An Experimental Study on Hydrodynamic Forces Acting on lrregularly Oscillating Cylinders

Abstract

In order to evaluate Morison equation with constant coefficients, measurements of the hydrodynamic viscous forces acting on irregularly oscillating circular cylinders and flat plates, which are deeply submerged, are carried out. Constant drag and mass coefficients are obtained for each process by frequency domain analysis using spectra as well as time domain analysis. The obtained coefficients by the two methods are different from each other. Moreover, the frequency domain analysis is valid in a region of very limited Keulean-Carpenter number. And it is confirmed that the error of the predicted value by Morison equation with the obtained constant coefficients increases with Keulegan-Carpenter number, because of variety of vortex shedding of every swing. This suggests that hydrodynamic coefficients varying from swing to swing should be used for accurate prediction of viscous forces acting on an oscillating blunt cylinder.