A Calculation Method of Hydrodynamic Forces and Moment on Vertical Body of Revolution (2nd Report) : 2nd-Order Seady Forces and Moment, and Long Period Motions of Heave and Pitch

Abstract

In our previous paper, we carried out calculations of linear hydrodynamic forces and moment on vertical body of revolution considering its property of axisymmetry. Then we confirmed the accuracy of this calculation method from the comparison of the results of the calculation with those of the experiment. In this paper, first, we made the calculation of 2nd-order steady forces and moment on the basis of the method presented in the previous paper and compared the results with model tests in regular waves. The calculation method adopted in this study is based on the regular perturbation method, and steady forces and moment are calculated by the integration of hydrodynamic pressure over the wetted surface of body. The calculation results showed good agreement with the experimental results. Secondly, we carried out the motion tests in irregular waves using a bottle type model with long natural periods of heave and pitch. Long period motions of heave and pitch were observed in the model tests as we have expected. We calculated spectra of the slowly varying forces by Pinkster's method, estimated long period motions of heave and pitch and compared the calculation results with those of the model test. By the comparison, good agreement was obtained.