Fatigue Life Re-Assessment of FSO Spread Mooring System

2017 ◽  
Vol 862 ◽  
pp. 271-277
Author(s):  
Muhammad Irfan
Keyword(s):  
Fatigue Life ◽  
Frequency Domain ◽  
Fatigue Damage ◽  
Summation Method ◽  
Mooring System ◽  
Time Frequency ◽  
Irregular Wave ◽  
Operational Life ◽  
Frequency Domain Approach ◽  
Simple Summation

Re-assessment fatigue life on spread moored system of Floating Storage and Offloading (FSO) vessel moored in irregular wave has been carried out based on hybrid time-frequency domain approach. Previous assessment work result obtained the fatigue life very conservative about thousands of year, whilst existing mooring system was designed for the operational life of 10 years. Different method from previous work was used in fatigue damage calculation approach for undertaking a fatigue mooring analysis in present work. Present works aim to show that the simple summation method used for previous assessment that cause the large variation in fatigue life obtained by comparing different methods of combining fatigue damage. Comparison between the result of fatigue life both previous assessment and present work (re-assessment) of fatigue life are made and discussed.

Frequency Domain Fatigue Analysis for a Unbonded Flexible Riser: Damage Induced by Dynamic Tension

2019 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Zhimin Tan
Keyword(s):  
System Design ◽  
Frequency Domain ◽  
Fatigue Damage ◽  
Deep Water ◽  
Computational Time ◽  
Flexible Riser ◽  
Dynamic Tension ◽  
Irregular Wave ◽  
Unbonded Flexible Riser ◽  
Frequency Domain Approach

Abstract Evaluation of fatigue damage of offshore flexible risers is critical in flexible riser system design. For deepwater application, irregular wave time domain approach is often adopted as the state of practice to avoid excessive conservatism due to its better representation of the stochastic offshore environment. The approach can indeed fully capture the non-linear behaviors of the system at a significant cost of computational time. For example, computational time typically takes over 3∼4 weeks for a deep water free hanging riser system with thousands of fatigue load-cases and the full 3-hour simulations. On the other hand, the same scope of simulation can be completed in frequency domain within day(s), which will enable the designer to accelerate the optimization of riser system design. This paper presents an analysis method in frequency domain for assessing the fatigue damage of tensile armour wires inside the top end fitting (EF), which is induced by dynamic tension variation and often governs the riser service life in deep water applications. A validation measurement is also implemented to ensure the accuracy and practicability of this frequency domain approach in riser system design.

Experimental Investigation on a Point Absorber Moored by Taut Mooring System and Mooring Fatigue Analysis

2020 ◽  
Author(s):  
Sheng Xu ◽  
C. Guedes Soares
Keyword(s):  
Fatigue Damage ◽  
Spectral Methods ◽  
Irregular Waves ◽  
Mooring System ◽  
Wire Ropes ◽  
Irregular Wave ◽  
Point Absorber ◽  
Motion Responses ◽  
Linear Spring ◽  
Rainflow Counting

Abstract In this paper, a taut wire mooring system has been designed consisting of three wire ropes symmetrically arranged. The power take-off system is modelled by a linear spring and a heave plate to simulate the linear damping of the power take-off. A series of regular wave tests in head seas are performed to study the dynamics of the system. Irregular wave tests were then conducted to simulate the system performance in the operational sea states, where the irregular waves are modelled by the Jonswap spectrum. The WEC motion responses and mooring tensions are studied. The short term mooring fatigue damage estimated by different spectral methods are compared to the rainflow counting method. The spectral method for estimating fatigue damage include the Dirlik formula, Jiao-Moan method and Tovo-Benasciutti approach. The accuracy of spectral methods for predicting mooring fatigue damage are discussed.

Critical Evaluation of Frequency-Domain Approach for Fatigue Damage Estimation

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Gašper Vidic ◽  
Marko Nagode
Keyword(s):  
Frequency Domain ◽  
Fatigue Damage ◽  
Input Data ◽  
Critical Evaluation ◽  
High Amplitude ◽  
Damage Estimation ◽  
Accumulated Damage ◽  
Power Spectral ◽  
History Of ◽  
Frequency Domain Approach

Frequency-domain approach for fatigue damage estimation and lifetime prediction of mechanical components is often used for its computational efficiency and the capability to give a synthetic representation of a random process. The problem with the approach is that the input data, the stress power spectral density (PSD), may not include the information about potential small amount of high amplitude cycles which can substantially increase the accumulated fatigue damage. The paper investigates the scatter of the accumulated damage in generated random stress histories and compares them to the results obtained by a frequency-domain approach—the Dirlik method. The results show a possibility of a severe underestimation of accumulated damage when using frequency-domain approach. In case a typical stress, history of a certain mechanical component includes sporadic high amplitude cycles their effect shoud be taken into consideration when using frequency-domain approach.

scholarly journals Comparison of methodological approaches to identify economic activity regularities in transition economy

2011 ◽  
Vol 59 (7) ◽  
pp. 283-292 ◽  
Author(s):  
Jitka Poměnková ◽  
Svatopluk Kapounek ◽  
Roman Maršálek
Keyword(s):  
Frequency Domain ◽  
Economic Activity ◽  
Transition Economy ◽  
Real Data ◽  
Point Of View ◽  
The Czech Republic ◽  
Time Frequency ◽  
Starting Point ◽  
Methodological Approaches ◽  
Frequency Domain Approach

Presented paper focuses on consideration and evaluation of methodical approaches to analyze cyclical structure character of economic activity in transition economy. As a starting point, work in time domain is applied, which is followed in frequency domain approach. Both approaches are viewed from methodical as well as application point of view and their advantage and disadvantage are discussed. Consequently, time-frequency domain approach is added and applied on real data. On the basis of obtained results recommendation is formulated. All discussed methodical approaches are also considered from the perspective of capability to evaluate behaving of business cycle in time of global economic crisis before/after year 2008. The empirical part of the paper deals with data of gross domestic product in the Czech Republic in 1996/Q1–2010/Q2.

scholarly journals Durability Analysis for Coil Spring Suspension Based on Strain Signal Characterisation

2018 ◽  
Vol 7 (3.17) ◽  
pp. 104
Author(s):  
Chin Chuin Hao ◽  
Shahrum Abdullah ◽  
Ahmad Kamal Ariffin ◽  
Salvinder Singh Karam Singh
Keyword(s):  
Fourier Transform ◽  
Fatigue Life ◽  
Frequency Domain ◽  
Time Domain ◽  
Life Prediction ◽  
Energy Content ◽  
Fatigue Life Prediction ◽  
Coil Spring ◽  
Time Frequency ◽  
Strain Signal

This paper aims to predict the durability of an automobile coil spring by characterising the captured strain data. The load histories collected at coil spring are often presented in time domain but time domain cannot provide sufficient information for fatigue life prediction. The objective of this study was to characterise the strain signal in time domain, frequency domain and time-frequency domain for fatigue life prediction. The signal obtained in time domain was used to predict the fatigue life of the coil spring through Rainflow cycle counting technique and models of strain-life relationships. In frequency domain, fast Fourier transform revealed that the frequency components in the strain signal ranged between 0-5 Hz. The frequencies can be further categorised into two ranges: 0-0.3 Hz and 1-2 Hz. Power spectral density confirmed that the frequencies with high energy content were 0-5 Hz and the total energy content in the signal is 4.0872x103 µɛ2. Short time Fourier transform can identify the local time and frequency properties of the signal but it has a limitation in time-frequency resolutions. Wavelet transform can provide a better time-frequency resolutions and it confirmed that the transients in the time domain had frequency range of 1-2 Hz. In summary, this study revealed different possible approaches of signal processing in fatigue life assessment of automotive components as guidance for the selection of suitable approach based on the type of information needed for the analysis.  

Accelerating the fatigue analysis based on strain signal using Hilbert–Huang transform

2019 ◽  
Vol 10 (1) ◽  
pp. 118-132
Author(s):  
Nadia Nurnajihah M. Nasir ◽  
Salvinder Singh ◽  
Shahrum Abdullah ◽  
Sallehuddin Mohamed Haris
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Low Frequency ◽  
Life Assessment ◽  
Distribution Analysis ◽  
Original Signal ◽  
Damage Potential ◽  
Content Type ◽  
Hilbert Huang Transform ◽  
Time Frequency

Purpose The purpose of this paper is to present the application of Hilbert–Huang transform (HHT) for fatigue damage feature characterisation in the time–frequency domain based on strain signals obtained from the automotive coil springs. Design/methodology/approach HHT was employed to detect the temporary changes in frequency characteristics of the vibration response of the signals. The extraction successfully reduced the length of the original signal to 40 per cent, whereas the fatigue damage was retained. The analysis process for this work is divided into three stages: signal characterisation with the application of fatigue data editing (FDE) for fatigue life assessment, empirical mode decomposition with Hilbert transform, an energy–time–frequency distribution analysis of each intrinsic mode function (IMF). Findings The edited signal had a time length of 72.5 s, which was 40 per cent lower than the original signal. Both signals were retained statistically with close mean, root-mean-square and kurtosis value. FDE improved the fatigue life, and the extraction did not affect the content and behaviour of the original signal because the editing technique only removed the minimal fatigue damage potential. HHT helped to remove unnecessary noise in the recorded signals. EMD produced sets of IMFs that indicated the differences between the original signal and mean of the signal to produce new components. The low-frequency energy was expected to cause large damage, whereas the high-frequency energy will cause small damage. Originality/value HHT and EMD can be used in the strain data signal analysis of the automotive component of a suspension system. This is to improve the fatigue life, where the extraction did not affect the content and behaviour of the original signal because the editing technique only removed the minimal fatigue damage potential.

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