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Old   January 21, 2022, 13:20
Default Alletto - 2022 - Comparison of overset mesh with morphing mesh
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Håkan Nilsson
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Comments and questions are welcomed on the article Alletto, Comparison of overset mesh with morphing mesh: Flow over a forced oscillating and freely oscillating 2D cylinder, OpenFOAM Journal, January 2022, https://doi.org/10.51560/ofj.v2.47.
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Last edited by bigphil; April 11, 2022 at 08:02. Reason: Update date format
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Old   January 21, 2022, 13:31
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Michael Alletto
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Thanks Håkan for opening the thread. I'll try to answer any questions which arise on the paper to my best.

Michael
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Old   February 4, 2022, 02:15
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Quote:
Originally Posted by mAlletto View Post
Thanks Håkan for opening the thread. I'll try to answer any questions which arise on the paper to my best.

Michael

How to calculate the work done as you have shown in the paper?
How to run the case of morphing mesh by considering both fluid and structural forces?

I tried to run your case (https://wiki.openfoam.com/1Dof_sprin...ichael_Alletto)

I will really appreciate if you can help me.
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Old   February 4, 2022, 07:52
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Regarding the work done there is the formula in the paper and the python script in the case file
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Old   February 5, 2022, 22:44
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I am learning Vortex Induced Vibrations and want to seek guidance from you.

I run the tutorial for Morphing mesh case to validate the results of Mittal (2 DoF). I calculated the values for the case of U*=4 , m*=10,Re=100
The values for the simulation parameters come out to be:

nu= 1.0496E-06
K=148.28
RhoInf=148171.24

The results of the X and Z centre of mass comes to be way lower than the published in your paper. Please guide me. In the below text, I have mentioned my dynamicMeshDict file.

sixDoFRigidBodyMotionCoeffs
{

accelerationRelaxation 1.0; // 1
accelerationDamping 1.0; //1.0

patches (cylinder);
innerDistance 0.0008; //1.0 // equal to cylinder Radius
outerDistance 0.032; // 0.032 // near the main domain boundary

mass 0.03575;
centreOfMass (0.0 0.0 0.0); // initially the cylinder is at the origin
momentOfInertia (4.3472E-07 1.144E-08 4.3472E-07);

g (0 -9.81 0);
rho rhoInf;
rhoInf 14817.12; //1.0e-15 // this value should be as per the nu and rho value in transport properties
report on;

solver
{
type Newmark;
}

constraints
{


zxLine
{
sixDoFRigidBodyMotionConstraint line; // cylinder can displace only along the z-axis and c axis
centreOfRotation (0.0016 0.0 0.0016); // i think initially at z=d location 0.0016
direction (1 0 1);
}

yAxis
{
sixDoFRigidBodyMotionConstraint orientation; // blocked the rotation around the y-axes
centreOfRotation (0 1 0);
}
}


restraints
{
verticalHorizontalSpring
{
sixDoFRigidBodyMotionRestraint linearSpring;

anchor (0.0 0.0 0.00);
refAttachmentPt (0.0016 0.0 0.0016); // It is attached to the boundary of cylinder (radius)

stiffness 148.281; // as the case of U* 4
damping 0.00;
restLength 0;
}
}
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Old   February 6, 2022, 02:09
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For U* = 4 the oscillations are in general quite low. The cylinder starts to oscillate for U* = 4.7. But in general questions like wy are my results not good are difficult to answer. Better if you ask more specific questions
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Old   February 6, 2022, 10:10
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Quote:
Originally Posted by mAlletto View Post
For U* = 4 the oscillations are in general quite low. The cylinder starts to oscillate for U* = 4.7. But in general questions like wy are my results not good are difficult to answer. Better if you ask more specific questions
I have following questions:

Should the value of inner distance be equal to diameter or radius?
What’s the recommended value of outerDistance? The boundary of whole domain or somewhat in between the cylinder and main boundary ?
Should the constraint of line be applied for 2-DoF? When I removed the line constraint condition, the simulation diverges… do I need to refine the mesh ?
Should the value of refAttachmentPt be equal to cylinder diameter or zero?

Will really appreciate your guidance...
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Old   February 6, 2022, 15:09
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It is really difficult for my to understand what you mean. Can you post a question by the time and be more precise. Do you have specific questions to the paper. The topic of the thread is the paper and if you want some help for your work you should open a new thread I think
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Old   February 6, 2022, 15:21
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Quote:
Originally Posted by mAlletto View Post
It is really difficult for my to understand what you mean. Can you post a question by the time and be more precise. Do you have specific questions to the paper. The topic of the thread is the paper and if you want some help for your work you should open a new thread I think
Hi,

I intend to seek guidance from you. In the paper you have specified linear spring restraint used for the morphing mesh case. As per the OpenFOAM code, linear sping is first order motion equation but the VIV problem is second order motion equation. How come you can get similar results? Please correct me if I am wrong.
See below the code for the linear spring.
https://www.openfoam.com/documentati...8C_source.html
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Old   February 6, 2022, 15:32
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What do you mean by first or second order motion. I've never heard this terms. What kind of morphing case are you referring. I analyzed three cases. A case without fluid forces, a forced oscillation and a Viv.

If someone needs 15 minutes just to understand your question you will likely not get any answer.
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Old   February 6, 2022, 15:43
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Quote:
Originally Posted by mAlletto View Post
What do you mean by first or second order motion. I've never heard this terms. What kind of morphing case are you referring. I analyzed three cases. A case without fluid forces, a forced oscillation and a Viv.

If someone needs 15 minutes just to understand your question you will likely not get any answer.
Hi,
Linear Spring has equation F=Kx +c
While for VIV, the motion equation is Mx¨ + Cx˙ + Kx = Fx

Can you clarify how come linear spring constraint can solve the VIV equation?
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Old   February 6, 2022, 15:53
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The solid body motion solver solves the rigid body motion equation. The spring force and the fluid forces act on the body leading to the motion of the cylinder. This is written in the paper as well. Please read the paper carefully.
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Old   February 9, 2022, 06:16
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Quote:
Originally Posted by mAlletto View Post
The solid body motion solver solves the rigid body motion equation. The spring force and the fluid forces act on the body leading to the motion of the cylinder. This is written in the paper as well. Please read the paper carefully.
Thanks for clarifying. I was confused with the file you shared on your Github and the openfoam journal. Nice work and well documented.
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Old   February 14, 2022, 15:33
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Marcelo Italo Adotti
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Hi Michael,


Nice job!


I am currently working with OF overset and some validation tests. I have a doubt about the "inline oscillating cylinder" condition, the motion applied in your paper is on the x-axis, co linear to the incident flow. Any reason why it is not with respect to the "z" axis?.


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Old   February 15, 2022, 00:57
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Hello Marcelo,

No no specific reasons. You can also enforce the motion in z-direction or do a combination of the two
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Old   February 15, 2022, 01:15
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Hi Alletto,

can you recommend me reading material that explains how the 6 DOF motion is solved using dynamic mesh. I wish to learn the mathematical aspect.
Many thanks in advance.

Regards.
Ansab


Quote:
Originally Posted by mAlletto View Post
Hello Marcelo,

No no specific reasons. You can also enforce the motion in z-direction or do a combination of the two
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Old   February 15, 2022, 04:52
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Regarding the translation motion, the equation are in the paper. Regarding the rotation, I started but never ended a tutorial where I summerized the equation solved. Find the pdf attached.
Attached Files
File Type: pdf torqueFreeMotionAxisymmBody.pdf (157.7 KB, 24 views)
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Old   February 16, 2022, 14:34
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Is someone is interested the case files of the paper can be found here https://gitlab.com/mAlletto/openfoam...ases4PaperSend
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Old   February 18, 2022, 15:21
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Can you please explain how can I calculate spring constant(k) for a square cylinder having Re=100 , U*=6 with the equations ? Kind regards.
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Old   February 18, 2022, 16:10
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U* = Uoo/(fn D) , fn = ω/(2 π) = (k / m)0.5/(2 π)

So if you want to achieve a given U* for a given diameter of the cylinder with a given mass and inflow velocity you have to set k accordingly.

Hope this helps
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