About | Research | Events | People | Reports | Alumni | Contact | Home
 |
30 January - 3 February 2012
|
|
Marin
Structural integrity of marine structures
Hannes Bogaert- Hydro-Structural Services , Marin
Operators of ships and offshore structures face the responsibility of maximising
the operational window
while taking care of the safety onboard. Periodic
inspections help the operator to assess if the structure is still in one piece
and whether repairs are required. Continuous monitoring of the structure’s
response as motions and stresses, is increasingly used to assist the operator
in this. By comparing the measured responses to the design limits, the operator
can not only identify when the structure will fail, but can also prevent that it
fails. Today, we are further increasing the effectiveness of the operator by
linking inspection and continuous monitoring to design tools. This enables the
operator to safeguard more than the inspected or monitored locations and to
better assess new operational conditions.
Using the design tools during operations requires that we gradually update the design conditions (i.e. the input for the tools) by the actual conditions. Moreover, it requires that we gradually update the design characteristics (i.e. the design tool parameters) by the actual characteristics of the structure. And here lies the challenge of this project.
The major part of the tool parameters are described by Response Amplitude Operators (RAO). Each RAO presents the ratio between the structure’s response and the wave height as function of the wave period and the wave direction. Long crested uni-directional waves are assumed. The responses are the motions in the six degrees of freedom, the hull girder bending loads, the local stresses, etc. To update the RAO’s we perform long-term wave and structural response measurements during operation. The waves during operation however propagate in multiple directions at the same time, are short crested, and are measured at a distance from the ship or offshore structure. The response measurements are therefore not unambiguous linked to the wave measurement by RAO’s.
Objectives
MARIN hopes that SWI can help to improve the physical and mathematical understanding on how to
1. gradually update a tool parameter described as a RAO’s by long-term measurements assuming ‘perfect waves’, i.e. long crested uni-directional waves with a wave direction varying in time. The tool parameter might be non-stationary.
2. adjust the update technique for the fact that actual waves are ‘not perfect’, i.e multi-directional, short crested and measured at a distance from the ship or offshore structure, however maximizing the fact that there are long term measurements.
Measurement data and design RAO’s will be made available for this project.