Hello,

Making my own structure and running non-linear elastic static study. I have defined my own stress strain curve and ran my simulations. Adding pressing to certain rectangular area on my structure, I have made 3 tables, each have exactly the same forces/geometry/Material properties, and the only thing changing is the time steps.

Now in each table I have 5 rows, with each row I have changed the mesh size from finest to coarsest. (Attached is a file where it will make all the above easier to understand and see).

In the last column, I have calculated the Force/Load by hand, by multiplying the pressure with the area of the rectangle that I applied it to. I.e I have set the max. time to 5 seconds, expecting the model to fail before it reaches the max. (A column shows the max time step reached).

My two critical questions are:

1- From the maximum time step reached for each mesh, I am calculating that pressure on that certain time. Hence, with each single time-step, a fixed load is considered. Is that correct?

2- Before obtaining my tables, I would have thought with very time the element size is smaller (Finer) a max. step reached would be higher towards the 5 second time set. And should have a consistent Load, either increasing or decreasing. (Shown in the last column). Is it normal being random, or am I calculating it wrong, or something else I am doing, is wrong?

Please, anyone who is sure or have a certain explaintion let me know, as I can not seem to understand the coming results.

Many thanks in advance.

"1- From the maximum time step reached for each mesh, I am calculating that pressure on that certain time. Hence, with each single time-step, a fixed load is considered. Is that correct?"Yes, you load is increased with each pseudo time step. For example, if you had a 100 MPa load, your step size is 0.05 seconds, and your end time is 1 second, then your pressure is increasing by 5 MPa per time step. I'm not too familiar with how SW engine works, but I would imagine that if the solver is having issues reducing the residual norm to an acceptable level, then it would automatically reduce the load factor and trying iterating again.

"Before obtaining my tables, I would have thought with very time the element size is smaller (Finer) a max. step reached would be higher towards the 5 second time set."I don't understand what you're asking here. Is it that you assumed that as the mesh was refined (i.e. element size decreased), that the maximum time step reached would be closer to 5 seconds?

"And should have a consistent Load, either increasing or decreasing. (Shown in the last column). Is it normal being random, or am I calculating it wrong, or something else I am doing, is wrong?"I'm a little confused about your maximum load column. You stated that you, "calculated the Force/Load by hand, by multiplying the pressure with the area of the rectangle that I applied it to." But you also stated that, "each have exactly the same forces/geometry/Material properties, and the only thing changing is the time steps." Can you provide a little more information about how you calculated the maximum load by hand (as opposed to having the solver calculate the reaction load for example).

However, I did notice that your maximum load isn't a random variation; looking at your table you'll see that the higher the maximum time step, the higher the maximum load. Since the load is increased with each increase in the pseudo time steps, you're maximum load will be dependent on your maximum time step.