Nonlinear wave interactions with multiple bodies in close proximity
Author(s)
Peric, Milena
Type
Thesis
Abstract
This thesis describes the interaction of waves with multiple bodies in close proximity.
The case of two-dimensional fixed bodies is first considered, where large
wave excitation is found to occur within the gap between the two bodies at the
so-called resonance frequency. The width of the gap is identified as the most important
factor in determining this frequency; an increase in the gap width leading
to a decrease in the resonance frequency. Subsequently, the effect of the motion
of one of the bodies (with a single degree of freedom) is investigated using a newly developed floating-body application of the boundary element method. In the floating-body case, the resonance frequency is found be higher than in the
fixed-body equivalent. In addition, a large amplification of the nonlinear water
surface elevation within the gap is identified.
In order to determine whether the observations within the two-dimensional
study can be applied to the practical case of side-by-side offloading of Liquid
Natural Gas (LNG), similar investigations are undertaken in a three-dimensional
analysis. The latter involves both numerical and experimental studies. The three-dimensional
studies confirm the effects identified in the two-dimensional analysis;
specifically the effects of the gap width, the motion of one of the bodies, and the
nonlinear effects arising within the gap are all clearly established. Furthermore,
consideration of both beam-sea and head-sea incident wave conditions eliminates
the orientation of the bodies relative to the incident wave direction as a key factor
in determining the resonance frequency. Finally, consideration of the motion of
the bodies shows that some unexpected higher order motion of the moored body
arises when the two bodies have significantly different hydrodynamic properties.
As a result, it is concluded that the numerical modelling of side-by-side offloading
must be fully nonlinear, incorporate the body motion and include the forcing of
the fenders and the mooring lines.
The case of two-dimensional fixed bodies is first considered, where large
wave excitation is found to occur within the gap between the two bodies at the
so-called resonance frequency. The width of the gap is identified as the most important
factor in determining this frequency; an increase in the gap width leading
to a decrease in the resonance frequency. Subsequently, the effect of the motion
of one of the bodies (with a single degree of freedom) is investigated using a newly developed floating-body application of the boundary element method. In the floating-body case, the resonance frequency is found be higher than in the
fixed-body equivalent. In addition, a large amplification of the nonlinear water
surface elevation within the gap is identified.
In order to determine whether the observations within the two-dimensional
study can be applied to the practical case of side-by-side offloading of Liquid
Natural Gas (LNG), similar investigations are undertaken in a three-dimensional
analysis. The latter involves both numerical and experimental studies. The three-dimensional
studies confirm the effects identified in the two-dimensional analysis;
specifically the effects of the gap width, the motion of one of the bodies, and the
nonlinear effects arising within the gap are all clearly established. Furthermore,
consideration of both beam-sea and head-sea incident wave conditions eliminates
the orientation of the bodies relative to the incident wave direction as a key factor
in determining the resonance frequency. Finally, consideration of the motion of
the bodies shows that some unexpected higher order motion of the moored body
arises when the two bodies have significantly different hydrodynamic properties.
As a result, it is concluded that the numerical modelling of side-by-side offloading
must be fully nonlinear, incorporate the body motion and include the forcing of
the fenders and the mooring lines.
Date Issued
2012
Date Awarded
2012-03
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Swan, Chris
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)