Average field on 2D slice

[balcieb]

Hi everyone,

I have a question about calculating an average field on a 2D slice (pseudocolor). Let's assume I have a 3D vorticity dataset for 1000 time steps. I want to find the average y-vorticity field on an xz plane. Can the temporal average be calculated on an xz plane for the y-vorticity field in the VisIt ? Thank you in advance.

[markcmiller86]

Yes.

1. create an expression that represents y-vorticity. Lets call it yv.
2. Do a pseudocolor plot of yv.
3. Add slice operator and orient for y slice (e.g. xz plane)
4. Perform Average value query. That will give the avereage value for that time step.
5. Check the Do Time Query box in the Query window and hit Query button again. Wait a potentially long time for it to iterate over 1000 timesteps. Note, you can adjust start/stop/stride if you want to change performance behavior.
6. Step 5 will produce a second window with a Curve plot of the average value as a function of time.
7. Now, UNcheck the Do Time Query option.
8. Go to the Plot list in the main GUI panel and make the current window 2 and select the Curve plot there.
9. Do the Average value query again on that curve.

The result should be the average over all time of just the y-component.

Am attaching a picture of an example from wave.visit test data. In the attached picture, the GUI panel is showing window 1 selected and you will want window 2 where the Query over time curve plot appears..

[markcmiller86]

Ok. I tried this with wave.visit from our test datasets

First, I created a variable that grows in the x direction, foo, using the expression pressure*sqr(coords(quadmesh)[0]). Then, I created the average-over-time variable, bar, as @biagas recommends above using average_over_time(<foo>). Then I did a Pseudocolor plot of bar (note: when you hit Draw, it may take a long time to render because it will be iterating over all time and computing the average. Then, I applied a slice operator to that Pseudocolor plot of bar. I think that is what @balcieb wants.

[biagas]

If the expression needs to be evaluated on the slice, add the Defer Expression operator after the Slice operator and set the Defer Expression operator's variable to the name of the expression created to do the average_over_time.

[balcieb]

Thank you, @biagas and @markcmiller86 . If the average_over_time expression can give me the 3D region's time average, it is also okay because if I take a slice, the slice will also be time averaged... So, let me try to implement your suggestion on my data.

[balcieb]

Thank you both @markcmiller86, @biagas . I have tried your suggestions. First, I wrote a Python script and, exported the data there and calculated the time average of the 3D field. After that, I followed your instructions and found the time average on the visit. I compared them, and they were matching, so the procedure you suggested works for finding the time average of a 3D field. As a matter of fact, the average_over_time operator works with the box and resample operators, which is really good. Let me summarize what I did to find the time average of 3D field data on the visit:

1. Import your data to visit
2. Create your expression (expression_1)
3. Using avrege_time_over create another expression using the expression_1 (expression_2)
4. Add pseudocolor for your expression_2
5. Add box operator to select the part of the domain you are interested
6. Add a resample operator if your mesh has different levels of refirements
7. Add DeferExpression for expression_1
8. Hit the draw
   If you just want the time average of a slice, you can add a slice operator before adding  DeferExpression for expression_1. As far as I have seen, the time average for a slice is done faster because in the slice case the visit deals with less data points.