Date of Award

2014

Degree Type

Thesis

Degree Name

Master of Science in Ocean Engineering

Department

Ocean Engineering

First Advisor

Jason M. Dahl

Abstract

The majority of floating AtoN maintained by the U.S. Coast Guard are affixed to the sea bed through use of a chain and a large concrete block also known as a sinker. As a buoy moves through a wave cycle, the buoy chain also moves. This movement causes friction between the links known as interlink wear, but it also results in wear from the surrounding environment. A mooring chain is characterized into three different sections, the riser, chafe and bottom. The chafe section of chain is where most of the wear is found and more often than not, the reason a buoy must be serviced on a regular basis. This thesis will focus on the interlink wear within the chafe section of the chain on a U.S. Coast Guard navigational buoy mooring.

With the total motion of the chain, chain size and material type are known, tribology was used to determine the wear rate of the chain. Since determining the wear rate analytically would be very difficult, empirical based testing was used. An experiment using AISI 1022 hot rolled steel chain, a variable speed motor and various parts was constructed. The device moved the chain in a set vertical direction along a slide resulting in a simulated regular wave motion. Stops at different time intervals were made to measure chain weight and interlink wear. This data was plotted and a curve constant, K, was determined as a function of time which would be used in the program. The experimental results were compared to tabulated and analytical results to find that there was not much variation between each result. Pi parameter regressions were used to help with scaling results to different materials and chain dimensions.

A MATLAB based computer program was written to predict when a buoy mooring would require servicing through a chain wear algorithm which will optimize buoy mooring service intervals and reducing cost to maintain each aid. The program was found to estimate chain wear within 2 percent of observed on in service buoys.

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