Trans RINA, Vol 152, Part A4, Intl J Maritime Eng, Oct-Dec 2010 SHIP MOTIONS DURING REPLENISHMENT AT SEA OPERATIONS IN HEAD SEAS
G Thomas, Australian Maritime College, University of Tasmania, Australia T Turner, T Andrewartha1 and B Morris, Defence Science and Technology Organisation, Australia (DOI No: 10.3940/rina.2010.a4.194)
SUMMARY
During replenishment at sea operations the interaction between the two vessels travelling side by side can cause significant motions in the smaller vessel and affect the relative separation between their replenishment points. A study into these motions has been conducted including theoretical predictions and model experiments. The model tests investigated the influence of supply ship displacement and longitudinal separation on the ships’ motions. The data obtained from the experimental study has been used to validate a theoretical ship motion prediction method based on a 3-D zero-speed Green function with a forward speed correction in the frequency domain. The results were also used to estimate the expected extreme roll angle of the receiving vessel, and the relative motion between the vessels, during replenishment at sea operations in a typical irregular seaway. A significant increase in the frigate’s roll response was found to occur with an increase of the supply ship displacement, whilst a reduction in motion for the receiving vessel resulted from an increase in longitudinal separation between the vessels. It is proposed that to determine the optimal vessel separation it is vital that the motions of the vessels are not considered in isolation and all motions need to be considered for both vessels simultaneously.
NOMENCLATURE
[A] Ship added mass matrix [B] Ship damping matrix CL Centreline CoG Centre of gravity [C] Ship hydrostatic stiffness matrix {F} Wave exciting force vector GM Metacentric height (m)
k Wave number (m-1)
LBP Ship length between perpendiculars (m) LCG Longitudinal centre of gravity (m) MS Midships [m]
Ship inertial matrix
RM’ Non-dimensional distance between RAS points VCG Vertical location of the CoG (m) xg xp yg yp zg zp
Longitudinal location of the CoG (m) Longitudinal location of the RAS point (m) Transverse location of the CoG (m) Transverse location of the RAS point (m) Vertical location of the CoG (m)
Vertical location of the RAS point (m)
Δx Point motion in the x direction (m) Δx’ Non-dimensional point motion in the x direction Δy Point motion in the y direction (m) Δy’ Non-dimensional point motion in the y direction Δz Point motion in the z direction (m) Δz’ Non-dimensional point motion in the z direction ηk
{} {}
η η
Displacement in k direction where k = 1-6 (m) Ship acceleration vector
Ship velocity vector { }η Ship displacement vector
ω Wave frequency (rad/sec) ζ
Wave amplitude (m) 1 Currently working for Knud E Hansen, Denmark ©2010: The Royal Institution of Naval Architects A-181 1. INTRODUCTION
Replenishment at sea (RAS) is a critical exercise which allows a naval vessel to remain at sea for extended periods of time and thus provide an ongoing presence, and an immediate response if required, to a developing situation.
In a typical RAS operation, see Figure 1, a naval ship travels side-by-side with a supply ship maintaining constant speed and lateral separation. Hoses and span- wires
are then used to transfer fuel, ammunition, supplies, and personnel between the ships.
Figure
1: Replenishment
at sea operation
between
HMAS SIRIUS and HMAS Toowoomba (photograph courtesy RAN)
During a RAS operation, as the ships travel in close proximity, the presence of the larger vessel can greatly influence the motions of the smaller. This interaction will usually affect the relative separation between the replenishment points on the vessels and hence the tension
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