We present a computational method that considers hydro-elastic effects to assess whipping and springing on accelerations and sectional loads of ship structures, and compare numerical results with model test and full-scale measurements. In the computations, rigid body motions are superimposed on elastic deformations, whereby the former can be of large amplitude while the latter have to be of small amplitude relative to rigid body motions. The nonlinear rigid-body equations of motion, the linear equation of motion of the nodal degrees of freedom (vibratory modes), and the Reynolds-averaged Navier- Stokes equations (RANSE) are coupled in an implicit way and solved in the time domain. Three implemented structure dynamics methods are described. These methods are based on Finite Element (FE) approaches. Comparative measurements of motions, accelerations, and sectional loads were obtained on a postpanmax containership. Representative computed time series of vertical bending moment amplitudes for the rigid hull and the elastic hull are shown.
It has more and more 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, see 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 exctitation 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. Not only the amplification of sagging and hogging extreme values due to severe slamming impacts and consecutive vibration is of concern, the increase in load cycles at a broad range of load levels affects the whole stress spectrum and thus contributes to fatigue damage.
