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research-article

An Empirical Procedure for Fatigue Damage Estimation in Instrumented Risers

[+] Author and Article Information
C. Shi

School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shangdong 266580, P.R. China
shichen2004@hotmail.com

L. Manuel

Department of Civil, Architectural, and Environment Engineering, University of Texas, Austin, TX 78712, USA
lmanuel@mail.utexas.edu

1Corresponding author.

ASME doi:10.1115/1.4035303 History: Received July 01, 2016; Revised November 10, 2016

Abstract

Vortex-induced vibration (VIV) can lead to significant fatigue damage accumulationin deepwater marine risers. In order to assess the effects of VIV and to ensure riser integrity, field monitoring campaigns are often conducted wherein the riser response is recorded by a few data sensors distributed along the length of the riser. It is possible to empirically estimate the fatigue damage at “key” critical fatigue-sensitive locations where sensors may not beavailable as part of the spatially distributed discrete measurements. In thisstudy, two empirical techniques—Proper Orthogonal Decomposition (POD) and Weighted Waveform Analysis (WWA)—are sequentially applied to the data; together, they offer a novel empirical procedure for fatigue damage estimationin an instrumented riser. The procedures are briefly described as follows: first, POD is used to extract the most energetic spatial modes of the riser response from the measurements. Often, only a few dominant POD modes preserve most of the riser motion kinetic energy; other modes maybe considered less important. Identified POD mode shapes are discrete as they are defined only at the available sensor locations. Accordingly, a second step in the proposed procedure uses WWA to express each dominant POD mode as a series of riser natural modes that are continuous spatial functions defined over the entire riser length. Based on the above empirically identified modal information, the riser response over the entire length is reconstructed in reverse—i.e., compose identified natural modes into the POD modes and,then, assemble all these dominant POD modal response components into the derived riser response. The POD procedure empirically extracts the energetic dynamic response characteristics without any assumptions and effectivelycleans the data of noisy or less important features; this fundamental application of WWA is used to identify dominant riser natural modes—all this is possible using the limited number of available measurements fromsensor locations. Application of the entire procedure is demonstrated usin gexperimental data from the Norwegian Deepwater Programme (NDP) model riser.

Copyright (c) 2016 by ASME
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