[Allison]

Hello

I am trying to analyze floating body using reef3d.
I’m confused about X13 Rigid body dynamics representation, What's the difference between X13 1 and X13 2? I find that the Ze(X13 1，REEF3D_6DOF_E_force.dat) is not the same as the Fz (X13 2，REEF3D_6DOF_forces_0.dat), I mean they're all resultant force in z direction of the object. So what's the difference between these two options?

With best regards
Allison

[kamath]

As described in the User Guide,
X 13 1 follows the older implementation for the handling of fluid-floating body interface in REEF3D (Bihs and Kamath, 2017, IJNMF 83 (12), 905-916, doi: 10.1002/fld.4333) using the Ghost cell immersed boundary method.

X 13 2 is the new implementation for the same, using a direct forcing ghost cell method, following Martin et al. 2021, Appl. Oce. Res. 106, doi: 10.1016/j.apor.2020.102410.

[Allison]

Thank you so much , I have read two articles, and I ' m confused about "a direct forcing ghost cell method” following Martin et al. 2021, Appl. Oce. Res. 106. I find in the article, it uses the direct force to deal with fluid-structure interaction, where does the "ghost cell" idea reflect?

With best regards
Allison

[TobiasMartin]

Hi,


as my colleague has already tried to explain, these are two different implementations.



The ghost cell immersed boundary method is described in Bihs and Kamath, 2017, IJNMF 83 (12), 905-916, doi: 10.1002/fld.4333.

It is though recommended to use X 13 2 which is the continuous direct forcing method following Martin et al. 2021, Appl. Oce. Res. 106, doi:10.1016/j.apor.2020.102410. Here, no ghost cells are required.



I hope this helps.


Kind regards,
Tobias

[Allison]

Hi，

Thank you so much ,Now I have a general understanding that these are two different approaches, I used to confused the description about "a direct forcing ghost cell method"
Now I'm trying to learn more about this method

With best regards
Allison