Linear and Nonlinear Hydroelastic Analysis of High-Speed Vessels

Abstract

A linear formulation of ship hydroelasticity is presented. Appropriate body boundary conditions of flexible modes are obtained and the hydroelastic version of high-speed strip theory is established. A nonlinear time-domain simulation method is also presented. The total response is decomposed into linear and nonlinear parts. The linear part is evaluated using appropriate linear potential-flow theory and the nonlinear part comes from the convolution of the impulse response functions of linear ship-fluid system and the nonlinear hydrodynamic forces. Four high-speed vessels with different ship lengths but with similar body plan and internal structural arrangement are used as examples. The calculations of midship bending moments are carried out at different forward speeds and head sea states. The results show that the hydroelastic effect in linear extreme responses is insignificant and that the hydrodynamic damping plays a leading role in the flexible modes when the dynamic amplification of ship hull becomes important. The results also indicate that strong nonlinearity is the most prominent feature of high-speed vessels even in the moderate sea state and must be taken into account. The nonlinear influences are more remarkable in ships at large Froude numbers than in those at small ones, and more important in sagging moment than in hogging moment.