For non-wall-sided ship hulls experiencing severe vertical relative motion in large amplitude regular waves with high forward speed, there are many components with different frequencies in the bending moments. In addition to the usually considered wave encounter component and hull girder vibration components, many higher-order harmonic components exist in the bending moments, which have non-negligible contributions to the nonlinearity of bending moments. The higher-order harmonic components are introduced by nonlinear hydrodynamic forces and influenced by the elastic vibration component. When the ship sails in regular waves with the first elastic frequency close to an integral times of wave encounter frequency, springing occurs and the combined bending moment will reach its extreme values. For vertical motions, e.g. heave and pitch, there are almost no higher-order harmonic component in the responses. Hence, these motions can be considered as monochromatic responses in regular waves. In model tests or theoretical analysis of unconventional ships in which springing or whipping can occur, the wave parameters and the ship speed must be carefully selected to achieve representative results. The design values of bending moments in some rules and regulations are based on formulae for wave-induced bending moments that do not reflect the particular features of springing or whipping responses. It is necessary to consider design values for flexible ships by applying direct calculation methods.
Experimental and theoretical investigation of higher-order harmonic components of nonlinear bending moments of ships
Experimentelle und theoretische Untersuchung von harmonischen Komponenten höherer Ordnung von nichtlinearen Biegemomenten von Schiffen
Ship Technology Research / Schiffstechnik ; 47 , 4 ; 143-154
2000
12 Seiten, 12 Bilder, 3 Tabellen, 17 Quellen
Article (Journal)
English
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