Erosion of a granular bed at a quay wall by a ship's screw wash

Abstract

The design of a propeller in relation to the performance of a ship has long been a matter of great interest, but the study of the characteristics of the wash produced, and its erosive power, was only recently given consideration. This experimental research was carried out with a view to investigate the behaviour of a ship's propeller wash influenced by a lateral quay wall. However, a comparison to the corresponding jet in an open water situation was not overlooked.

Some existing equations relevant to the unconfined propeller wash were refined as they have frequently to be used. The properties of the confined jet with reference to quay wall clearance were studied using two propellers of quite different characteristics. It was observed that significant influence of the wall on the jet occurred only in its zone of established flow for the configurations tested. Equations for the decay of maximum and centreline velocities were derived with respect to wall proximity in the zone of established flow. The location of the point of maximum velocity at any section in the confined jet was also determined.
A relationship for the location of the maximum velocity profiles taken transverse to the propeller axis was established with reference to quay wall distance. Formulae were developed for the velocity distribution in these profiles with relation to quay wall clearance.

Equations were developed for the velocity distributions on verticals through the propeller axis. These were then related to quay wall separation. Turbulence intensities in the confined situation was also considered.

The influence of a parallel quay wall on the scouring of granular bed material by propeller jets was investigated in detail.

The existing equation for the temporal development of maximum scour depth was improved for the unconfined situation. Equations were proposed to predict changes in this scour depth due to the presence of a quay wall. Formulae were also derived to determine scour depths at the toe of the quay wall. The development of scour in a confined situation was investigated with respect to time and distance to the wall.

Equations are proposed which determine the magnitude and location of maximum scour depth with reference to time in this laterally confined situation. The velocity distributions within scour pits arrested at different stages in their development were studied for both unconfined and confined washes to give an insight into the development of the eroded profile .

Date of Award	Jul 1993
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Harold Johnston (Supervisor) & G.A. Flynn (Supervisor)