Accurate Prediction of Fatigue Life under Random Loading

2012 ◽  
Vol 61 (10) ◽  
pp. 853-859 ◽  
Author(s):  
Norio TAKEDA ◽  
Tomohiro NARUSE
Keyword(s):  
Fatigue Life ◽  
Accurate Prediction ◽  
Random Loading

A Method for Fatigue Analysis of Pipelines on Topsides of FPSO Systems

2005 ◽  
Author(s):  
Pol Spanos ◽  
Alba Sofi ◽  
Juan Wang ◽  
Berry Peng
Keyword(s):  
Fatigue Life ◽  
Random Vibration ◽  
Equations Of Motion ◽  
Plug Flow ◽  
Fatigue Curve ◽  
Sea Waves ◽  
Random Loading ◽  
Euler Beam ◽  
Stress Spectrum ◽  
The Galerkin Method

Pipelines located on the decks of FPSO systems are exposed to damage due to sea waves induced random loading. In this context, a methodology for estimating the fatigue life of conveying-fluid pipelines is presented. The pipeline is subjected to a random support motion which simulates the effect of the FPSO heaving. The equation of motion of the fluid-carrying pipeline is derived by assuming small amplitude displacements, modeling the empty pipeline as a Bernoulli-Euler beam, and adopting the so-called “plug-flow” approximation for the fluid (Pai¨doussis, 1998). Random vibration analysis is carried out by the Galerkin method selecting as basis functions the natural modes of a beam with the same boundary conditions as the pipeline. The discretized equations of motion are used in conjunction with linear random vibration theory to compute the stress spectrum for a generic section of the pipeline. For this purpose, the power spectrum of the acceleration at the deck level is determined by using the Response Amplitude Operator of the FPSO hull. Finally, the computed stress spectrum is used to estimate the pipeline fatigue life employing an appropriate S-N fatigue curve of the material. An illustrative example concerning a pipeline simply-supported at both ends is included in the paper.

Fatigue Analysis on Key Components of Semi-Submersible Platform

2010 ◽  
Author(s):  
Lei Cui ◽  
Jia-nan Xu ◽  
Yong He ◽  
Wei-liang Jin
Keyword(s):  
Fatigue Life ◽  
Energy Spectrum ◽  
Stress Responses ◽  
Stress Transfer ◽  
Local Model ◽  
Random Wave ◽  
Wave Loads ◽  
Random Loading ◽  
Fatigue Stress ◽  
Model Platform

Fatigue damage is one of the main reasons of the failure of Semi-Submersible platform. As the complex of random loading, it is difficult to analyze fatigue life accurately and determine the sensitivity of parameters. In this paper, the fatigue life on key-components of semi-submersible platform is analyzed with Spectral-based analysis method. Firstly, the stress responses of whole model platform under the random wave loads are calculated. The calculation results of whole model platform for cut-boundary interpolation are used in local model to calculate the key-component stress responses of local model. Generating the fatigue stress energy spectrum by scaling the wave energy spectrum and the complex fatigue stress transfer function in detail local model is described next. The stress response of short-term sea-state is assumed to obey Rayleigh distribution, and the spectral moments are calculated. Finally, the fatigue life of key components is analyzed according to S-N curve and Palmgren-Miner’s rule. The results show that the fatigue life of the connection meets the specification requirements, and the key components are the fatigue sensitive areas of semi-submersible platform.

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