3D Scanning of Corroded Mooring Chain

Abstract

This thesis is concerned with mooring line failure and 3D representations of corroded chain surfaces. Equipment for making such representations have been evaluated through a feasibility study carried out at NTNU.

An ATOS III sensor was used to measure heavily corroded chain surfaces. Measuring procedures have been evaluated and best practice has been suggested. The produced output was a dense point cloud, mapping an area of approximately 15500 mm^2.

The point cloud was post processed in Geomagic Studio 14 and ANSYS ICEM CFD. A surface model processed for inspection routines, was created. Also a model representing a block with a single cavity was made. This was compatible with the software Abaqus.

A submodeling analysis was carried out in Abaqus, to simulate a cavity on the surface of a chain link in static tension. Good conformity was found in the stress response of the edge regions. It was concluded that the submodel was able to recreate the conditions in a chain link surface. Consistency in the location of the critical area of the model was observed. Convergence of the maximum principle stress in the critical area was not proven. The smoothing routine and insufficient minimum size of the elements in the mesh was pointed out as the most plausible explanations.

The use of submodeling analysis in further study is highlighted as a good method for evaluating worst case scenarios considering cavities on the surface of chain links. Advices considering efficiently evaluation of convergence and mesh requirements have been given.

A literature study with main focus on mooring system components and mooring line failure was presented. The historical development considering mooring line failure during the last 20 years was illustrated through statistical data.