Time domain simulation of hydroelastic response of ships in large amplitude waves


Park, Jae-Hong (2006) Time domain simulation of hydroelastic response of ships in large amplitude waves. University of Southampton, School of Engineering Sciences, Doctoral Thesis , 185pp.

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Description/Abstract

The influence of non-linearities on wave-induced motions and loads has been the
focus of many investigations in the past few years and continues to be an important
issue. A number of two- and three-dimensional methodologies have been developed,
by and large, partly accounting for various non-linearities. Non-linear radiation, and
to an extent diffraction, is the main problem and its solution via a three-dimensional
method using Eulerian-Lagrangian schemes is likely to be complex and time
consuming for practical applications. On the other hand two-dimensional methods, in
spite of issues associated with accounting for forward speed, offer more possibilities
of making practical advances in dealing with non-linearities.

A two-dimensional hydroelasticity analysis for symmetric (i.e. vertical motions,
distortions and loads) dynamic behaviour in waves, including the influence of nonlinearities,
is presented in this thesis using two methods. In the first method the total
response is decomposed into linear and non-linear parts. The linear part is evaluated
using the conventional two-dimensional linear hydroelasticity analysis. The nonlinear
hydrodynamic forces are due to changes in added mass and damping
coefficients, as well as restoring and incident wave forces, all evaluated over the
instantaneous wetted surface. Non-linear forces due to slamming (bottom impact and
flare) and green water (treated in a quasi-static manner) are also added. One aim of
the thesis is to investigate the influence/importance of each of the non-linear
hydrodynamic forces. Furthermore, the effects of assumptions made when using
these hydrodynamic forces, e.g. frequency dependence of added mass, neglecting the
damping coefficients in some components and evaluation of derivatives, are
investigated. The solution in the time domain is obtained using direct integration and
convolution integration, the latter based on the impulse response functions of the hull
in its mean wetted surface. In the second method the response, including nonlinearities,
is obtained from the solution of one system of equations of motion, where
the added mass and damping coefficients and the restoring, incident wave and
diffraction forces are evaluated at the instantaneous draft. Non-linear forces due to
slamming (bottom impact and flare) and green water (treated in a quasi-static
manner) are also added.

Both methods are applied to the S-175 containership, for which experimental
measurements of motions and loads in large amplitude regular head waves are
available. Comparisons made between predictions and measurements (heave and
pitch motions, vertical acceleration and vertical bending moment) indicate good
overall agreement. The comparisons also show that the influence of flare slamming is
important for the range of speeds and wave amplitudes investigated.

Item Type: Thesis (Doctoral)
Subjects: V Naval Science > V Naval Science (General)
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences
ePrint ID: 142721
Date Deposited: 19 Aug 2010 11:06
Last Modified: 27 Mar 2014 19:04
URI: http://eprints.soton.ac.uk/id/eprint/142721

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