Experimental Assessment of Vertical Shear Force and Bending Moment in Severe Sea Conditions

Abstract

Recent studies have benchmarked the prediction of wave vertical bending moment (VBM) of ship in waves [1][2], and found significant scatter among the numerical codes. Unfortunately, experimental data in extreme waves, that are relevant to ship design, are not often easily accessible, nor completely fitted to rigorous comparison to numerical codes. Then, the improvement of numerical tools and the modelling of ship’s internal loads still requires accurate experimental data measured in steep waves (ratio wave height H to wavelength λ, H/λ = 0.1) where the ship behavior and loads are modified by non-linearities. Thus, in order to validate simulation codes, which underlies rules requirement, and to establish criteria that makes ships safer to sail in severe sea conditions, experiments are carried out in the 50m × 30m × 5m hydrodynamic and ocean engineering tank of Ecole Centrale Nantes. A 1/65th scaled model of a 6750-TEU containership is used. The ship is moored and several combinations of wavelength and wave height are tested. While segmented hulls are commonly instrumented with strain gauges, the present experiments are performed on a segmented hull with a 6DOF sensor located close to the amidship. This setting allows for a very stiff model which dramatically reduces the hydroelastic effects. According to previous study [1], the position of the sensor is chosen where the bending moment is supposed to reach a maximum value. The model motion is measured through a Qualisys IR tracking system and accelerometers are located on the fore and aft of the beam. Also, each of the 9 segments is equipped with a 3DOF dynamometer to measure the hydrodynamic loads on the hull. This allows for recovering the hydrodynamic loads on the segments and then to compute the shear force and bending moment discretized all over the ship length. A comparison is therefore possible with the 6DOF sensor. Details of the computations are given in the paper. A particular attention is paid to the reproducibility and repeatability of the tests. The innovative experimental setup and the measured data are presented in the paper. Based on previous studies [3], the effects of the non-linearities are also discussed.