We present a computational method to assess whipping and springing effects on accelerations and sectional loads of ship structures, and to compare numerical results with model tests. The nonlinear rigid-body equations of motion and the linear equation of motion of the nodal degrees of freedom (vibratory modes) are implicitly coupled in the time domain with a Reynolds-averaged Navier-Stokes equations (RANSE) solver. Three finite element (FE) structure dynamics methods are described. Comparative measurements of motions, accelerations and sectional loads were obtained on the segmented model of a postpanamax containership.
It has increasingly become common sense that structural elasticity of ships is an important contribution to the life-cycle load spectra of wave-induced hull girder stresses. Long-term full-scale measurement campaigns (e.g. Kahl and Menzel, 2008; Storhaug et al., 2003; Storhaug, 2007; Vidic-Perunovic, 2005) underline this point of view, although they do not indicate a general level of load amplification. This is most likely due to varying magnitudes of vibration excitation for different ship types and sizes, areas of operation, loading conditions, ship speeds, etc.; see Storhaug (2007) for an assessment of the impacts of different operational conditions. Nevertheless, classification society rules still operate with constant overall safety factors to account for the dynamic amplification of structural stresses. Therefore, an effort has to be made to establish improved prediction tools that include effects of ship structural elasticity in the design and assessment process of ship structures. Not only is the amplification of sagging and hogging extreme values due to severe slamming impacts and consecutive vibration of concern, but the increase in load cycles at a broad range of load levels affects the whole stress spectrum and thus contributes to fatigue damage. Here we restrict ourselves to demonstrating the capabilities of the developed method.
