Wave force measurement on a large-scale vertical cylinder using a visual technique

Visual techniques were used to identify the wave force on a large-scale vertical cylinder for the first time in this study by tracking the dynamic waterlines around the cylinder. Experimental validation of the proposed method with two types of waves, regular and irregular, was conducted in a wave flume. Four cameras were used to capture images synchronously, and the dynamic waterlines around the cylinder were identified using a grayscale gradient of pixels. Based on the potential theory, the wave force, including the linear and part of the second- and higher-order force components, was identified using recursive least squares (RLS) in real-time. The identified wave force agreed well with the wave force measured by the load cells, particularly the linear wave forces. The identified results could be significantly improved by considering the nonlinear wave forces. The proposed method has broad applications for laboratory measurements of wave loads on cylindrical structures.