VIV of cylinder using pimpleDyMFoam
Dear all, currently I'm modifying the wingMotion case in the tutorial to a 2D circular cylinder. The main work in the modification lies in the pointDisplacement file. The cylinder is supposed to vibrate only in the y-axis(due to lift force). So I used the following lines:
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constraints What does this message mean?? |
HI!
In my cylinder VIV simulations with just one degree of freedom, there were no problem. However, when I extended my case to 2DOF(in-line motion and transverse motion, both translational), namely, adding one more fixedLine constraints and one more linearspring to the one-degree-of-freedom case, the cylinder became static!!:confused::confused: Why is this happening? could someone please explain? Here is my pointDisplacement for the 2DOF case: Code:
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Greetings kkpal,
I've moved your second post from the other thread where you had posted on: http://www.cfd-online.com/Forums/ope...ic-mesh-4.html - I moved it so that the discussions wouldn't overlap and become too confusing on who was answering to whom. I had somewhat detailed look at your description and file. From what I can figure out, the problem is that it's only "static" because it appears to be static, but it does not mean that it won't move if more force is applied to it. My advice, is that you describe in detail the full case set-up and what exact commands you are using, because the problem seems to me to be something related to a very small detail that you're overlooking. Best regards, Bruno |
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Dear Bruno:
Thank you for your kind help. After several trials I changed the constraint from two fixedLines to fixedPlane and the problem was solved. One other thing, I found there are some differences between the implementation of the stiffness k in OpenFOAM and in some other papers. In related literature, the stiffness k is specified directly in x and y directions, with constant values. However, in OF, the stiffness is defined by the spring, which has an anchor point and an attachment point. In this way, a initially vertically placed spring could also account for the horizontal motion. The mechanism is shown below. The initial length of the spring is l0, the horizontal displacement of the cylinder is delta_x, so the elongation of the spring is calculated by delta_l=sqrt(l0^2+delta_x^2)-l0, thus the force in the spring is F=k*delta_l. The force could be decomposed into x and y direction. In this case, the effective stiffness of the spring is no longer a constant. If one aims to simulate 1 DOF problem of cylinder viv, it is no problem since one only needs to place the spring along the direction of motion. It is also OK to simulate 2 DOF problems whose x and y directional stiffness are the same, in this case one needs to place one spring in the center of the cylinder(anchor point and attachment point are both in the center of mass, thus the components of the spring force is equivalent to having two springs in both x and y directions).The problem arises when one want to simulate 2 DOF problems with different stiffness constants k in x and y directions. Because of the mentioned reason, the effective stiffness k in both x and y directions will not keep unchanged during the cylinder motion. Quote:
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Hi kkpal,
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OK, the detail I find cute about papers is that they have to summarize (and many times omit) a ton of principles that are important for the simulation to be accurately performed and/or reproduced. I say (write) this because the papers do not necessarily have the fully realistic implementation, they might only have a simplified implementation. Which reminds me, on the other thread, in post #75, you can now find 3 possible implementations of this experiment: http://www.cfd-online.com/Forums/ope...tml#post525732 Going back to your question/issue, I have to ask you: if we ignore completely OpenFOAM's implementation, and focus on the real laboratory experiment, then what is the exact set-up you envision? Namely, how should the stiffness be physically imposed? I ask this because I'm not fully familiar with these VIV experiments, but if you can explain how the case should physically be set-up, then I should be able to translate it to OpenFOAM's point of view. Best regards, Bruno |
VIV for two cylinders in tandem
Hi guys - currently i am doing the viv for two cylinders in tandem.
I did quite OK with one cylinder , using pimpleDyMFoam with dynamic meshing...but fot two cylinders in tandem orientation, what the main thing to be changed? Because the simulation does not work.. Regards - Thankssss:confused: |
Viv cylinder
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I have a project of vortex induce vibrations (cylinder). One of this is a cylinder with RAS turbulence for Re > 300 and another with Laminar turbulence for Reynolds 40<Re<300. But if you want simulate this case for other Reynolds Re< 40 you can use the RAS case but you have to chanthe de turbulence off.
I'm new in this forum. Student of aerospace engineering. :RE |
Viv
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I forgot this text file to run de VIV simulation. Sorry this text file is in Spanish.
Please read it before the simulation. :Rodar los ojos: |
Different stiffness for x and y directions
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I have tried to place two springs with the same stiffness in x and y directions separately, i.e (-0.5 0 0.5) and (0 0.5 0.5). However, the result is not correct. I am trying to use only one spring placed at the centre of the cylinder as you mentioned. If possible, would you please give some suggestions when placing two springs with different stiffness in x and y directions? Thanks very much. Kind regards, Ze |
VIV cylinder issue: Floating point exception
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I tried using your "cilindro1" case, but I met the floating point excepetion. I used OpenFOAM 8, and only changed the solver from pimpleDyMFoam to pimpleFoam since pimpleDyMFoam is not supported in this version. I am new in CFD, anc could you help figure out the reason. Thank you in advance. |
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