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Unable to get the proper heave response of a floating barge facing head wave

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Old   September 15, 2020, 07:44
Exclamation Unable to get the proper heave response of a floating barge facing head wave
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Smith
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Hello everyone,

I am trying to get the heave response of a floating barge facing head wave (1st order) for quite sometime now. I tried many different modelling and tuning of the factors involved in the process. The simulation has one problem. It is now giving the heave response about zero mean. It is always going upwards (as shown in the figure). I contacted the local support office but they could not help me to get through it.

Domain dimensions: Lx = 12m, Ly=5m, Lz=5m
Brge dimenion: Lx=3.0m, Ly=0.4m, Lz=0.3m and draft = 0.1m
(The CoG of the barge at [0,0,0] of the domain)
1st Edit: Barge has only heave and pitch motion. Pitch time series included in the post.

Any help I will appreciate.
Attached Images
File Type: jpg Barge_heave_response.JPG (110.7 KB, 7 views)
File Type: jpg barge_pitch_response.JPG (122.0 KB, 3 views)

Last edited by sumitkpal; September 17, 2020 at 23:00.
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Old   September 17, 2020, 03:24
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this could be a number of things:

if you also have rotation motion about y freed for the barge then plot this and see how stable this motion is since it will affect the heave. i assume you have locked z rotation.

it could be wave reflections of two types in the x direction, more likely from the outlet so implement wave damping and also maybe slowly coarsen up the mesh in the wave refinement towards the outlet boundary but make your domain longer in the x direction.

there also might be reflection from the barge back to the inlet and back again and so you should use wave forcing to reduce this effect - both explained at this help topic: Simulating Physics > Multiphase Flow > Modeling VOF Waves > VOF Wave Forcing and Wave Damping
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Old   September 17, 2020, 23:09
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Quote:
Originally Posted by ping View Post
this could be a number of things:

if you also have rotation motion about y freed for the barge then plot this and see how stable this motion is since it will affect the heave. i assume you have locked z rotation.

it could be wave reflections of two types in the x direction, more likely from the outlet so implement wave damping and also maybe slowly coarsen up the mesh in the wave refinement towards the outlet boundary but make your domain longer in the x direction.

there also might be reflection from the barge back to the inlet and back again and so you should use wave forcing to reduce this effect - both explained at this help topic: Simulating Physics > Multiphase Flow > Modeling VOF Waves > VOF Wave Forcing and Wave Damping
Thank you for your reply. For the first point, I attached the pitch motion figure newly to the post and it can be seen that it is quite stable.

Second point and third point: I am already using the VOF wave forcing option for inlet and outlets. But the mesh is not slowly coarsened up towards the outlet bounday as of now. I used the finer and uniform mesh towards the outlet. I can change and let you know about this. I will update the result soon with comparison to longer domain and updated mesh.

Thank you so much.
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barge, dfbi, head-wave, multiphase flow

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