[mrzarei]

Hi
I want to use porous media (darcy law) in reef3d, like kamath 2015 paper with application in OWC wave energy converter.
But unfortunately I do not know how and where I should apply it.
I would be so thankful if anyone can help me.

[valgrinda]

Porous media can be invoked by using B 240. In general though, the VRANS option is the more consistent way to calculate flow through porous media. VRANS can be used with options B 260 to B 310. See here for more details: https://reef3d.files.wordpress.com/2...cej_porous.pdf

[mrzarei]

Originally Posted by valgrinda

Porous media can be invoked by using B 240. In general though, the VRANS option is the more consistent way to calculate flow through porous media. VRANS can be used with options B 260 to B 310. See here for more details: https://reef3d.files.wordpress.com/2...cej_porous.pdf

Thank you so much,

I want to validate kamath paper in 2015 about oscillating water column, But unfortunately I have some problems.

In definition of porous media, I defined it at the orifice along with the parameters in the following command. but I have a problem with velocity, velocities exceeding the critical value.
I would be so thankful if you could help me with the definition of porous media location.

B 240 * double Darcy porous media as rectangular box: C;D;xstar t;xend;ystar t;yend;zstar t;zend

[mrzarei]

I want to use Reef3D, Please only refer me to the equation that used for "D" in darcy porous media, B 240.

Unfotunately I can't find it's equation in Reef3D codes.

[valgrinda]

For the OWC, you only use "C" from B240, "D" is zero. The background can be found here: https://reef3d.files.wordpress.com/2..._ijme-2015.pdf - have a look at equations 14 and 15. The other parameters describe the volume where the porous media is active.

In addition to B 240, also use B 241 1. This way, the porous media only impacts the vertical velocity component.

[valgrinda]

The implementation can be found in iowave_velsource.cpp.

[mrzarei]

Thanks a lot

I read both of kamath papers about OWC. He used C as a linear parameter of darcy law, but I want to use D as a nonlinear parameter for validation of an experiment that I read in another paper.

However, if you remember the formula that includes D parameter, please send it to me.

Regards

[valgrinda]

The complete formula is implemented for B 240, including the non-linear part:

porousterm = p->B240_D[n]*a->visc(i,j,k)*a->u(i,j,k) 
       + 0.5*p->B240_C[n]*a->u(i,j,k)*fabs(a->u(i,j,k));

[Varada]

Hi,

I am trying to run a CFD case (OWC with porous media as a turbine) to familiarize myself with the simulations. But unfortunately, there seems to be some error. Can anyone have a look?

A file containing the code and STL file is attached.


Is it because of my STL file?

When I applied porous media on the solid surface of the OWC, the simulation ran well without any errors, but I was not getting airflow through the orifice when I visualized the VTU file in paravew, and the results are also not matching with the published literature. (Do I need to provide porous media on a solid surface or on an orifice?)

I also ran a code by providing a porous media on the orifice, but simulations popped up an error during the reef3d run saying EMERGENCY STOP -- velocities exceeding critical value N 61.

Any help on this matter is appreciated.

Thanks

[mrzarei]

Hi

In reef3D, two parameters of C & D were defined oppositely.
you should write C instead of D and D instead of C.
I checked it and got good results.

Originally Posted by Varada

Hi,

I am trying to run a CFD case (OWC with porous media as a turbine) to familiarize myself with the simulations. But unfortunately, there seems to be some error. Can anyone have a look?

A file containing the code and STL file is attached.


Is it because of my STL file?

When I applied porous media on the solid surface of the OWC, the simulation ran well without any errors, but I was not getting airflow through the orifice when I visualized the VTU file in paravew, and the results are also not matching with the published literature. (Do I need to provide porous media on a solid surface or on an orifice?)

I also ran a code by providing a porous media on the orifice, but simulations popped up an error during the reef3d run saying EMERGENCY STOP -- velocities exceeding critical value N 61.

Any help on this matter is appreciated.

Thanks

[Varada]

I'm having trouble figuring out the permeability coefficient mentioned in the publication by Arun Kamath et al (2015). As you can see from the attached image, they have provided the P and q values, and we are aware of the water's viscosity, but what about the A and L values? How did they arrive at 1/Kp=500000000?

Kamath.JPG

Reference: Kamath, Arun, Bihs, Hans and Arntsen, Øivind A. “Numerical investigations of the hydrodynamics of an oscillating water column device.” Ocean Engineering Vol. 102
(2015): pp. 40–50.

[kamath]

A is the cross sectional area of the nozzle.
L is the length of the nozzle in the direction of travel

[Varada]

Hi Arun,

I am trying to perform a CFD simulation using a cylindrical OWC and compare the pressure and surface elevation results of the experimental data. Although I have successfully validated the wave elevation, I have been unable to validate the pressure fluctuations. The pressure fluctuations that I obtained are ten times smaller than those observed in the experimental data. Any assistance with this issue would be greatly appreciated.

[kamath]

Technically you don't need the porous media to simulate the OWC.
The small cross-section of the opening is what results in the pressure drop.
Given REEF3D offers irregular meshing, I would recommend that you try replicating the OWC as in the experiments and place a higher density of cells in the region near the vent.

In Kamath et al. (2015) that you refer to above, the vent is much larger than the vent in the model tests. The porous media formula is then used to represent the pressure drop that a much smaller vent would provide, while using a much wider vent in the numerical simulation.

It is worth looking into using irregular grids around the vent instead

[Varada]

As you can see from the above attached control and ctrl files I am not using any porous media and at the same time I refined the mesh around the orifice but still unable to validate pressure results. Kindly look at the above attached files and correct my files if required or give me some suggestions to get proper pressure fluctuations.

Thank you

[kamath]

Have you verified that your chosen grid represents the waves correctly (say in a 2D simulation and then optimise)?

Then a 2D simulation with device (a planar slice of your device will be rectangular elements that you can build with the S options in Divemesh) to look at the gridding required to represent the air flow properly.

Is there air flow through the vent in your stl?

I would recommend solving the problem step-by-step, making sure each part is working. In the process you might discover what the problem could be.