Seabed scour induced by twin-propeller ships / Yew Wan Tian

Yew, Wan Tian (2017) Seabed scour induced by twin-propeller ships / Yew Wan Tian. PhD thesis, University of Malaya.

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Abstract

To date, higher power ships are extensively used in order to fulfil the maritime trading demand. The resulting high velocity thrust produced by ship’s propellers or side thrusters has seriously eroded the seabed. Ship-Twin-Propeller (STP) is a ship equipped with two propellers. It has improved powering system, handling system, ship stability, and ability to propel the ship faster as compared to single ships. These advantages have increased the demand for STP among the marine traders for higher profitability and efficiency. This study involves experimental and virtual simulation works. Laboratory experiments were designed to investigate the axial velocity profile of selected rotating STP and the resulting scouring actions; whereas, the Computational Fluid Dynamic (CFD) model simulation was used to observe and estimate scouring pattern. The existing theory and experimental results were mostly derived from plain jet and single rotating propeller. This study has enhanced the understanding on the scour mechanisms and relationships of STP’s velocities impingement on the seabed. The asymptotic scour induced by STP profile was defined in four stages, which are (i) initial stage, (ii) developing stage, (iii) merging stage and (iv) asymptotic stage. An equation is proposed to relate between the parameter, namely the densimetric Froude number, the clearance ratio and the reference time scale for the prediction of maximum scour depth and also the maximum scour location. The proposed equations were found to be highly correlated with the observed parameters. Moreover, the proposed CFD and experiment model have given representative data in graphical method to simulate the scouring pattern at different sections for better scour estimation and visualisation. Therefore, it is able to assist design engineers and port authorities in designing the protection structure against scour erosion. Moreover, this will also help in designing the bathymetry level, so that the designed level would be maintained to minimise the dredging or filling sediments costs.

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