# Calculate the step time size

#1

hello, I want to calculate the time step size of my simulation. For this I found the following formula on the internet.
delta_t = beta * (distance between nodes) ^ 2 / thermal conductivity

My problem is finding the distance between the nodes.

Does anyone have some tips or a solution to my problem.

#2

The formula you have quoted is that for the conduction timescale. Is that what you are trying to calculate.? The simulation time step size is something else and you can set it under simulation control. I suppose the conduction time scale is of interest as you would want your time step to be smaller than this this number. Regarding the distance between nodes, i’m not sure that there is any information about the distances (remember that the elements are all sorts of different shapes and sizes) between them but since you can measure distances between edges of your CAD geometry in your CAD package, surely you can print out a screenshot of your mesh, measure with a ruler and then scale accordingly.

#3

I have the formula from this page.
https://caeai.com/blog/calculating-solution-settings-transient-thermal-analysis-part-2

My Biot number is below 1, so I use the first formula.

#4

The time step is an interval that you choose. In the article you linked it says, correctly, that the smaller the time step the more accurate the result but also the more computing resources required. As such the article recommends that you set your time step to equal the conduction timescale (as per the formula) giving you a trade off between accuracy and computing resources.

If you want to use this method then estimate the length of an element near a heat exchange interface (here the elements will be small and the thermal gradient high). After you finish the simulation, rerun it with a smaller time step. If the results are the same it means your time step was already sufficiently small.

#5

Thank you very much for your help. Have a nice day 