Methodology for wave force monitoring of bottom-mounted cylinder using the measurement of the wave surface elevation around the body surface

Abstract

This paper presents a methodology to estimate the wave force on a bottom-mounted cylinder using the measured signals of wave surface elevation around the body surface of the cylinder. Based on the potential theory, the formulae are derived in a general manner for bottom-mounted cylinders of arbitrary cross section. Considering the difficulty of decomposing the signal of wave surface elevation measured by wave gauges, a linear estimation method is developed to achieve an approximate estimation of the wave loads on cylinders. A hydrodynamic experiment was conducted on a circular cylinder in a random wave field to validate the effectiveness of the proposed method. The horizontal wave forces and bending moments directly measured by force balance are employed for the validation of the proposed estimated results using the measurement of the wave surface elevation by wave gauges. Error analysis is also conducted in the frequency domain to investigate the effects of the linear approximation. The analysis results indicate that the proposed method can effectively estimate the wave loads acting on the cylinder. The linear approximation method slightly underestimates the wave loads of the difference-frequency component, while overestimating that in the sum-frequency region.