Experimental ambient vibration-based structural health monitoring in top-tensioned risers

Risers are crucial components in offshore production systems, and failure of a riser can potentially cause catastrophic damage to the environment and significant loss of production. The early identification of damage in a riser is essential to prevent failure from occurring, and vibration-based structural health monitoring (SHM) methods may be a viable means of achieving this. This study seeks to determine if there is merit to the application of vibration-based SHM methods to identify damage in top-tensioned risers under wave loading. To that end, two SHM methods are proposed and applied to experimental data obtained from a riser model placed in a wave flume with damage simulated as pre-tension loss. The proposed methods utilize the shift of the first natural frequency of the riser for damage identification. In the first method, the natural frequency is obtained from a frequency response function relating the water surface elevation and acceleration response of the riser model. In the second method, an ambient response analysis method is applied. Both methods are able to identify the natural frequency shifts and there is potential for detection and severity assessment of damage.