[Ahmed Elhanafi]

Please click the link below where you can find a paper hopefully solving this problem.http://ecite.utas.edu.au/110364


Thanks,
Ahmed

[pawl]

Originally Posted by ghorrocks

Firstly, have you confirmed you have a situation where the waves are not highly damped?

If the flow should not be highly damped but the simulation is then you have a problem with numerical dissipation. Have you done all the normal things to reduce numerical dissipation? Finer mesh, smaller time steps, high order space and time differencing. Also check the options for the free surface model as some of them are dissipative.

for 14x0.7m tank, 0.381m free surface, 0.1m wave height, I tried dx= 0.005m, dy= 0.01m, and dt=0.005 sec, wave height decreased.
Do I need do finer mesh and timestep?

Originally Posted by Ahmed Elhanafi

Please click the link below where you can find a paper hopefully solving this problem.http://ecite.utas.edu.au/110364


Thanks,
Ahmed

Okey. I already requested that paper. Hopefully your institution accept that qucikly

[Ahmed Elhanafi]

Thanks Pawl,You should get it now. Please feel free to email me in case you still have problems.
Thanks,
Ahmed

[pawl]

Originally Posted by Ahmed Elhanafi

Thanks Pawl,You should get it now. Please feel free to email me in case you still have problems.
Thanks,
Ahmed

email sent...
hopeful I can use your advice to finish my thesis

[ghorrocks]

for 14x0.7m tank, 0.381m free surface, 0.1m wave height, I tried dx= 0.005m, dy= 0.01m, and dt=0.005 sec, wave height decreased.
Do I need do finer mesh and timestep?

If changes in settings affects the results this shows either the mesh is not fine enough or the time step is not small enough. You need to do a sensitivity study to find how fine your mesh needs to be before it does not affect the results, and likewise for the time step size.

[miladzabihi]

I am using ansys v16.0 for wave generation simulation in a 2D numerical wave tank (x=50m *y=5m). A fixed float structure is located at the distance of 30m from the wave boundary condition. The problem is as follows:
whenever I implement a turbulence model (k-e RNG), the free surface elevation starts to be damped after about 90s simulation and after about 200s the wave height decreases drastically. however, when using laminar mode, I dont have this problem. Do you have any suggestion to solve my problem?

[ghorrocks]

That is what turbulence models do, they model the extra dissipation from turbulence effects. Please post an image of the results of the model and what you expect to see. Do you have good experimental data to compare to?

[miladzabihi]

Dear Glenn
As it is shown in the attached pic, you can see a dissipation of wave height during the simulation time. the pic shows surface elevation for a point (6.3meters far from the floating structure) during the simulation time. after about 90s simulation you can see that the waves start to be damped. However in experimental results you cant see this issue.
the model is 2D. wave height 0.22m and T=2s.
when I use laminar model you cant see dissipation.

On the other hand, it should be mentioned that I have already modeled wave tank without presence of the structure and could get good results both in laminar and turbulence models. in brief, I think that existence of the structure causes this damping and from available experimental results, I know that my simulation is wrong now.
Thanks a lot.

[ghorrocks]

I also note that your simulation is using Fluent. For details on Fluent try the Fluent forum. This is the cfx forum.