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[waves2Foam] Velocities are far lower than what I am expecting

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Old   July 13, 2016, 08:11
Default Velocities are far lower than what I am expecting
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ArielJ
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Hi everyone,

I've been running waveFoam for a while but in an effort to understand OF and CFD so from a beginners view. I have just realised that my velocities are far lower than what I am expecting. I am using a potentialCurrent with U (0.5 0 0), to simulate flow around a cylinder, so I expect to see velocities around 0.5, but instead my velocities in the section after my relaxation zones are closer to 0.1 (or lower) and then immediately behind the cylinder they jump up to the 0.3 range, before increasing again to around 0.5 in the outlet relaxation zone (see screenshot of clip).

My waveProperties.input file looks like the following:

Code:
seaLevel	0.00;

// A list of the relaxation zones in the simulation. The parameters are given
// in <name>Coeffs below.
relaxationNames (inlet outlet);

initializationName outlet;

//pName		   p_rgh;
inletCoeffs
{
    waveType        potentialCurrent;
    U               ( 0.5 0 0 );
    Tsoft           0;
    //waveType		stokesFirst;       	// Regular waves
    //depth		25; 			// Water Depth 
    //period		8;	 		// Wave period
    //phi			0.00000;		// Phase
    //direction		(1.0 0.0 0.0);		// Direction of incoming waves
    //height		1.5;			// Wave height in meters
   
    
    relaxationZone
    {
	relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;
    
        relaxType   INLET;
        startX      (-160 -80  0.0);
        endX        (-100  80  0.0);
        orientation      (1.0 0.0 0.0);
    }
};




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

    relaxationZone
    {
        relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;    

        relaxType   OUTLET;
        startX      (180 -80    0.0);
        endX        (240  80    0.0);
        orientation      (1.0 0.0 0.0);
    }
};


// ************************************************************************* //
Any ideas on this? Maybe my relaxation zones are a problem?

Thanks in advance everyone!
Attached Images
File Type: png screenshot_U.png (37.1 KB, 31 views)
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Old   August 17, 2016, 08:35
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ArielJ
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Hi there,

I posted a question earlier about the very low velocities that I'm seeing but I've also noticed that the surface elevation does not maintain the input level. Has anyone had or solved an issue to do with a quickly dampening surface elevation? I have attached a snapshot of the surface elevation along the length of the tank. This is for a tank that is approximately 10*L long and each relaxation zone is approximately 1.5*L.


*EDIT* - I just compared two simulations for a linear wave, one with both inlet and outlet relaxation zones and one with inlet only. The outlet relaxation zone is affecting the surface elevation far away from it... How can I fix this so it only damps out but doesn't affect it further up the domain??

QUESTION 2: I am trying to validate another simulation which uses a 25 m long wavelength in a domain that is only 8 metres long. How would I adjust the relaxation zones to keep the domain size the same? Is this possible?

Last edited by arieljeds; August 23, 2016 at 08:32. Reason: added another example image, free surface elevation problems
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Old   January 4, 2021, 19:57
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Arun Kumar
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Quote:
Originally Posted by arieljeds View Post
Hi there,

I posted a question earlier about the very low velocities that I'm seeing but I've also noticed that the surface elevation does not maintain the input level. Has anyone had or solved an issue to do with a quickly dampening surface elevation? I have attached a snapshot of the surface elevation along the length of the tank. This is for a tank that is approximately 10*L long and each relaxation zone is approximately 1.5*L.


*EDIT* - I just compared two simulations for a linear wave, one with both inlet and outlet relaxation zones and one with inlet only. The outlet relaxation zone is affecting the surface elevation far away from it... How can I fix this so it only damps out but doesn't affect it further up the domain??

QUESTION 2: I am trying to validate another simulation which uses a 25 m long wavelength in a domain that is only 8 metres long. How would I adjust the relaxation zones to keep the domain size the same? Is this possible?

Hello Ariel,
I know that the post is quite old, but did you happen to find the reason behind this change in velocity? I am also trying to create an ONLY-Current scenario in my 2D wave tank. Like you, I am using potentialCurrent to generate a current (of 0.25 m/s) at the inlet. Please let me know if you have found a solution to this problem of reduced current velocity in the domain.
Thanks,
Arun.
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