Difference between transient analysis and static analysis with time steps

[matparta]

Hello
I am not so used to working in the time domain, hence this question.
What is the difference between doing a transient structural analysis and a static analysis with time steps, where the external load is indeed applied in different time steps?

I have seen the following situation. A transient thermal analysis is performed on a structure. The distribution of temperatures as function of time is loaded into a static structural analysis. Such static structural is run at all the time steps of the thermal one and the thermal load on the structure is accordingly changing at each time steps.

So
- why this combination of transient and static?
- why not running transient thermal and transient static?

Cheers

 

[driftLimiter]

I picture it this way. A static analysis with time steps really is just a series of static analysis. For each given time step you have a given loading and a given displacement that are un related to any other time steps.

When you say 'transient' analysis I take that to mean what is often called a dynamic analysis. For example if you apply a starting displacement or load to a structure at t=0. You want to know what happens to the structure at each time step after the load is released.

 

[matparta]

Yes, I mean dynamic analysis in the time domain (ie not dynamic in the frequency domain). I am just using the language that eg Ansys is using calling such analyses as transient.
In my example - the thermal transient analysis gives the temperature distribution as load for the time steps -> the structural response is given by the thermal load at those time steps. Hence, with a series of static analyses at same time steps as the thermal analyses then I know what happens to the structure at each time step given by the load. What would be the difference with a transient structural analysis?

 

[IRstuff]

Atransient analysis solves partial differential equations that govern the heat spread in materials for time and distance. Static analysis will only show the result at t=infinity and will not reflect the transient movement of heat.

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[swimfar]

A static analysis is one where your boundary conditions are not changing, and your solution is not changing. It's also generally assumed that the BCs were applied slowly.
A transient analysis just means things are changing over time, and you probably care about the solution at multiple time states. A transient analysis could be caused by your boundary conditions changing (applied loads change over time). Though, for CFD analyses you can get transient solutions from constant boundary conditions.
A dynamic analysis is a transient analysis that takes inertia into account (i.e., moving mass). If you're trying to accelerate something quickly, or if things are vibrating, or your time scale is such that the propagation speed of loads through your structure is important, you need to run a dynamic analysis.

Sometimes you may run a quasi-static analysis which uses multiple time steps to apply a load slowly in order to find the solution to a static analysis problem. The advantage of doing this is that for non-linear (e.g. large deformation) problems it's sometimes easier for implicit codes to find the solution by breaking it up into smaller steps. This technique is also used if you're running an explicit code, which always breaks problems up into (tiny) time steps.

It's not clear to me where thermal vs. structural come into play in your question. But the distinction between static and transient is the same for both.