sediment transport: can't notice any diffraction behind the brakewater
 

Dear friends



My name is Giannis. I m undertaking my PhD thesis in hydraulic departure of civil engineering school of Aristotle University of Thessaloníki, Greece. My thesis deals with sediment transport for the protection of the coastline. Mr. Karampas is my supervisor. For the time being I am using the magnificent program waves2Foam to simulate the wave field. I started from 2D simulations and now I execute 3D applications. I am sending you an image (I have also the animation available) via paraview. My problem is that I can't notice any diffraction behind the brakewater. Why does this happen???? I can't imagine. I took care of wave parameters and the length of the brakewater. I used blockMesh tool for for meshing, and the mesh was just perfect. I am sending also o snapshot. The dimensions of the breakwater is 10m x 5m x5m and the wave period is about 3 seconds. With a wave height of 0.5 m. The depth of the field is constant at 3m.
I also include the files of wave parameters and the characteristic of the mesh



below its the link of the animation in dropbox

Attachment 53613

Attachment 53616

Attachment 53617

Attachment 53618

Attachment 53619

https://www.dropbox.com/sh/qwqbcvqhs...FG3IuACua?dl=0

Hi Kazakis,

It is an interesting problem. I do not understand that you do not see diffraction, as it should naturally happen. Maybe your domain is too short or you expect to see too large a response in the lee of the breakwater.

At least, I have already looked at diffraction in the past, see pp. 76-78 of my thesis (http://orbit.dtu.dk/en/publications/...05b7ff01).html). The results are not perfect, but it does show a qualitatively correct behaviour.

Kind regards,

Niels

Dear Niels

Thank you for your reply. For a deeper look i prepared one more case.Certainly the is a problem! I am sending you some snapshots and the input files. I cant imagine where the problem is! maybe the blockmesh tool i used instead of snappyhexmesh? maybe the input wave? maybe the courant number?? the vectors of the velocity are totally wrong! Whats your opinion?

Kind regards

Giannis

Also the input files

Dear friends,


The fact that I expand a 2D case into 3D probably has to do with the lack of diffraction?
(I used the solvers and the setup from beji battjes case). I would be grateful if anybody could provide any opinion for that, and also to suggest a 3D case to start from (maybe 3D waves?)


Kind regards
Giannis Kazakis

Good afternoon,

@Giannis: You should try to make a comparison with analytical solutions, because the diffraction effect is hard to verify by looking at the wave field. Use wave gauges and perform case specific verification/post-processing. From the pictures you show, it is not a priori possible to say, what the problem is.

Kind regards,

Niels

Dr. Jacobsen


Thank you once more for your reply. I will follow your advices but my primal fear is that the vectors of the velocity are straight ahead. The are not changing direction after the breakwater. I can't explain that phenomenon. Certainly I make something wrong. But i don't know what is this. Finally, I used 3Dwaves. I saw a wave height in the lee of the breakwater but once more the vector aren't changing direction.

I will let you know in case i find the solution

Thank you once more

Kind Regards
Giannis

Dear friends

According to simulation problems of the diffraction, i let you know that the problem has been solved. waves2Foam is able to simulate diffraction properly. Now it's time to compare with analytical solutions. My fault was the boundary conditions of the domain. For the history i am sending you a snapshot of the simulation.

Kind regards