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[waves2Foam] free surface elevation seems to decrease as the distance from the inlet

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Old   September 19, 2016, 11:56
Default free surface elevation seems to decrease as the distance from the inlet
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Gautami Erukulla
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Dear Dr. Jacobsen,
I am experiencing a similar issue as Mr. Ariel. The free surface elevation (wave elevation) seems to decrease as the distance from the inlet increases. The following are the main details of the simulation case.
Geometry and Mesh Details:
Wave Tank : Length 30m in x direction and height 0.8m in y direction.
Water depth: 0.6m
Number of cell in horizontal x direction: 600 (0.05 cell size and its 31 cells per wave length)
Number of cell in vertical y direction: 400 (0.002 cell size and its 10 cells per wave height)
Wave Properties:
relaxationNames (inlet outlet);
initializationName outlet;
inletCoeffs
{
waveType stokesFirst;
Tsoft 1;
depth 0.600000;
period 1.0;
phi 0.000000;
direction (1.0 0.0 0.0);
height 0.02;

relaxationZone
{
relaxationScheme Spatial;
relaxationShape Rectangular;
beachType Empty;
relaxType INLET;
startX (0 0.0 -1);
endX (13 0.0 1);
orientation (1.0 0.0 0.0);
}
};



outletCoeffs
{
waveType potentialCurrent;
U (0 0 0);
Tsoft 1;

relaxationZone
{
relaxationScheme Spatial;
relaxationShape Rectangular;
beachType Empty;
relaxType OUTLET;
startX (18 0.0 -1);
endX (30 0.0 1);
orientation (1.0 0.0 0.0);
}
};



Results:
The wave elevation within the inlet relaxation zone shows good results with crest and trough amplitude of 0.01m. After the relaxation zone (i.e. in the free computational domain) the wave amplitude drops to 0.008m and it drops further down the domain. There is no problem with the wave period. Changing the waveType to stokesSecond did not resolve the issue. Please let me know if this has something to do with the way the relaxation zones are defined. Kindly can you guide me in resolving this issue. Excuse me if this has already been answered in one of the previous threads. Thank you for your time.
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Gautami Erukulla.

Last edited by wyldckat; August 25, 2018 at 09:05. Reason: added link to the other thread
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Old   September 19, 2016, 16:36
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P { margin-bottom: 0.08in; page-break-before: auto; }A:link { } Dear Dr. Jacobsen,
I am writing again with more information in regard to the issue that I posted earlier (#1302). Was able to successfully simulate and validate a case as discussed and presented in the following link (Case 1):
http://www.cfd-online.com/Forums/ope...topics-27.html (#525)
Details of Case1 (from the above link):
Wave Properties:
waveType stokesFirst;
Tsoft 2;
depth 0.4;
period 2.0;
phi 0.000000;
direction (1.0 0.0 0.0);
height 0.01;
Geometry and Mesh Details:
Wave Tank : Length 18 m in x direction and height 0.6 m in y direction.
Water depth: 0.4 m
Number of cell in horizontal x direction: 360 (0.05 m cell size)
Number of cell in vertical y direction: 60 (0.01 m cell size)
Relaxation Zones (Inlet, Outlet):
relaxType INLET;
startX (0 0.0 -1);
endX (5 0.0 1);
orientation (1.0 0.0 0.0);
relaxType OUTLET;
startX (13 0.0 -1);
endX (18 0.0 1);
orientation (1.0 0.0 0.0);
The results of this case 1 are presented in the following figures at 3 different locations in the domain.
waveElevation6msb.png -- at 6 m from Inlet
waveElevation9msb.png -- at 9 m from Inlet
waveElevation14msb.png -- at 14 m from Inlet
There seem to be a good agreement with the analytical results.



CASE 2:
Geometry and Mesh Details:
Wave Tank : Length 30 m in x direction and height 0.8 m in y direction.
Water depth: 0.6 m
Number of cell in horizontal x direction: 600 (0.05 m cell size)
Number of cell in vertical y direction: 80 (0.01 m cell size)
Wave Properties:
waveType stokesFirst;
Tsoft 1;
depth 0.600000;
period 1.0;
phi 0.000000;
direction (1.0 0.0 0.0);
height 0.02;
relaxationZones (Inlet, Outlet)
relaxType INLET;
startX (0 0.0 -1);
endX (10 0.0 1);
orientation (1.0 0.0 0.0);
relaxType OUTLET;
startX (20 0.0 -1);
endX (30 0.0 1);
orientation (1.0 0.0 0.0);
The results are presented in the following figures, at 4 different locations in the domain.
Case2WaveElevation5msb.png -- at 5 m from Inlet
Case2WaveElevation10msb.png -- at 10 m from Inlet
Case2WaveElevation15msb.png -- at 15 m from Inlet
Case2WaveElevation20msb.png -- at 20 m from Inlet
The wave elevation decreases as the distance from the inlet increases. Kindly can you please guide in resolving this issue. Please let me know if any additional data or information needs to be presented. Thank you for your time and consideration.


Case2sb.zip

Resultsb.zip



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Case2sb.zip

Resultsb.zip
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Old   September 19, 2016, 16:43
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P { margin-bottom: 0.08in; page-break-before: auto; }A:link { } Dear Dr. Jacobsen,
I apologize, forgot to mention in my earlier post that:
The results, image files are presented in the 'Resultsb.zip' folder and the case set up is presented in 'Case2sb.zip' folder. Sorry for any trouble caused. Your guidance is invaluable. Thank you.
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Old   September 19, 2016, 17:22
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Hi Gautami,

It is simple. You are using to few points per wave length.

Kind regards,

Niels
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Old   September 19, 2016, 17:54
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Gautami Erukulla
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Dear Dr. Jacobson,

Thank you very much for your reply. Will set up a case with increased number of points per wavelength. I shall keep you posted. Thanks again

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Old   September 20, 2016, 10:19
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P { margin-bottom: 0.08in; page-break-before: auto; }A:link { } Dear Dr. Jacobsen,


I have simulated a case with increased number of points per wave length as the details are:
Geometry and Mesh Details:
Wave Tank : Length 30 m in x direction and height 0.8 m in y direction.
Water depth: 0.6 m
Number of cell in horizontal x direction: 1600 (0.01875 m cell size and approximately 81 cells per wave length )
Number of cell in vertical y direction: 300 (0.00267 m cell size and approximately 7 cells per wave height)



Wave Properties ( No Change):
waveType stokesFirst;
Tsoft 1;
depth 0.600000;
period 1.0;
phi 0.000000;
direction (1.0 0.0 0.0);
height 0.02;



relaxationZones (Inlet, Outlet) (No Change)
relaxType INLET;
startX (0 0.0 -1);
endX (10 0.0 1);
orientation (1.0 0.0 0.0);
relaxType OUTLET;
startX (20 0.0 -1);
endX (30 0.0 1);
orientation (1.0 0.0 0.0);
I am still facing the same problem of decrease in wave elevation as the distance from the inlet increases. Please find attached the results presented in the following figures:
waveElevation9msb.png -- at 9 m from Inlet
waveElevation14msb.png -- at 14 m from Inlet
waveElevation16msb.png -- at 16 m from Inlet
waveElevation19msb.png -- at 19 m from Inlet
Your insights on these results will be immensely helpful. Kindly please advise. Thank you for your time.
Note: Please find case file attached
WaveElevation9msb.png

WaveElevation14msb.png

WaveElevation16msb.png

WaveElevation19msb.png

finemeshcasesb.zip
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Old   September 20, 2016, 12:55
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@Gautami: From what I see, your results improve with improved resolution. I would hence suggest a mesh sensitivity study.

Kind regards,

Niels
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Last edited by wyldckat; August 25, 2018 at 08:53. Reason: removed answers to other posts that were on the main thread
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Old   September 20, 2016, 16:10
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Dear Dr. Jacobsen,

Thank you very much for your guidance, will work on it and keep you posted .

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Old   October 7, 2016, 14:25
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P { margin-bottom: 0.08in; } Dear case1sb.pdf

x0to4m.png

x4tp7m.png

x6to10m.png

waveElevatinAt4p5m.png Dr. Jacobsen,



As per your advise I have refined the mesh and was able to obtain results in good agreement with the analytical solution. Please find attached a pdf file 'case1sb.pdf' where in the results are presented. Thank you for your help .


Currently I am working on another case and facing a different issue, the details are:



Geometry and Mesh Details:
Wave Tank : Length 12 m in x direction and height 2 m in y direction.
Water depth: 1.4 m
110 cells per wave length and 50cells per wave height

Wave Properties
waveType stokesSecond;
Tsoft 0;
depth 1.4;
period 1.132;
phi 0.000000;
direction (1.0 0.0 0.0);
height 0.1;


As the distance from the inlet is increased, there is a phase shift in the wave elevation plot. I have considered two simulations with different relaxation zones as :


Simualtion-1 (Rz_2In6Out)
relaxationZones (Inlet, Outlet)
relaxType INLET;
startX (0 0.0 -1);
endX (2 0.0 1);
orientation (1.0 0.0 0.0);
relaxType OUTLET;
startX (6 0.0 -1);
endX (12 0.0 1);
orientation (1.0 0.0 0.0);



Simulation-2 (Rz_4In4Out)
relaxationZones (Inlet, Outlet)
relaxType INLET;
startX (0 0.0 -1);
endX (
4 0.0 1);
orientation (1.0 0.0 0.0);
relaxType OUTLET;
startX (
8 0.0 -1);
endX (
12 0.0 1);
orientation (1.0 0.0 0.0);



Attached are the plots of results.Your guidance in resolving this issue will be invaluable. Kindly please advise. Thank you for your time.


X0to4m.png: shows wave pattern at time 20s from inlet to 4 m of wave tank.
X4to7m.png: shows wave pattern at time 20s for 4m to 7m of wave tank.
X6to10m.png: shows wave pattern at time 20s for 4m to 7m of wave tank.
WaveElevationAt4p5m: shows wave elevation w.r.t time at 4.5m.


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