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-   -   Oscillating cylinder - unidentified data (http://www.cfd-online.com/Forums/fluent/108606-oscillating-cylinder-unidentified-data.html)

stefanos October 28, 2012 12:57

Oscillating cylinder - unidentified data
 
Dear community,

I'd be very thankful if somebody could give me an opinion on the following issue:

I'm simulating a "2D oscillating cylinder in still fluid" problem within ANSYS Fluent 13.0, aiming to collect Cd, Cl values into file and estimating the corresponding forces at every timestep. However, i get no numbers after the comma (Cd values are in the right column):

" "Drag Convergence"
"Flow Time" "Cd"
2.00000e-02 1.#INF0e+00
4.00000e-02 1.#INF0e+00
6.00000e-02 1.#INF0e+00
.......", and so on...
I didn't face this problem in the past. Four months before i solved the same domain for different parameters of motion. My only intervention within this time period was moving the initial project folder into a disc, while i needed space for other numerical simulations, and placing them back, a few days ago in order to solve the new case.

Regards

Stefanos

stefanos October 28, 2012 13:08

To highlight the issue, i would like to ask, does this "#.INF0e+00" indicate infinite digits and if so, is there a way to avoid it? Unfortunately, i couldn't find any reference or related guidelines in the Fluent's "help" and manuals.

Quote:

Originally Posted by stefanos (Post 388948)
Dear community,

I'd be very thankful if somebody could give me an opinion on the following issue:

I'm simulating a "2D oscillating cylinder in still fluid" problem within ANSYS Fluent 13.0, aiming to collect Cd, Cl values into file and estimating the corresponding forces at every timestep. However, i get no numbers after the comma (Cd values are in the right column):

" "Drag Convergence"
"Flow Time" "Cd"
2.00000e-02 1.#INF0e+00
4.00000e-02 1.#INF0e+00
6.00000e-02 1.#INF0e+00
.......", and so on...
I didn't face this problem in the past. Four months before i solved the same domain for different parameters of motion. My only intervention within this time period was moving the initial project folder into a disc, while i needed space for other numerical simulations, and placing them back, a few days ago in order to solve the new case.

Regards

Stefanos


nitman118 June 4, 2013 10:06

could u explain in brief how you simulated the oscillation of cylinder in still fuid?

stefanos June 4, 2013 11:59

Some brief highlights of the problem are the following:

The problem is transient and requires a "DEFINE_CG_MOTION" udf. You can refer to the post http://www.cfd-online.com/Forums/flu...r-2d-case.html, as well. The key parameter is time, so there is an option to define the horizontal velocity of the wall boundary as a sinusoidal function of time within the udf script. The .c file for the particular problem should be compiled -not interpreted- in fluent. Then, the "dynamic mesh" module should be set up so that the udf of motion is hooked up to the wall boundary and the motion is defined as a "rigid body" one. In addition (as long as the problem is turbulent and requires k-ε or k-omega, etc. averaging), it is better that the same rigid body motion is attached to a -surrounding the wall fluid- zone that includes the boundary layer. This way you can get a better approximation of the flow close to the wall. This zone can be meshed with quad-structured elements. The external-deforming fluid zone should rather be meshed with tri-elements while the smoothing-remeshing options of the dynamic mesh module should be used instead of layering, that works fine for quad elements. The PISO pressure-velocity coupling algorithm works better for transient flows. You can refer to several other posts within this forum, as well, while the current case is extensively analyzed. You can also send me your details (email) so that we can have a closer look to your problem. As for the boundary conditions, these depend on the structure of your flow. However, a velocity inlet isn't appropriate for the still-fluid assumption.

Greetings,

Stefanos

nitman118 June 4, 2013 13:12

my email id is : nitman118@gmail.com .... i can share my files with you so that u can have a better idea... thanx fr the post...


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