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[waves2Foam] A 2D wave tank simulation suffering from wave reflection

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Old   March 22, 2017, 20:27
Default A 2D wave tank simulation suffering from wave reflection
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Gautami Erukulla
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Dear Dr. Jacobsen,

Kindly can you please suggest, a way to simulate a 2D floating body, half submerged at the water surface level, in a wave tank with still water (neutrally buoyant body in still with no initial motion or external forces).

Using waves2foam, I am simulating as follows:

1. relaxationNames (inlet, outlet)
2. initilaizationName inlet
3. inletCoeffs and outletCoeffs are defines as:
waveType potentialCurrent;
U (0 0 0);
Tsoft 0.0;
and relationZones are defined for relaxType INLET and OUTLET

Boundary Conditions: In alpha.water, inlet is type zeroGradient and in U inlet is type fixedValue, value (0 0 0).

The floating box is provided only one degree freedom in y-direction (heave motion). The results show that the box does not approach a stable still position (there is no decay of heave motion).
The results of the same simulation of floating box in still water using interDyFoam, shows that the box approaches a stable still position (decay of heave motion is achieved).
It looks like my simulation approach is not correct kindly please advise. Please do let me know if I was not clear with any information or any additional information needs to be provided. Thank you for your time.

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Old   April 19, 2017, 17:45
Default A 2D wave tank simulation suffering from wave reflection
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Gautami Erukulla
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Dear Dr. Jacobsen,

I have two cases of 3D simulations, the animation of the results show reflection of the waves from the start of outlet relaxation zone. Kindly can you please provide me some guidance regarding this reflection of wave issue.

1. Please find attached, case 1 details in 'boxwavtanksb.pdf' file and its animation for 15s 'boxwavtanksb.ogv'.
2. Please find attached, case 2 details in 'cylinderwavtanksb.pdf' file and its animation for 11s 'cylinderwavtanksb.ogv'. The simulation blows after 11 secs.

Your advise in resolving this issue is immensely helpful. Thank you.

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Gautami Erukulla.
Attached Files
File Type: gz case1sb.tar.gz (186.0 KB, 30 views)
File Type: gz case2sb.tar.gz (140.3 KB, 18 views)
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Old   April 20, 2017, 13:08
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Gautami Erukulla
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Dear Dr. Jacobsen,

Please find attached the 2D wave tank case file where in, the issue of reflection of wave from the start of the outlet relaxation zone is presented.

Thank you for your time and consideration.

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Gautami Erukulla.
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File Type: gz wavTankCasesb.tar.gz (65.8 KB, 30 views)
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Old   April 21, 2017, 10:20
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Gautami Erukulla
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Dear All,

A 2D wave tank simulation suffers from wave reflection from the start of the outlet relaxation zone. There seems a strange pattern of the free surface at the start of outlet relaxation zone. Please find attached the images of alpha, pressure and velocity at the start of outlet relaxation zone.

Details:
Wave Properties: wave height 0.091m, wave period 1.3s and water depth 1m
Mesh: At free surface delta y=0.002, 45 cells per wave height. The entire domain delta x = 0.025, 100 cells per wave length.

I am totally at loss to understand this reflection pattern. Any advise/suggestions in resolving this issue is highly appreciated. Thank you.

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Gautami Erukulla.
Attached Images
File Type: png alphasb.png (11.9 KB, 91 views)
File Type: png pressuresb.png (24.6 KB, 96 views)
File Type: png velocitysb.png (35.2 KB, 84 views)
File Type: png velocitysb1.png (15.0 KB, 59 views)
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Old   April 23, 2017, 11:51
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Niels Gjoel Jacobsen
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Dear Gautami,

You have not shown any convincing data on the reflection, as it seems that you base everything on visual observations. You should perform a reflection analysis based on the surface elevation in a few points. Only in this fashion can you judge the severity of the reflection. This should be done without objects in the NWT.

My paper regarding waves2Foam shows an example of reflection analysis for regular waves and the word by Mansard and Funke (1980) addresses reflection analysis for irregular waves.

Kind regards,

Niels
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Old   July 24, 2019, 08:39
Default Grid Convergence OpenFoam
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Andre White
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Dear Dr. Jacobsen et al:
I am trying to generate a free surface for a 2D wave tank using waves2FOAM. The length of the domain is 10mlong and height is 0.65m. The water depth is 0.5m; depth of air above free surface is 0.15m. The wave height is 0.12m and wave length is 2.82m, wave period is 1.5s. I have used a ppwh of 10 an aspect ratio of 1.
The wave I am using is Stokes2nd. However, there is no good correlation of the free surface for the theoretical and analytical model. @ x=3.3m the numerical model overestimates the value of the wave amplitude; causing it to be greater than the theoretical model.
Can you provide any clarification?

As this is not what I was expecting.
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