Experimental investigations of vibrations of cylinder in water at a plane bottom due to random waves

In the wave flume of the Institute of Hydroengineering vibrations of an elastically supported cylinder placed in the vicinity of a plane rigid bottom due to random water waves were investigated. The random waves were generated by feeding a time series generated on a computer into the control system of the wavemaker. The elevation of free surface above the cylinder and accelerations of the end points of the cylinder have been measured. Analysis of the measured surface elevations shows that the description by generalised Stokes' wave theory to the random case is justified. The starting point for the description of motion of the cylinder was the theory of ideal fluids supplied with the potential theory solutions. The addition of experimental terms to the differential equations of motion is discussed. The analysis in the frequency domain leads to the spectral densities based on simplified relations but without any empirical coefficients. The analysis in the time domain leads to a numerical solution that describes well the characteristic features of real behaviour. The experiments prove that the theoretical solution based on the theory of perfect fluids reproduces qualitatively the basic features of phenomenon and is a good starting point for formulations that may be used are reliable in engineering practice.