Designing Wave Attenuation Solutions using Hydro-Structural Modelling in ComFLOW to reduce Free Surface Motions within a Flooded Well-Dock of an existing Landing Platform Dock

Master thesis (2024)

Authors

D.M. Mehlbaum Mechanical Engineering

Contributors

P.R. Wellens Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering (mentor)
G.H. Keetels Offshore and Dredging Engineering - Mechanical, Maritime and Materials Engineering (mentor)
A.D. Boon Ship Hydromechanics - Mechanical, Maritime and Materials Engineering (mentor)
R.W. Bos (mentor)
Faculty
Mechanical Engineering
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Published Date

18-07-2024

Language

English

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Faculty

Mechanical Engineering

Abstract

A Landing Platform Dock (LPD) facilitates amphibious operations by allowing landing vessels such as the Landing Craft Vehicle Personnel (LCVP) and Landing Craft Utility (LCU) to embark and disembark from its internal flooded well-dock. The smooth transition of these landing vessels is critical, but can be hindered by wave motions (i.e. sloshing) within the well-dock, making safe embarking and disembarking more difficult.

Existing literature mainly describes wave motions within a well-dock, but does not address how to minimise these motions. This thesis aims to develop a preliminary design to reduce wave energy entering the dock by implementing an optimised wave attenuation solution.

ComFLOW is used to observe that wave motions inside the well-dock are highly non-linear and correspond to the LPD’s oscillation period. The wave motions within the dock are caused by a drop in water level near the well-dock entrance. This causes waves to roll into the dock. In shallow water conditions like in the well-dock, the propagating waves hereby show amplitude dispersion and wave breaking.

Using a system engineering approach, a bottom-hinged pitching flap was found to be ideal for wave attenuation in shallow water conditions. The flap’s attenuation performance was examined using ComFLOW by adjusting design parameters such as: mass, center of gravity, length and mechanical damping.

It was found that high-period waves with high wave heights fully couple dynamically with the flap, resulting in several outcomes. First, the flap follows the wave frequency, resulting in sub-optimal energy dissipation with use of radiation damping. Second, tuning the flap’s natural period to match the incoming wave period, increases pitching angles but reduces angular velocity, leading to decreased wave attenuation. Third, lowering the centre of gravity increases the restoring moment and angular velocity. This results in enhanced energy dissipation of higher-order wave components. Fourth, increasing the flap’s length improves wave attenuation due to enhanced reflection and radiation damping. Fifth, adding mechanical damping decreases attenuation performance, likely because the reduction in angular velocity worsens the energy dissipation effect for higher-order wave components. This research revealed that the best performing solution, with low a centre of gravity, attenuates 28.7% of wave energy entering the well-dock. Furthermore, optimising the flaps natural period to the incoming wave period was less effective, attenuating only 19.7% of the wave energy.