# Oscillating cylinder

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 September 5, 2006, 01:28 Oscillating cylinder #1 MC Guest   Posts: n/a Hi, I am calculating the oscillating cylinder problem in 2D domain with STAR-CD. I compared the results from different methods, such as velocity inlet, momentum source and moving grids. But, It was found that the results are different except the time that the maximum X-direction force appears. Do I have to add some added mass component ? Please help me !

 September 5, 2006, 07:50 Re: Oscillating cylinder #2 Mani Guest   Posts: n/a Describe your problem in more detail. Does the cylinder perform forced oscillations or is it suspended on a spring and free to oscillate, or something else...? Describe the motion of the cylinder. (tranverse to the flow direction or in line, or both). "Results are different" <-- what does that mean? What is different from what? You numerical results differ from experimental data, or from other numerical data...? How are they different? What are the important parameters (e.g. Reynolds number, mass ratio, structural damping)? Have you tried the case of vortex shedding over the stationary cylinder at that same Reynolds number? You should. Let's start with that, and add anything else you can tell us about the case.

 September 5, 2006, 09:32 Re: Oscillating cylinder #3 MC Guest   Posts: n/a Thank you very much for your comment! Yes, I had to describe my problem more detail. The cylinder is under forced oscillations in line direction of flows. And I meant that the difference is magnitude of in-line force (such as drag component). The Reynolds number is above 10^6 and there is no structural damping. I tried to calculate the velocity profiles with different methods as I mentioned. The results are almost same. But the in-line forces are different. Actually considering a moving obstacle with constant speed, we treat the problem as a stationary body with moving flows. But, in case of oscillation body this is not a stationary problem. My question is how To compare the results between computation and experiment.

 September 5, 2006, 18:22 Re: Oscillating cylinder #4 MC Guest   Posts: n/a In my previous meassage, the velocity profiles with different methods were calculated without the cylinder. In that case, the results are almost same.

 September 6, 2006, 07:05 Re: Oscillating cylinder #5 Mani Guest   Posts: n/a Before you perform the computations with cylinder motion you should try the case with a stationary cylinder (at constant velocity). How well do you predict the drag in that case, as compared to experiments?

 September 6, 2006, 21:41 Re: Oscillating cylinder #6 CH Guest   Posts: n/a Hi, i'm also doing oscillating cylinder. however, mine is a tranverse case and i'm using immersed boundary. problem arises when the cylinder starts oscillating. the cl plot is not smooth and has lots of sudden up/down. i've verfied with stationary and also rotating cylinder and the result's are similar. is there an intermediate step which i can advance to before going to the oscillating problem? i'm trying to detect the error step by step...

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