Output-Only Structural Health Monitoring for Deepwater Risers: Experimental Study of Wavelet Modified SOBI and Distributed Force Index Algorithm

TLDR

Risers serve as conduits between subsea wellheads and drilling or production platforms and are among the most critical and vulnerable components of deepwater floating platforms. This study proposes a global structural health monitoring system for deepwater risers that employs a wavelet‑modified second‑order blind identification (WMSOBI) method combined with a distributed force change (CDFC) index to fill the existing gap. WMSOBI yields reliable time‑frequency modal properties even under large damping and under‑determined conditions, and the authors conducted experiments on a suspended pipe to demonstrate the approach. The CDFC index derived from WMSOBI‑extracted modal data accurately locates and quantifies single and multiple crack damage, with both numerical simulations and experimental tests confirming the effectiveness of the proposed SHM system.

Abstract

Risers are the conduits between the subsea wellhead and the drilling/production platform for development, production, gas lift or water injection purposes, which are also one of the most important and the most vulnerable components for deepwater floating platforms. To address the lack of appropriate global structural health monitoring (SHM) system for deepwater risers, this paper proposes a time-frequency domain approach using a wavelet modified second order blind identification (WMSOBI) method and combined distributed force change (CDFC) index. WMSOBI provides a reliable time-frequency domain identified modal properties of riser systems, even with large damping and under-determinate conditions. In addition, CDFC index generated from modal properties extracted by WMSOBI can accurately identify the damage location and damage level for both single and multiple crack scenarios. Details of experiments conducted on suspended pipe are presented. Both numerical and experimental verification are presented to validate the effectiveness of the proposed WMSOBI/CFDC algorithm and SHM system.