Learning Forum

[JxBx]

Hey everybody,

for my research i am currently developing a 3d numerical wave tank in ls dyna based on the ALE method. Now I would like to validate the model and compare it with an analytical solution for a wave. How is it possible to get the surface elevation at the water surface ? Is there some kind of sensor or wave gauge?

Thanks!

[ido]

Hello JxBx,

You may try *DATABASE_TRACER and define dummy (floating) nodes at the interface of air and water. Note this interface tracking may not work perfectly because it simply allow the tracers to ride along with the mat vel. At the interface there are 2 materials & this mat mixing makes it hard to track the vel. Sometimes a tracer may get left behind. If you define a few to test you will see how it works.

Ian Do

[JxBx]

Hello Ian,

thank you for your answer. I already tried the tracer option, but the problem is, as you said, that the dummies move with the fluid (they have a movement in x-direction). This is not the case with a wave gauge, which measures the wave elevation at a fixed point.

Another solution that occurred to me would be to determine the wave elevation for the volume of fraction for the material water. Is it possible to obtain the volume fraction for certain points? 

 

Thank you,

Jonas

[ido]

Hi Jonas,

I have an idea which I have not tested before and not sure it'll work. But you can try setting up a small dummy example to see. Maybe you can try to constrained the tracers' motion with BOUNDARY_SPC_SET, then fix the DOFs in the other 2 dir, and allow freedom only in the vertical dir? Let me know if that works.

Ian

[JxBx]

Hi Ian,

i tested your idea, but unfortunately it is not working well. The tracer is still moving in x-direction (with the wave), even though i have this movement constrained. I found a method using the volume of fraction in this paper (https://lsdyna.ansys.com/wp-content/uploads/sites/2/2022/12/validation-of-the-ale-methodology-by-comparison-with-the-experimental-data-obtained-from-a-sloshing-tank.pdf). 

If you have another solution, I am happy about any further help.

Jonas

[ido]

 Hi Jonas,

Do you have a small example showing that you can send me. I can look into it. I suspect that it may or may not work. Some additional development may be needed. We are totally swamped right now so I can't promise anything. If you can find a work-around, pls do that. It'll take some time before we can sort this out.

Ian

 

[JxBx]

Hello Ian,

 

I sent you an email because I could not send the file in this forum.

Jonas

[Caleb Wood]

Hi JxBx,

I ran into this same issue quite some time ago and still haven't found a solution to it. For me, the best next thing was to create a shell element spanning the length of the tank at the height of the expected wave and then verifying it visually (do not assign any contacts to the element, just use it as a reference guide). Obviously it does not give an exact answer but if you are verifiying your results against a paper you should be able to tweak it over several iterations to get a match.

On a side note, do you mind telling me the EOS along with the values you are using for water? This is something I have been struggling with for quite some time now.