WEAKLY NONLINEAR DYNAMIC ANALYSIS OF FLOATING BODIES IN WAVES

Weakly nonlinear dynamic responses of rectangular floating bodies are studied in this work. This study is based on a modified linear wave theory that gives a reasonable Froude-Krylov pressure distribution near the free surface. The idea of strip theory is then adopted to evaluate the Froude-Krylov force and the added mass and damping forces of the three dimensional floating body. The effects of instantaneous wetted surface and large motion of each strip are also considered. In the study, it is not necessary to limit the motions of the floating body to small motions. The results show that the new analytical method is more reasonable than the linear one. In order to verify the nonlinear result, comparisons between the degenerated nonlinear results with the linear ones were performed. The significant results of this study are summarized as follows: 1. The weakly nonlinear response amplitudes are different from the linear results especially around the resonance frequencies. 2. The upward and downward response amplitudes are not equal in some cases, especially in the range of high frequencies i.e. the suction and tilting phenomena as described by other researchers also occur in the proposed model. 3. In some cases, sub-harmonic motions appear in the nonlinear responses. 4. In the cases with large wave heights, unstable phenomenon occurred which can not be simulated in the linear analysis. From this study, the author thinks that the more reasonable approach adopted in the study should be recommended in the study of responses on floating bodies. The proposed approach includes the following considerations: (a) the modified linear wave pressure is adopted (b) the integration for the Froude-Krylov force is carried out from the instantaneous wetted surface; (c) the varying added mass and damping forces with the instantaneous draft of every cross section (strip) is considered.

Author dc:creator

• WANG DANHONG