Simulation based calculation of ship motions in extreme seas with a body-exact strip theory approach

For all design phases of naval vessels, the fidelity of seakeeping calculations in extreme seas is open to discussion due to the inadequacy of the linear theory of ship motions. Currently the computer-generated time series of ship responses and wave height (the real time computer experiments) are utilized to calculate the distribution of the vertical distortion, shear force and bending moment by means of “ship hydroelasticity theory”. Inspired by these studies a simulation based calculation of symmetric ship motions is performed in long crested irregular head seas, in addition with a body-exact strip theory approach. The scope of this study is limited to the ship motions only. Verification is achieved utilizing the spectral analysis procedure which contains the discrete Fourier transform (DFT) and the smoothing algorithms. The results are compared with the experimental data, and the ANSYS AQWA software results. The simulation results provide adequate data for the extreme responses. This state-of-the-art method in addition with a “body-exact strip theory approach” ensures the consistent assessment of the seakeeping performance in extreme sea condition. As a result, it is evaluated that this calculation method can be used in the design stages of naval platforms.

Study on Ship Structural Hydroelasticity and Fatigue Assessment in Irregular Seaways

This paper introduces an analysis of ship hydroelasticity for a fatigue assessment of ship structural design. In this study, the hydroelastic analysis for springing and whipping is carried out by using a fully coupled three-dimensional BEM-FEM approach with two-dimensional slamming theoreis, and a sequential fatigue assessment is performed. The fatigue damage is decomposed to wave frequency and high frequency components. Furthermore, the high frequency component is again decomposed to 1st harmonic springing, super harmonic springing and whipping contributions. This decomposition is achieved using a modal superposition principle. Amount of the contributions are compared in irregular sea states.

Reflections on the structural dynamics of floating beams and ship hulls in waves

The paper aims to shed light on links between the classical modal superposition analysis of ship hydroelasticity and the alternative formulation, more recently developed, in which equations for structural deflection and hydrodynamic pressure are coupled explicitly. The analysis is focused on a simple two-dimensional model of a uniform beam in small-amplitude waves. A new numerical representation is presented (based on a series of Legendre functions). Matrix equations are developed which provide links between the two formulations, and illustrative results are discussed. The influence of the beam flexibility on deflections and bending moments is shown, and the contributions of added mass and added damping effects are considered. The elastic wavelength in the floating beam is shown to be an important parameter.