Stinger monitoring system

Abstract

A stinger is a steel space frame structure, used on pipe-lay vessels, to support the weight of a suspended pipeline. A stinger is highly fatigue loaded due to environmental loads, vessel motions and variable pipe loads. In the design phase, predictions for the structural behaviour of the stinger were made. However, inspection history showed discrepancies between the design phase and reality. A stinger monitoring system was proposed to provide a solution for this problem. The goal of the thesis was formulated as follows: Design of an optimised sensor placement method for a stinger monitoring system to localise and quantify damage. A method based on the vibration characteristics of a stinger model was chosen for damage localisation and quantification. This method correlates the measured modal property changes with analytical modal property changes to identify damaged members and to estimate the damage extent in these members. A sequential sensor placement method was applied to determine the sensor locations contributing most to the modes of vibration of the stinger model. The proposed method can accurately localise damage for damage situations with one damaged member. For damage situations with multiple damaged members, the method is able to correctly identify one of the damaged members. To identify the other damaged members, a modification of the method was proposed. On the condition of a damage threshold, this modified method is able to localise multiple damaged members in a selected number of damage situations. The damage quantification method was able to give a good estimate of the damage extent.