[An0n]

Hi all,

I've been running a time dependent simulation of a large mixing vessel and am now looking at using the post-processing particle studies to determine average dwell time.

However, the majority of the particles return the fate 'maximum steps in cell' and get no where near the set maximum length or residence time.

Does anyone know what this fate means? I suspect it may be because the flow is so slow the particles are not moving between cells fast enough (so a finer mesh may provide answers?)

I have another couple of separate but related questions:
- is there away to particle track through the time steps, rather than just looking at a single time step?
- is there a way to smoothly visualise flow trajectories across the time steps? As the geometry I'm analysing is quite complex it is difficult to see what is happening with just cut plots.

Thanks in advance for your help
An0n

[Boris_M]

Hi An0n,

The maximum numbers in a cell means that the solver to calculate the particle's path will stop after a certain time if the particle will not leave the cell anymore, meaning they settled at that location.

No, the particles have moved around a lot until they get stuck somewhere such as a dead corner with little flow to get them out there anymore. You can visualize the particle flow and see where they move.
Either the particles are too heavy to move in the slow flow and simply drop out of it like a rock settles on the bottom of the river while a lighter same sized piece of wood will float along the river, or the flow is too slow to carry the particles along if they have the right weight.
Those maximum iteratons are the ones set in the constraints part of the study definition, just like the time and length you can define the simulation of the particle stops once the finishing criteria is reached.

Not sure I understand your first question with regards to singe time step. The particle study is not an actual transient simulation. Based on the velocity from the flow the particle will have a velocity and move around and depending on its way length, it takes a certain time to leave the model through the outlet. This is all there is related to time.

Also not sure what you mean with your second question.
You can specify the animation time settings but in general, they move all from the inlet to the outlet within the time of the animation. So if you create an animation of 10s then the flow is modeled in the way that everything has left the model in 10s video time.
By extending the time of the video you get a slower movement. But it really depends on what you want to visualize. You can see trajectories with lines or pipes as continues paths showing vortices better but the flow is shown nicer with spheres and arrows as they are moving continuously or are pulsing (depending on the settings). If you want to see what is happening at a certain location, use the trajectories reference in that region such as a surface to see how the flow moves past that surface.

There are many possibilities to visualize the flow depending on what you want to see. Some are good to see movement, others to see flow structures or certain regions of values etc. Animations help to visualize things more dynamically but can also show too many trajectories for example at the same time if they are not wisely defined.

Also you don't have to use the animation recording tool, you can also simply right click on the plot and click the play button to show it live and then you can zoom in and rotate to look at it from all sides. You can also use the "dynamic trajectory" settings instead of the static and then you'll see more arrows or spheres as you zoom in. So instead of having a fixed distance between two arrows along one trajectory, they become more as you zoom in to don't have that gap of data along the trajectory.

I hope this helps,
Boris