Physical model studies and system identification of hydrodynamics around a vertical square-section cylinder in irregular sea waves

In the present study, the results obtained from a series of experiments conducted in a wave flume were investigated to assess the hydrodynamic characteristics and pressure distribution around a vertical square-section cylinder in irregular waves. Experimental measurements were taken at moderately high Reynolds numbers and low Keulegan-Carpenter numbers with the cylinder at different rotation angles. The ARMAX (Auto Regressive Moving Average with exogenous input) parametric model was proposed as a numerical approach to model the variation of the hydrodynamic pressure on the cylinder over time based on the concept of system identification. The validation results demonstrated that the ARMAX model was able to simulate the signals of the wave pressure on the front side of the cylinder but failed for most of the points located after the separation points. The results obtained using the principal component approach and the concept of subspace angle implied that the efficiency of the proposed model depended on the onset of nonlinear behavior in the measured data. It was due to the non-linearity induced by the flow patterns after the separation points.

► We examine the pressure distribution pattern around vertical square-section cylinder. ► We study the relation between the incident wave and the pressure for the sharp-edged body. ► The ARMAX model is able to simulate the time variation of pressure on the front side. ► The identification failed in the other cases for the all the sides of the cylinder. ► We use the concept of the principal component and subspace angle to inspect the problem.