there and computing only the final balance. That is a legitimate and much cheaper shortcut whenever only the settled outcome matters, because the solver has to find one state where everything balances.
A transient simulation solves the same equations at a sequence of time steps, carrying the system forward from one moment to the next and capturing whatever appears briefly before it settles. Resolving a one-minute event in steps of a hundredth of a second means six thousand steps, each with its own full round of iterations and its own saved field to store, which is why steady state stays the default whenever the transient detail is not needed.
A middle ground, called quasi-steady, solves a sequence of steady-state problems one after another, treating the system as if it settles instantly at each new condition. That works while the system reaches its new balance much faster than the conditions around it change, and breaks down once its own response time becomes comparable to how fast those conditions move, which is the regime a true transient solution exists for.
An overnight charge and a fast top-up
Charging a phone overnight, the only thing that matters by morning is the final battery reading, and one check at that point says everything a person needs to know. Charging the same phone quickly during a short stop on a journey is a different case. Held in the hand, the phone can be felt heating up in the first few minutes as the fast charger pushes current in, before the phone's own management settles into a slower, cooler trickle. A single reading at the end of the stop misses the part that mattered most, the heat build-up partway through.
Both are the same physical process at two different speeds, and the speed decides whether a single end reading is enough or whether the whole curve needs watching.
Deciding before the mesh is built
Choosing steady state when the real question was transient throws away the part of the answer that mattered, with no warning from the solver, because a steady-state result never announces the behaviour it was never asked to compute. The choice starts with asking whether the engineering decision depends on the settled state alone or on what happens along the way, and that question belongs before the first cell of the mesh is built. An overnight steady-state study and a week-long transient one can both be correct on their own terms, while only one answers the question the project needed answered.