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Floating Body Simulations

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Old   June 8, 2021, 13:46
Question Floating Body Simulations
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Will
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Hello, I am still fairly new to the world of numerical modeling, and I am wanting to employ REEF3D to simulate the hydrodynamics of a simple, floating cylinder breakwater. Is there any available tutorial for a floating body simulation, as to this point, I have not found anything and am struggling to make progress. All simulations up to now have experienced the same problems of exceeding the critical velocities and the cylindrical body beginning to free-fall well outside of the domain.

Any advice and direction is greatly appreciated!
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Old   June 9, 2021, 06:25
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Ali Burhan
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Hello Will,

I am also trying to analyze floating body using reef3d.
The following options worked for me. For control.txt file:

Quote:
C 11 1
C 12 3
C 13 3
C 14 2
C 15 3
C 16 3

B 1 0.1
B 10 0 20 0 40 0 3

B 101 11
B 127 0.1 0.5 9 6 1.05
B 102 11
B 128 0.1 0.5 20 4.0 1.05
B 103 11
B 129 0.1 0.5 2.20 0.7 1.05

B 130 1

M 20 2
M 10 12
For ctrl.txt file:

Quote:
B 10 1 use wall functions for the velocities
B 11 1 use wall functions for the turbulence model
B 20 2 slip or no-slip boundary conditions for velocities no slip
B 50 0.000045 wall roughness for steel
B 60 1 turn on ioflow
B 61 1

D 10 4
D 20 2 implicit

F 30 3
F 40 3
F 50 1 fix level set for inlet
F 60 2.20370 initial free surface level

I 10 1

M 10 12

N 40 2
N 45 5000000
N 47 0.3

P 10 1 print paraview binary format
P 18 1 algorithm type for level set paraview print out standart
P 28 1 print fb to vtu file
P 30 0.2 print paraview results every ith second
P 40 1 print state file
P 42 0.2 print state file every ith second
P 180 1 print free surface vtp file
P 182 0.2 print out fsf every i th second

T 10 2 turbulence model kw
T 36 2 fsf boundary condition for turbulent dissipation

W 1 1000
W 10 246.816 inflow velocity
W 22 -9.81

X 10 1
X 11 0 0 1 0 1 0
X 13 2
X 22 319.289 floating body mass
X 23 9.7120 20.0 2.4308 floating body center of gravity
X 24 35 385 385 floating body momnet of inertia
X 180 1
Don't forget to arrange the free surface (F 60) and mass properties of floating body (X 22, X23, X 24).

You can also change mesh and domain size.

I hope that helps. Best regards.
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Old   June 9, 2021, 10:15
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Arun Kamath
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In addition remember to activate/ deactivate the degrees of freedom that you want/ don't want in X 11
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Old   June 9, 2021, 12:28
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Will
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Thank you for the guidance thus far. I will explore what I am able to with the input.

For clarity's sake in future replies, I have been able to run what appears to be a successful simulation with a rectangular floating body in the numerical wave tank, however, when switching to a cylindrical floating body the simulation fails. The only presumptive reason I have been able to identify, to this point, is a failure of the program to calculate the volume of the cylinder correctly, as it is often negative and on the order of 10^10+, when the prescribed dimension of the cylinder are obviously much smaller and much more realistic (i.e. r = 8.9 cm, L = 69 cm).

If the error's persist, I will post my input files for review by someone more familiar with the software, but again, thank you for the information provided so far!
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Old   June 9, 2021, 14:31
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Quote:
Originally Posted by ali_b124 View Post
Hello Will,

I am also trying to analyze floating body using reef3d.
The following options worked for me. For control.txt file:



For ctrl.txt file:



Don't forget to arrange the free surface (F 60) and mass properties of floating body (X 22, X23, X 24).

You can also change mesh and domain size.

I hope that helps. Best regards.
I am able to run your simulation when the floating body is removed. However, since I did not have your input .stl file, I replaced the floating body with a simple rectangular box, adjust the descriptive inputs (i.e. mass, center of gravity, moment of inertia) accordingly. When the rectangle box is there, the simulation fails with the similar "critical velocity exceeded" type warning. The input files that I use for the rectangular box are attached, could you perhaps see where I made an error with the input? (Note: ctrl - Copy.txt is named as such so that I could keep a record of the failed input while proceeding with my own exploration.)

Regards and appreciations!
Attached Files
File Type: txt ctrl - Copy.txt (981 Bytes, 9 views)
File Type: txt control.txt (200 Bytes, 7 views)
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Old   June 10, 2021, 04:13
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Arun Kamath
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Hi Will,
Your input seems to be fine with respect to the floating body. I see that you run this for current and not waves. With that, I would say look at the following aspects:
W 10 is the discharge and not the velocity. Too high a value here can cause "exceeding critical velocity" problem.

I would also recommend using B 76/ patch boundary conditions to better define and control and inflow and outflow.

Lastly, while CFL =0.3 works just fine, if the velocity errors persist, you might want to reduce the value.

Addressing another query in the thread above:
The floating objects currently do not have a collision detection algorithm. Therefore, if the object is too heavy and sinks (or sinks for other reasons) it will sink out of the domain as it does not detect the floor of the tank either. Of course by this stage the simulation is deemed to have crashed.

That said, I am not sure why your cylinder sinks
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Old   June 10, 2021, 16:01
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Hello Kamath,

Yes, the input files for the simulation above are for current, as I am attempting to run Ali's simulation to better understand. Now that I have started to better understand the parameters pertaining to the floating body, I'll soon be transition to my own simulations, which I hopefully will be able to perform now thank to all of your guidance.

If problems continue to present themselves, I will submit a new set of input files that will reflect my own wave simulations along with my questions.

Thank you all so far!
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