[CFD-Henning]

Hello,
I have a question about the wave generation in waves2foam:
Originally I thought, the wave properties (alpha, pressure, orbital velocities etc.) are calculated according to the wave theory and were put as bc. at the inlet boundary. So the waves enter the domain "perfectly" and deform immediately behind the inlet.

My results (see attachement) tell me a different story (visualisation tool by katakgoreng).
It seems, that the waves are not only entering the domain from the left but are also generated by an elevation of the surface in the complete inlet area.
Or do I see this wrong?
This area can be defined in the waveProperties.input-dict, whereby I thought this was just for relaxation of opposite directed waves.

So, how exactly are the waves generated in this inlet area?
And maybe further: If the waves would be deformed in this area (e.g. by fluid-structure-interaction), is there any function underlying, which would pull back these deformed waves to the inital stokes wave in this inlet area? (This is actually the crux of the matter and results directly from the first point.)
Many thanks for any suggestions in advance.

Henning


waveProperties.input:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.OpenFOAM.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      environmentalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

seaLevel 0.844;
seaLevelAsReference    false;

T               1.0;

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

initializationName outlet;

inletCoeffs
{
    // Wave type to be used at boundary "inlet" and in relaxation zone "inlet"
    waveType    stokesSecond;  

    // Water depth at the boundary and in the relaxation zone
    depth       3;

    // Wave period
    period      $T;

    // Ramp time of 2 s
    Tsoft       $T;

    // Phase shift in the wave
    phi         0.000000;

    // Wave number vector, k. 
    direction  (1.0 0.0 0.0);

    // Wave height
    height      0.02;

    debug    no;
    
    // Specifications on the relaxation zone shape and relaxation scheme
    relaxationZone
    {
        relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;
    
        relaxType   INLET;
        startX              ( -2 0 -1.1 );
        endX                ( 5 0  1.1 );
        orientation         ( 1 0 0 );
    }
};

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

    relaxationZone
    {
        relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;    

        relaxType   OUTLET;
        startX              ( 7 0 -1.1 );
        endX                ( 10 0  1.1 );
        orientation         ( 1 0 0 );
    }
};



// ************************************************************************* //

surface elevation:
Solid line: analytical solution
Dashed line: numerical solution

[CFD-Henning]

Hello again,
I've got another bigger issue related to the VOF-method:
By refining the mesh in the shown way, the water level drops briefly in the transition area after starting the simulation:

mesh.png

surface_elevation.gif

I think this could be caused by a difference in the alpha-value of two adjacent cells of different height. Unfortunately the surface is not going completely back to the initial position, so a "pre-simulation" to obtain a new stable initial state seems not to be a perfect solution.
I want to calculate very sensitive cases, so I need a smooth sea surface.

I'm new to OpenFOAM and before I accept this semi-optimal solution, I want to ask, if anybody knows a best-practice way to handle this problem.

[CFD-Henning]

Originally Posted by CFD-Henning

Hello,
I have a question about the wave generation in waves2foam:
Originally I thought, the wave properties (alpha, pressure, orbital velocities etc.) are calculated according to the wave theory and were put as bc. at the inlet boundary. So the waves enter the domain "perfectly" and deform immediately behind the inlet.

My results (see attachement) tell me a different story (visualisation tool by katakgoreng).
It seems, that the waves are not only entering the domain from the left but are also generated by an elevation of the surface in the complete inlet area.
Or do I see this wrong?
This area can be defined in the waveProperties.input-dict, whereby I thought this was just for relaxation of opposite directed waves.

So, how exactly are the waves generated in this inlet area?
And maybe further: If the waves would be deformed in this area (e.g. by fluid-structure-interaction), is there any function underlying, which would pull back these deformed waves to the inital stokes wave in this inlet area? (This is actually the crux of the matter and results directly from the first point.)
Many thanks for any suggestions in advance.

Henning


waveProperties.input:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.OpenFOAM.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      environmentalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

seaLevel 0.844;
seaLevelAsReference    false;

T               1.0;

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

initializationName outlet;

inletCoeffs
{
    // Wave type to be used at boundary "inlet" and in relaxation zone "inlet"
    waveType    stokesSecond;  

    // Water depth at the boundary and in the relaxation zone
    depth       3;

    // Wave period
    period      $T;

    // Ramp time of 2 s
    Tsoft       $T;

    // Phase shift in the wave
    phi         0.000000;

    // Wave number vector, k. 
    direction  (1.0 0.0 0.0);

    // Wave height
    height      0.02;

    debug    no;
    
    // Specifications on the relaxation zone shape and relaxation scheme
    relaxationZone
    {
        relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;
    
        relaxType   INLET;
        startX              ( -2 0 -1.1 );
        endX                ( 5 0  1.1 );
        orientation         ( 1 0 0 );
    }
};

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

    relaxationZone
    {
        relaxationScheme Spatial;
        relaxationShape  Rectangular;
        beachType        Empty;    

        relaxType   OUTLET;
        startX              ( 7 0 -1.1 );
        endX                ( 10 0  1.1 );
        orientation         ( 1 0 0 );
    }
};



// ************************************************************************* //

surface elevation:
Solid line: analytical solution
Dashed line: numerical solution

One quick note to my question: After reading the waves2foam manual, it's obvious, that the weighting function is underlying.

Excuse me for this rash question.