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-   -   Vortex induced Vibrations (http://www.cfd-online.com/Forums/openfoam/96697-vortex-induced-vibrations.html)

aravindh28.4 January 30, 2012 02:58

Vortex induced Vibrations
 
I am currently doing a simulation of "Vortex Induced Vibrations" for my bachelor thesis on OpenFOAM(version2.1.0), and want some help in understanding some of the term in the pointDisplacement file in the 0 folder of the case file(../openfoam201/tutorials/incompressible/pimpleDyMFoam/wingMotion/wingMotion2D_pimpleDyMFoam/0).

What exactly is the orientation tensor and the angularMomentum entry in the pointDisplacement file?

Also I am will be changing the dimension of the body(cylinder in my case) and hence have to change the anchor point of the spring. does this have to be done by trial and error or is there some way of finding the point co-ordinates in paraview?

I am new to this software, so please excuse me if these questions were basic.

MrAnderson February 3, 2012 19:19

Dear Aravindh,

I am doing PhD and also started recently with OpenFOAM simulations based on Vortex Induced Vibrations around a circular cylinder. For this, I have tried to modify the pointdisplacement file with respect to the cylinder. However, I also do not know how to implement diferent fields in this file. Like, 'orientation' to be just an example...

Maybe, we can try to help each other out since we want to simulate the same case?? Later on, I also want to extend the number of rigidbodies to consist of 4 cylinders and would like to know how to implement this?


All the best

/MrAnderson

aravindh28.4 February 4, 2012 04:59

Dear Mr. Anderson
Sure sir, by helping each other, both of us can progress. How far have you proceeded? My simulation is just a 2D case. So, orientation is not an issue for me. I just removed that matrix part from the file. It works... Now I need to know what exactly the spring attachment parameters mean physically, like the anchor, refAttachmentPt etc.

Kindly help me out in this regard.

MrAnderson February 13, 2012 18:22

Dear Arawindh,

Sorry for my late reply. I am still struggling with the same problem as you are. Parameters such as restLength, anchor, refAttachmentPt is also unknown for me. I'll try to work with this during the coming days. I will let you know if I achieve any progress.


Well, I've found out though that fixedAxis is for rotation and fixedLine is for pure translation. So, if only translation is desired, then it is just to remove fixedAxis and the corresponding angularmomentum.

Let's work on it and hopefully it will be solved!

niaz February 14, 2012 11:48

Dear Mr Anderson
Restlength = x0
refAttachmentPt= place that the force of string should apply
anchor = the distance from the spring hook to the object

mali May 31, 2013 00:25

Hi All,

I'm currently also simulating VIV problem. My case is a rigid circular cylinder supported by a one degree elastic system in the cross-stream direction. The solver that I uses is similar to the case in the tutorial wingMotion, as suggested by aravindh28.8 in the earlier post. I able to simulate the dynamic response at low reduced velocity, u* =<1 but at higher u* the simulation blows up. The mesh has changed very badly at this time, due to high displacement response.

I wondering if any OpenFoam user has ever successfully simulated the VIV problems for high reduced velocity value. Please advice me if you are.

Thank You,

-mali-

araujo February 19, 2014 16:25

which delta_x and delta_t are you using? stiffness and damping?

Maimouna April 10, 2014 05:53

Dear araujo,

I just started with OpenFOAM simulations based on Vortex Induced Vibrations (VIV) around a circular cylinder. For this, I have tried to modify the incompressible/pimpleDyMFoam/wingMotion/0/pointdisplacement file with respect to the cylinder, but unfortunatelly I don't get the result that you showed in http://www.youtube.com/watch?v=RPTcF_ClJ-E. So I need your help please to understand meaning with different fields in the poindisplacement file.

Many thanks in advanced.

Maimouna

Amit-1911 April 16, 2014 06:26

hiii all,

I am also trying to simulate the same case, but i am using uncoupledSixDofRigidBodyDisplacement as a displacement type, i am unknown about anchor, refattachmentpt and rest length under linear spring option, like what should be my anchor pt and all...
can anybody help me on this??

thanks in advance!!
Amit Dhage

Maimouna April 21, 2014 10:11

Dear Amit,

anchor = the distance from the spring hook to the object.
refAttachementPt = place that the force of string should apply.

Regards

Maimouna

Amit-1911 April 21, 2014 10:33

Dear Maimouna,

Thanks for reply!
I am not able to understand about 'Ref attachmentpt =place that the force of string should apply' what is this force of string??
Can you clarify a bit on this?

Regards,
Amit Dhage

Maimouna April 21, 2014 10:47

Dear Amit,

sorry, I didn't have more idea about it. I'm still stucking on that. If I get something to make more clarified, I will let you know than.

Regards

Amit-1911 April 21, 2014 13:03

no problem Maimouna, even i will let you know if get to know something...

Thanks & Regards,
Amit

araujo July 24, 2014 17:51

Quote:

Originally Posted by Amit-1911 (Post 487318)
Dear Maimouna,

Thanks for reply!
I am not able to understand about 'Ref attachmentpt =place that the force of string should apply' what is this force of string??
Can you clarify a bit on this?

Regards,
Amit Dhage

the place that the force of the string should apply is represented on this picture:

http://fluidsengineering.asmedigital...4501_1_f1.jpeg

when your body moves, it causes a displacement on the string, which causes a reaction on the string (F=k.x, x being the displacement and k the stiffness of the spring.

Maimouna July 25, 2014 19:25

Dear Leonardo,

I'm nearly finished my case, but I'm still looking how to make cylinder moves up and down in y-axis? In my case, It works fine in x-axis but when changed it to y-axis, it gives me error, why? Any idea please??

Many thanks in advanced.

Amit-1911 July 26, 2014 04:23

Dear Maimouna

Thanks for your reply!!

Can you share the point displacement file with me, if you don't mind because i am not able to simulate the case even in one DOF.
Your help in this matter will be great!

Thanks and regards,
Amit Dhage

araujo July 27, 2014 17:32

Quote:

Originally Posted by Maimouna (Post 503207)
Dear Leonardo,

I'm nearly finished my case, but I'm still looking how to make cylinder moves up and down in y-axis? In my case, It works fine in x-axis but when changed it to y-axis, it gives me error, why? Any idea please??

Many thanks in advanced.

Maimouna,

I believe it has something to do with your mesh and the solver you are using. Certain solvers cannot handle big displacements and tends to diverge. Check out your time step too. I strongly recommend the use of a second order aproach for the time integration.

araujo July 27, 2014 17:33

How is your domain? The x length relative to the cylinder and y length? And how many points in each axis are you using?

Amit-1911 July 27, 2014 23:54

Dear Maimouna,

The ref attachment point is the point on the cylinder as you said. I tried that but the cylinder moves down, i don't know why?, may be due to its own weight. The downward movement of the cylinder deforms the mesh badly and the solution diverges.
The spring is on the negative Y axis for your information.
Kindly help me on this.

Regards,
Amit Dhage

araujo July 28, 2014 03:42

Quote:

Originally Posted by Amit-1911 (Post 503367)
Dear Maimouna,

The ref attachment point is the point on the cylinder as you said. I tried that but the cylinder moves down, i don't know why?, may be due to its own weight. The downward movement of the cylinder deforms the mesh badly and the solution diverges.
The spring is on the negative Y axis for your information.
Kindly help me on this.

Regards,
Amit Dhage

Dear Amit,

I believe it has something to do with the "constraints" on your dynamicMesh dictionary. Check out if you set up the right axes and lines for your body to move.


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