Efficient Probabilistic Fatigue Analysis of a Riser Suspended and Moored by Chains

2015 ◽  
Author(s):  
Juan S. M. Giraldo ◽  
Luis V. S. Sagrilo ◽  
Claudio M. S. Dantas
Keyword(s):  
Numerical Simulation ◽  
Fatigue Damage ◽  
Asymptotic Approximation ◽  
Fatigue Analysis ◽  
Direct Integration ◽  
Brute Force ◽  
Offshore Structure ◽  
Huge Number ◽  
Stress Spectrum

Fatigue analysis of an offshore structure usually requires the numerical simulation of a huge number of loading cases to compute the long-term integral associated to the accumulated fatigue damage. Papadimitriou et al. [1] and Low and Cheung [2] proposed two distinct approaches to solve the long-term fatigue damage more efficiently. These methods are known as Asymptotic Approximation Method and Perturbation Method, respectively. This paper investigates the efficiency of these two methods in the fatigue analysis of the steel pipe of a riser suspended and moored by chains (RSAA). Since there is an analytical solution for the stress spectrum of this riser, both time and frequency domain fatigue assessments approaches are considered. The accuracy and computational efficiency of the aforementioned methods are compared with the “brute force” direct integration methodology.

Direct Calculation of Fatigue Damage of Ship Structure Details

2011 ◽  
Author(s):  
Zhiyuan Li ◽  
Jonas W. Ringsberg
Keyword(s):  
Fatigue Damage ◽  
Time Domain ◽  
Direct Calculation ◽  
Fatigue Analysis ◽  
Fe Model ◽  
Stress Concentration Factors ◽  
Rainflow Counting ◽  
Global And Local

Fatigue assessment of ships using the direct calculation approach has been investigated by numerous researchers. Normally, this approach is carried out as either a global model analysis, or as a local model structural analysis. The current investigation presents a case study of a container vessel where the global and local analyses procedures are combined. A nonlinear time-domain hydrodynamic analysis followed by a global FE analysis is employed to screen for the most severe locations of the global ship’s hull with regard to fatigue damage. Once these locations have been identified, a sub-modelling technique is employed to transfer global loads from the global FE model to local FE models that have high resolution of elements for local structure details. Results from a selection of local FE model simulations are presented. Stress concentration factors at four critical locations are calculated and compared with values recommended by classification guidelines. Results are presented from a short-term fatigue analysis which has been carried out using the rainflow counting method. Finally, a long-term fatigue analysis is performed in time-domain using a designed wave scatter diagram of representative sea states.

A Method of Fatigue Damage Analysis for Sandwich Panels on Ship

2010 ◽  
Vol 452-453 ◽  
pp. 849-852
Author(s):  
Qi Chao Xue ◽  
Guang Ping Zou
Keyword(s):  
Fatigue Damage ◽  
Sandwich Structure ◽  
Sandwich Panels ◽  
Damage Analysis ◽  
Short Term ◽  
Stress Spectrum ◽  
Fatigue Damage Analysis ◽  
Distribution Of Stress ◽  
The Waves

A method of fatigue damage analysis for sandwich panels on ship is studied in this paper. When ship is navigating on the sea, the waves that ship encounters can be regarded as a stochastic process. And responses of ship movement can also be regarded as a series of stochastic spectrums. By using of finite element method, loads spectrums of inner ship structures in different sea conditions can be obtained. Then short term or long term distribution of stress range can be determined. Residual stiffness modal is used to describe the damage of sandwich panels under fatigue loads. And fatigue damage variable D is defined based on stiffness degration. An integral equation to calculate fatigue damage under loads spectrum is constructed to describe the damage of ship sandwich structure in long term and short term stress spectrum distributions.

Closed-Form Spectral Fatigue Analysis for Compliant Offshore Structures

1988 ◽  
Vol 32 (04) ◽  
pp. 297-304
Author(s):  
Y. N. Chen ◽  
S. A. Mavrakis
Keyword(s):  
Closed Form ◽  
Fatigue Damage ◽  
Computational Cost ◽  
Power Spectra ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Cumulative Fatigue Damage ◽  
High Computational Cost

Spectral fatigue analysis frequently has been applied to welded joints in steel offshore structures. Although, on the theoretical basis, the spectral formulation holds certain advantages over other formulations such as the discrete, design wave type of analysis, numerical methods developed on that basis generally suffer from the shortcomings of lack of precision and high computational cost. This paper synthesizes the uncertainties resulting from modeling errors that are regarded heretofore as unavoidable in an analysis. Such errors are traced to the approximations introduced in handling of wave data, in numerical integration of the response power spectra, and in the integration that leads to the determination of cumulative fatigue damage. To each of these sources of modeling error, a transparent, closed-form method is proposed which not only eliminates the potential errors but, surprisingly, improves the computational efficiency many times. The sensitivity of fatigue damage upon the variability of the shape parameter due to variability of wave environment for the so-called simplified analysis utilizing an idealized mathematical long-term probability density function (for example, the Weibull distribution) is also discussed.

Studies on Dynamic Response of Subway Tunnels with Initial Defect under Long-Term Train Loads

2012 ◽  
Vol 226-228 ◽  
pp. 1005-1009
Author(s):  
Fei Dong ◽  
Jun Dong ◽  
Wei Ze Sun
Keyword(s):  
Numerical Simulation ◽  
Dynamic Response ◽  
Fatigue Damage ◽  
Structural Damage ◽  
Side Wall ◽  
Subway Construction ◽  
Subway Tunnels ◽  
Initial Cracks ◽  
Deterioration Characteristics

Based on the background of a subway construction project, deterioration characteristics of the existed subway tunnels under long-term train loads is studied by using the method of stiffness discount which could reflect fatigue damage of the structure. Firstly, dynamic response of the tunnel with initial defects caused by approaching construction under long-term train loads is analyzed according numerical simulation, and some results under different degrees of fatigue are obtained. Then, numerical results of acceleration responses at such different points as the upper vault, the side wall and the bottom of tunnels in two directions, are compared with each other while the train loads are applied at the left tunnel, especially under three different stiffness. Our investigation shows local structural damage in the position with initial cracks will be caused by a high cycle stress although there are fewer influences of stiffness changes on dynamic response of tunnels.

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

2020 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Zhimin Tan
Keyword(s):  
Tensile Stress ◽  
Frequency Domain ◽  
Fatigue Damage ◽  
Time Domain ◽  
Time History ◽  
Domain Analysis ◽  
Fatigue Analysis ◽  
Stress Spectrum ◽  
History Of ◽  
Frequency Domain Approach

Abstract The service life of flexible risers is a vital design parameter in offshore field development. The standard approach to calculate fatigue life is the nonlinear time-domain analysis. The approach uses time history of riser responses in local structure assessment to get the fatigue damage of tensile layers. Another approach is the linearized frequency-domain analysis. Instead of using time history of stress and rainflow counting technique, the approach uses stress spectrum and empirical mathematical terms to estimate the fatigue damage. The frequency domain approach is significantly faster. However, due to the whole system being linearized, the latter usually produces different results and is considered to be less accurate than the time domain approach. To address this issue, Baker Hughes previously developed an approach which uses the frequency domain technique as base solution and calibration factors from limited time domain cases. The approach is limited to tensile wires at the end fitting entrance where tension and tensile stress is directly linked. In this paper, a similar approach is proposed to be applied for tensile fatigue at all regions, whose tensile stress are induced by a combination of tension, pressure, bending and friction between layers. Since tensile stress is not directly related to any single riser response, the stress spectrum is predicted by using a transfer function. With the predicted stress spectrum, the fatigue damage of each case is calculated with Dirlik’s method and SN curves. The paper summarizes the development of the hybrid frequency domain approach. The fatigue damage of risers from several projects are acquired with both time domain and frequency domain approaches. The approach is significantly faster than traditional time domain approach and produces conservative results. Furthermore, discussions are made on options to improve the approach and reduce the conservatism in the frequency domain fatigue analysis.

Investigations Into Uncertainties in Fatigue Damage During Transport Phase for Topside Structures

2018 ◽  
Author(s):  
Suji Zhu ◽  
Helene Høgseth Haaheim ◽  
Marc Lefranc
Keyword(s):  
Fatigue Damage ◽  
Oil And Gas ◽  
Fatigue Analysis ◽  
Simplified Approach ◽  
Factors Influencing ◽  
Inertia Forces ◽  
Transport Phase

Up to now, the uncertainties in the fatigue utilization during operation (long-term, typical 20 to 30 years) phase have been widely investigated for various oil and gas installations while limited attentions have been paid to the fatigue damage during the transport phase. In normal, the fatigue damage during the transport phase is assumed to contribute limited proportions (for example, less than 5%) of the total fatigue damage for the whole life since the transport duration is at most several months. However, as the size of oil and gas installations increases, the fatigue damage during the transport phase may increase noticeably considering the inertia forces in moderate or severe sea states. During the transport, the weather encountered may deviate significantly from the long-term statistical values. It becomes crucial to determine the uncertainties in the calculated fatigue damage during the transportation phase. Nowadays, the uncertainties are mainly accounted for using Design Fatigue Factor (DFF) while the value of DFF may be different in different standards. In this paper, the fatigue damage for a topside module during the transport phase is studied. Three different vessels are to be used for comparison purpose. The uncertainties due to the sea states encountered are focused. Simplified approach is adopted to investigate the factors influencing fatigue damage. In addition, the calculated fatigue damage is also compared with the fatigue damage based on simplified fatigue analysis.

Hybrid Fatigue Analysis Method for Railway Carbody Structure

2008 ◽  
Vol 44-46 ◽  
pp. 733-738 ◽  
Author(s):  
Bing Rong Miao ◽  
Wei Hua Zhang ◽  
Shou Ne Xiao ◽  
Ding Chang Jin ◽  
Yong Xiang Zhao
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Hybrid Method ◽  
Dynamic Stress ◽  
Stress Test ◽  
Fatigue Analysis ◽  
Railway Vehicle ◽  
Analysis Method ◽  
Structure Dynamic ◽  
Multi Body

Railway vehicle structure fatigue life consumption monitoring can be used to determine fatigue damage by directly or indirectly monitoring the loads placed on critical vehicle components susceptible to failure from fatigue damage. The sample locomotive carbody structure was used for this study. Firstly, the hybrid fatigue analysis method was used with Multi-Body System (MBS) simulation and Finite Element Method (FEM) for evaluating the carbody structure dynamic stress histories. Secondly, the standard fatigue time domain method was used in fatigue analysis software FE-FATIGUE and MATLAB WAFO (Wave Analysis for Fatigue and Oceanography) tools. And carbody structure fatigue life and fatigue damage were predicted. Finally, and carbody structure dynamic stress experimental data was taken from this locomotive running between Kunming-Weishe for this analysis. The data was used to validate the simulation results based on hybrid method. The analysis results show that the hybrid method prediction error is approximately 30.7%. It also illustrates that the fatigue life and durability of the locomotive can be predicted with this hybrid method. The results of this study can be modified to be representative of the railway vehicle dynamic stress test.

Downtime Analysis Techniques for Complex Offshore and Dredging Operations

2004 ◽  
Author(s):  
Remmelt J. van der Wal ◽  
Gerrit de Boer
Keyword(s):  
Wind Waves ◽  
Weather Forecast ◽  
Offshore Structures ◽  
Operational Mode ◽  
Offshore Structure ◽  
Hydrodynamic Models ◽  
Time Step ◽  
Made In

Offshore operations in open seas may be seriously affected by the weather. This can lead to a downtime during these operations. The question whether an offshore structure or dredger is able to operate in wind, waves and current is defined as “workability”. In recent decades improvements have been made in the hydrodynamic modelling of offshore structures and dredgers. However, the coupling of these hydrodynamic models with methods to analyse the actual workability for a given offshore operation is less developed. The present paper focuses on techniques to determine the workability (or downtime) in an accurate manner. Two different methods of determining the downtime are described in the paper. The first method is widely used in the industry: prediction of downtime on basis of wave scatter diagrams. The second method is less common but results in a much more reliable downtime estimate: determination of the ‘job duration’ on basis of scenario simulations. The analysis using wave scatter diagrams is simple: the downtime is expressed as a percentage of the time (occurrences) that a certain operation can not be carried out. This method can also be used for a combination of operations however using this approach does not take into account critical events. This can lead to a significant underprediction of the downtime. For the determination of the downtime on basis of scenario simulations long term seastate time records are used. By checking for each subsequent time step which operational mode is applicable and if this mode can be carried out the workability is determined. Past events and weather forecast are taken into account. The two different methods are compared and discussed for a simplified offloading operation from a Catenary Anchor Leg Mooring (CALM) buoy. The differences between the methods will be presented and recommendations for further applications are given.

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