Question about flight time histogram plotter

[wangpengfy (wang peng)]

Hello All,
I want to use histogram plotter got flight time before molecular get absorbored.But the plot seems strange to me.

In my understanding,the y-axis should represent probobility.The probability should not keep increasing as the flight time decreases; that doesn’t seem right. My understanding is that the probability of flight time should reach a maximum at some point.

If the y-axis doesn’t represent probability, please let me know what it does represent.

Wishing you health and well-being.

[maarton (Marton Ady)]

The plot shows the absorption moment. As you chose “Global”, it denotes the whole system (so any sticking facet increments the plot).

Most likely your injection point also has a sticking, allowing very small flight times as particles return after a single bounce. For example, with Test menu / Quick Pipe, max recorded time 1ms, bin size 1E-5s:

Disabling the sticking on the inlet, you indeed see a maximum:

[rkerseva (Roberto Kersevan)]

Hello: I wanted to reply to your previous message here, but I see that you have deleted it.
I read the paper on the Sensors journal, but unfortunately the authors do not explain well enough their geometry, the different figures and the text give contradictory explanations.
They claim they calculate tau, the diffusion time, but they don’t say how they define it.

Coming to this message, the Histogram plot is NOT a probability plot, in fact it is eithe “Absolute” values, i.e. proportional to the number of hits (and therefore increasing as the simulation is left running), or “Normalized” to the highest value (to remove the running time dependency of the “Absolute” scale). If you want to visualize the probability distribution then you need to copy the data, past it into (for instance) Excel, and normalize each value to the running sum of the distribution, easy to do. There is no built-in probability visualization plot in Molflow+.

[wangpengfy (wang peng)]

Hello Marton
I’m very happy that you can reply.It seems I already disable sticking on the inlet.

And it still not appear maximum pointl.This is my model,hope you can find problem.
xureview1mm.zip (4.2 MB)

[wangpengfy (wang peng)]

Hello Roberto,
I’m glad you could reply.The reason why i delete previous message,is I think I found a way to simulate the diffusion time.

I understood the article as the author setting one face as an outlet while the remaining faces act as reflecting walls. Then, the author sets the adhesion coefficient at the outlet to be 1. This way, gas molecules reaching the outlet are considered to escape. I believe the author also obtained the average escape time for different slit widths through histograms.

Using my model as an example, I set the four narrow sides of a rectangular prism as outlets, with an adhesion coefficient of 1. One wide side serves as the outlet surface to study the time it takes for gas molecules to escape through the slit.

xureview.zip (507.0 KB)

Returning to the question, to obtain the probability corresponding to each flight time, I processed the data imported into Origin as shown in the figure below. Would the results obtained after this processing represent the probability corresponding to each flight time?

I also attach my model, and I hope you can give me some suggestions.

[maarton (Marton Ady)]

Your sides are all sticking, so indeed the s~0 flight path is most probable.

Those particles that are forced to do a long random walk are less probable then those that get stuck to the side near immediately.

By the way, your histogram plotter cannot plot all values, as the warning message tells.

[maarton (Marton Ady)]

Here is your experiment reworked to only desorb from the center:

Now the flight time has a maximum, since immediate escape through the sticking walls is not possible:

File:
xu_center_desorb.zip (68.9 KB)

[wangpengfy (wang peng)]

Hello marton，
thanks for update my model.Now i know why there is no maximum point.But still have few confusions

1st，Roberto mentioned that the normalized axes do not indicate the probability corresponding to each escape time, so I’d like to know specifically what the normalized values represent.

2nd is the absolute value of the histogram’s vertical axis indicating how many particles correspond to each flight time?

As for the issue of the maximum number of particles being only 1000, I have solved it in the ImG mode, where more particles can be counted.

[maarton (Marton Ady)]

1. Each value divided by the maximal (so maximal bin value becomes 1).
2. Yes, number of monte carlo absorptions recorded for that bin.

[wangpengfy (wang peng)]

Thanks Marton!

About normalized plotter，it seems not divided by maximal value as the plotter provided by you previous. It has some different with what you said “maximal bin value becomes 1”

Best Regard

[maarton (Marton Ady)]

Isn’t it normalizing to the overrange bin, not visible in your image?

Look top right.

				case 1: { //Normalized
					double yMax = 0.0;
					size_t plotLimit = std::min(histogramValues->size(), (size_t)1000);
					for (size_t i = 0; i < plotLimit; i++) {
						yMax = std::max(yMax, (*histogramValues)[i]);
					}
					double scaleY = 1.0 / yMax; //Multiplication is faster than division (unless compiler optimizes this away)
					for (size_t i = 0; i < plotLimit; i++) {
						v->Add((double)i*xSpacing, (*histogramValues)[i]*scaleY);
					}
					break;
				}

The code above selects the maximum value among the first 1000 and divides all values by it.

[wangpengfy (wang peng)]

Thanks soooooo much Marton!
Now I understand histogram plotter.It’s very kind of you spent a lot time explain it for me.
Hope you have great days and years.