Prediction of nonlinear vertical bending moment using measured pressure distribution on ship hull

Abstract

Accurate prediction of wave loads on ships and floating structures is paramount in the structural design stage. Use of a segmented ship model is a common method to quantify the wave loads. Nevertheless, the value could be measured only at segmented sections. To obtain the wave loads at any longitudinal position and to account for nonlinear features in the wave loads more precisely, local quantities of the pressure on the whole ship-hull surface need to be measured along with ship motions in waves. In this paper, an unprecedented experiment using a bulk carrier model has been carried out to measure the spatial distribution of wave-induced unsteady pressure by means of a large number of Fiber Bragg Gratings (FBG) pressure sensors affixed on the whole ship-hull surface, and at the same time the wave-induced ship motions and ship-side wave profile have been measured. In order to see hydrodynamic characteristics in nonlinear and forward-speed effects on measured and analyzed results, some computations with the linear frequency-domain Rankine Panel Method (RPM) and the nonlinear Computational Fluid Dynamics (CFD) method solving the Reynolds-Averaged Navier-Stokes (RANS) equations are made. Favorable agreement is found for the pressure distribution and resulting vertical bending moment between the results of the experiment and corresponding numerical computations. Validation of the measured pressure distribution has also been made through a comparison of the wave-exciting force and moment between the two independent results obtained by integration of the measured pressure over the entire wetted surface of a ship and by direct measurement using a dynamometer. Very good agreement is confirmed in this case, too. As another validation for the wave loads, a comparative study is made with the benchmark test data of a 6750-TEU container ship used for the ITTC-ISSC joint workshop in 2014; which also demonstrates remarkable agreement. The present study may provide a new research technique, especially in the experiment, for predicting the wave-load distribution and for studying local hydrodynamic features in wave-related unsteady phenomena.