Wavelet based detection of vortex shedding around a cylinder oscillating in still water

Document Type : Original Article

Authors

1 Assistant Professor, Road, Housing & Urban Development Research Center;

2 Associate professor, School of Civil Engineering, University of Tehran

3 Assistant Professor, School of Civil Engineering, University of Tehran, Tehran, Iran

Abstract

The present paper aims to study the lift forces acting on a cylinder oscillating in still water from spectral point of view. In the previous researches, vortex shedding frequency has been related to the fundamental lift frequency. Here, the wavelet analysis is used as a relatively new concept in spectral analyses. The simultaneous time-frequency representations of the lift forces are investigated to localize the flow induced transitory characteristics. The peaks in the wavelet coefficients attributed to vortex shedding are studied. The abrupt changes in the lift forces have also been studied by discrete wavelet decomposition. Small spikes have been observed in the results due to vortex shedding. Wavelet analysis is considered as an efficient alternative method to predict vortex shedding for larger Keulegan-Carpenter numbers (KC). Two different gap-to-diameter ratios, 0.1 and 1.0, are considered to account for the effect of bed proximity. Regular vortex shedding is suppressed for lower gap ratios; this fact is confirmed by wavelet analysis as well. The KC numbers in the present study are in the range of 15 to 40. The flow is in the subcritical regime with Reynolds number in the range of 9500-26000. The cylinder and the plane bed are both smooth.

Keywords

References

[1]Hudgins, L., Kaspersen, J.H., (2004). Wavelets and detection of coherent structures in fluid turbulence, Wavelets in Physics, Edited by J.C. Van Den Berg, Cambridge University Press, UK, 201-226.
[2] Williamson, C. H. K., (1985). Sinusoidal Flow Relative to Circular Cylinders. J. Fluid Mech., 155, 141-174.
[3]Maull, D. J., Milliner, M. G., (1978). Sinusoidal Flow Past a Circular Cylinder, Coast. Eng., 2, 149- 168.
 [4]4.Sumer, B.M. and Fredsoe, J., (2006). Hydrodynamics around Cylindrical Structures, Advanced Series on Ocean Engineering - Volume 26, World Scientific Publishing Co., Singapore.
[5]Kenny, J. P. and partners Ltd., (1993). Evaluation of Vortex Shedding Frequency and Dynamic Span Response, Development of Guidelines for Assessment of Submarine Pipeline Spans, Background Document One, OTI93614, Published by Health and Safety Executive.
[6]Grass, A. J., Kemp, P.H., Stuart, R. J., (1981). Vortex Induced Velocity Magnification and Loading Effects for Cylinders in Oscillatory Flow. SERC London Centre for Marine Technology. Report Number FL 28 January.
[7]Isaacson, M., Maull, D. J., (1976). Transverse forces in vertical cylinders in waves, J. Waterw. Port Coast. Ocean Eng., Div. ASCE WWI.
[8]Naeeni, S.T.O., Sadaghi, S.M., Narayanan, R., (2013). Effect of bed proximity on the in-line forces acting on a cylinder oscillating in still water, Ocean Eng.
[9]Naeeni, S.T.O., Sadaghi, S.M., Narayanan, R., (2015). Spectral Features of the Pressure Distribution Around a Cylinder Oscillating in Still Water, Coastal Engineering Journal, Vol. 57, No. 3.
[10] Addison, P. S., (2002), The Illustrated Wavelet Transform Handbook, Introductory Theory and Applications in Science, Engineering, Medicine and Finance. Institute of Physics Publishing, Bristol and Philadelphia.
[11] Mallat, S., (2009). A Wavelet Tour of Signal Processing, Elsevier Inc., United States.
[12] Jerri, A.J., (2011). Introduction to Wavelets, Sampling Publishing, Potsdam, New York.
[13] Naeeni, S.T.O., (2003). Force on Yawed Circular Cylinder Oscillating over a Plane Bed in Current, PhD thesis, UMIST, Manchester, UK.
International Journal of Coastal and Offshore Engineering
Volume 6, Issue 4
November 2021
Pages 44-59

Files

Share

How to cite

Statistics