Study on nonlinear responses of a high-speed ship running in waves based on the Volterra model
Date Issued
2007
Date
2007
Author(s)
Tiao, Wen-Chuan
Abstract
It is well known that the hydrodynamic responses of a high-speed vessel traveling in regular head waves even of moderate wave height can show significant nonlinear behavior, and so linear statistical techniques become insufficient for predicting the statistics of responses in irregular waves. On the other hand, it has been shown that an approximate third-order Volterra model is applicable to handling the statistics of some nonlinear seakeeping problems, such as motions and vertical hull girder loads. In the present study, the focus is on the nonlinear behavior of the pressure acting on the hull surface of a high-speed vessel in waves, especially on the pressure responses of alternately wet and dry areas near waterline and on the bow zone with high deadrise angles that may be subject to slight impact and water pile-up effects. To clarify the validity of applying Volterra modeling to this problem, a series of experiments in regular and irregular head waves are carried out, and approximate third-order and fifth-order Volterra models with proposed algorithm for finding frequency response functions (FRFs) were applied as a means of validation. It was confirmed that the approximate third-order Volterra model has adequate accuracy to simulate deterministically the variation of pressure responses in regular waves of different wave steepness up to a wave amplitude to wavelength ratio of 0.01 even for the highly nonlinear pressures acting on the above-mentioned areas of the hull surface. In additions, further validation was performed using experimental data and theoretical calculation in irregular waves. The frequency response functions (FRFs) obtained both from the experimental data or theoretical calculation in regular waves were applied to the approximate third-order Volterra model combining with the input of irregular waves to simulate deterministically the responses in irregular waves of sea state five, and then the spectra and statistics were analyzed. Through the comparisons of the simulated time histories, variance spectra, and statistics such as cumulative distributions of peak values, probability density functions with the experimental results of motions, accelerations and pressure responses in irregular waves, it was confirmed that the approximate third-order Volterra model has adequate accuracy to simulate deterministically and statistically the pressure responses in irregular head waves up to a sea state of five even for highly nonlinear and non-Gaussian pressures acting on the above-mentioned areas of the hull surface.
Subjects
Nonlinear pressure
High-speed vessel
Third-order Volterra model
Frequency response function
Type
thesis
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