Learning Forum

[Emerson Buitrago]

I generated a wave in a tank wave, but now I want to plot time history of wave elevation at a specified position to be able to determine the wave height. I read on the CFX forum that the CEL to use on a Plane is:

areaInt(Water.Volume Fraction)@Area Region/area()@Area Region

This doesn't seems to work with Fluent. Can anyone help me with how to navigate this problem? Thank you.

[Rob]

Have a look on here, I've posted regarding this a few times. Depth is probably a good keyword. There may also be something in the "Search Knowledge" too. 

[Emerson Buitrago]

[Emerson Buitrago]

I have reviewed your posts, but I am still struggling to fully understand, could you provide a more detailed explanation? I am attaching images of my progress, but I am not sure if I am approaching the situation correctly.

Initially, I created an isosurface 2 with a variable x with a value of 0m. Then, I proceeded to create an iso-clip 1 as shown in the image. Subsequently, I generated the expression "minVal(y)@Iso clip 1" with the intention of using it to create the plot.

Could you please confirm if my approach is correct or provide additional guidance on how to approach this problem more effectively? I appreciate your help.

[Rob]

OK, you're in CFD Post, I'd post process in Fluent most of the time now. 

OK, you've got the iso-surface on a plane, x=0.  On that plane create an iso-clip of VOF=0.5 (ish, it's a guide). That should leave you with a surface that's at x=0 and is "wet". Report the max y (or z) on that isosurface, minus the mean water level.  If you need a more specific location for the wave you can clip the x=0 surface by z (or y) to give a smaller zone to check. 

[Emerson Buitrago]

hello, now I have a mishap.
I already have the data of my simulation but it does not give me similarities with one that is my guide, I try to change things but I can't find what I expected, I don't know if you could help me. 
this is my graph 

[Emerson Buitrago]

I see my graph and as time goes by the wave is damping, but in the graph that I'm guiding this does not happen, so I would not know what to change.
this is the other graph

I feel that the problem lies in this section of ansys.

suddenly if I modify the damping factors 

[Rob]

What happens suddenly if you modify damping factors?  Given the value for starting point, can you check you're trying to damp the correct coordinate range?

[Emerson Buitrago]

I was guided by the text of the article where I am being guided and it says this: "The lengths of the CFD simulation domain and wave damping region are more than 7 and 1.5 times that of the wavelength, respectively."

[Rob]

Yes, but you're adding the damping factor at about one wave length into the domain. What happens if you alter any of the values? You also need a reasonable amount of domain that's not damped. 

[Emerson Buitrago]

I'm going to change the star point to 5m and see what happens. 

[Emerson Buitrago]

Hello
I have finished the wave simulation, now I'm working on a similar one. 
It is a device that moves with the waves (I use dynamic mesh) but I get a lot this message of "Floating point exception" usually when that happens to me I decrease the Time Step and it is solved (sometimes), but I do not think it is the right solution or if so? So that's why I want you to see how my meshing looks like
maximum skewness value: 0,56
Minimum orthogonal: 0.68

[Rob]

Please follow this thread  /forum/forums/topic/cfd-floating/  

[Emerson Buitrago]

Hello,
I have done everything but I still can't, but when I initialize in flat if it leaves but it doesn't work like that, I need it in wavy.
any advice?

[Rob]

Waves would come from the inlet condition, I'd initialise the domain as flat as it's easier. 

[Emerson Buitrago]

I thought the same thing but in flat I don't like the model where I'm going to be guided.

[Rob]

Sorry, I don't understand the question. Please can you rephrase it?

[Emerson Buitrago]

I want to obtain the vertical displacement of a buoy in a wave channel, but if I initialize it in flato I can't get the results like that graph in the first 6 seconds, and in the document they initialized it with wavy.
but for some reason whenever I initialize in wavy I get "floating point exception".
the graph I sent is the results I should get.
i have already changed the mesh but i still can't.:/ 

[Rob]

Where did you put the buoy relative to the free surface? Floating point errors tend to be associated with the solver not converging, and having the buoy partially submerged may result in it trying to regain it's neutral position too quickly. 

[Emerson Buitrago]

i have my buoy on the free surface (is submerged 150mm), look like this 

[Emerson Buitrago]

already with the initialized wavy would be submerged 190mm

[Rob]

You may need a smaller timestep to get the model started, or to initialise from a flat free surface and then wait for the waves to develop. 

[Emerson Buitrago]

I was able to solve the problem but now I get the graph like this, and it does not look like the one in the article, I think about increasing the mesh but I do not think it will change that much.

[Rob]

Depending on how long you let the model run that could be reflection from the downstream end of the domain or just the wave not propagating (lack of time or it's being damped). 

[Alfonsa Benedict]

Dear Emerson

So I'm here to ask more about your method. Did you use 2d model to simulate? If yes, what was the expression you input when you want to plot wave elevation? I'm a bit lost on this one, kindly asking for insights. Thank you in advance