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.

Time Domain Fatigue Life Analysis of Offshore Jacket Structure

2019 ◽  
Author(s):  
Yan Wei Wu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time Domain ◽  
Offshore Wind ◽  
Support Structure ◽  
Structural Fatigue ◽  
Long Time ◽  
Fatigue Life Analysis ◽  
Stress Concentration Factors ◽  
The Time Domain

Abstract Offshore wind system encountered wind, wave, current, soil, and other environmental loads. The support structure is randomly loaded for a long time, which is more likely to cause fatigue damage. In this paper, the NREL 5MW wind turbine and OC4 jacket support structure is selected to perform the time domain fatigue analysis. Commercial software Bladed and SACS are used to perform the required structural responses and fatigue strength calculations. The Stress Concentration Factors (SCF) and S-N curves for the stress calculations of tubular joints are adopted based on the recommendation of DNV GL guidelines. The magnitude of the stress variation range and the corresponding number of counts are obtained by using the rain-flow counting algorithm. Finally, the Palmgren-Miner’s rule is adopted to calculate the cumulative damage ratio and the fatigue life can then be estimated. Fatigue damage ratio and structural fatigue life of each joint during 20 years of operation period are evaluated.

Long-Term Fatigue Analysis of Deepwater Risers in the Time Domain

2014 ◽  
Author(s):  
Yidan Gao ◽  
Ying Min Low
Keyword(s):  
Time Domain ◽  
Time Domain Analysis ◽  
Fatigue Analysis ◽  
Sea State ◽  
Need To Evaluate ◽  
Nature Of Time ◽  
The Time Domain ◽  
Computational Difficulty ◽  
Deepwater Risers

A floating production system is exposed to many different environmental conditions over its service life. Consequently, the long-term fatigue analysis of deepwater risers is computationally demanding due to the need to evaluate the fatigue damage from a multitude of sea states. Because of the nonlinearities in the system, the dynamic analysis is often performed in the time domain. This further compounds the computational difficulty owing to the time consuming nature of time domain analysis, as well as the need to simulate a sufficient duration for each sea state to minimize sampling variability. This paper presents a new and efficient simulation technique for long-term fatigue analysis. The results based on this new technique are compared against those obtained from the direct simulation of numerous sea states.

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.

Case Study From Singapore

2020 ◽  
pp. 195-200
Keyword(s):  
Health Care ◽  
Disease Prevention ◽  
Gold Standard ◽  
Business Leaders ◽  
Review Panel ◽  
World Class ◽  
High Level ◽  
Global And Local

In the decades since Singapore’s independence in 1965, the nation has transformed from one facing basic challenges related to sanitation and disease prevention, to a world-class economy and a gold standard for health care. Factors that contribute to this trajectory include a stable government with a long-term vision of how Singapore should grow economically, guided by a high-level Economic Review Panel of global and local business leaders, international and local academics, and political officeholders. This group meets periodically ...

Application of Direct Hydrodynamic Loads in Spectral Fatigue Analysis

2017 ◽  
Author(s):  
Yogendra Parihar ◽  
Saikat Dan ◽  
Karan Doshi ◽  
Shivaji Ganesan Thirunaavukarasu
Keyword(s):  
Transfer Function ◽  
Stress Transfer ◽  
Bending Moment ◽  
Direct Calculation ◽  
Fatigue Analysis ◽  
Direct Application ◽  
Fe Model ◽  
Bending Moments ◽  
Hydrodynamic Loads ◽  
Fatigue Assessment

It is common practice to employ direct calculation procedures for spectral based fatigue assessment. Numerical codes are used to compute direct hydrodynamic loads. There are several complexities and nuances associated with application of loads on finite element (FE) model. It is a computationally expensive task especially when a large number of cases need to be analyzed (for e.g. spectral fatigue analysis). The present paper outlines an approach to evaluate the stress transfer function based on the direct application of moments (vertical bending, horizontal bending and torsional moments) computed using a frequency-domain based sea-keeping code. Multi-point constraint (MPC) method is utilized for application of bending moment. The structural responses computed using direct application of the bending moments (Method 1) and the panel pressures (Method 2) are compared. The evaluated stress transfer function is used for spectral fatigue analysis. Overall, the present study provides a methodology for spectral fatigue assessment using direct application of bending moments.

A Frequency Domain Approach for Random Fatigue Analysis of Steel Catenary Risers at Brazil’s Deep Waters

2004 ◽  
Author(s):  
Claudio Marcio Silva Dantas ◽  
Marcos Queija de Siqueira ◽  
Gilberto Bruno Ellwanger ◽  
Ana Lu´cia F. Lima Torres ◽  
Marcio Martins Mourelle
Keyword(s):  
Frequency Domain ◽  
Fatigue Damage ◽  
Time Domain ◽  
Oil And Gas ◽  
Large Diameter ◽  
Water Injection ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Fatigue Analysis ◽  
Steel Catenary Riser

The steel catenary riser was adopted by Petrobras as a cost-effective alternative for oil and gas export and for water injection lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. The installation of the P-18 SCR was a pioneer project of a free-hanging steel catenary riser linked to a semi-submersible [1] and demonstrated the technical feasibility of the concept. Fatigue damage verification is an important issue in SCR design, demanding a high number of loading cases to be analyzed. The random time domain nonlinear analysis is considered an attractive and reliable tool for fatigue analysis as nonlinearities are properly modeled and the random behaviour of environmental loadings is considered. As time domain analysis is high computer time consuming, the frequency domain analysis has been considered as an alternative tool for the initial phases of riser design to be used mainly for fatigue damage verification. This paper presents a methodology developed to perform a linearized frequency domain analysis aiming at fatigue damage verification. Two drilling risers were analyzed with the frequency domain procedure developed. The model of a steel lazy-wave riser was analyzed both in frequency and time domain in order to compare fatigue damage results. The analyses were performed using the Petrobras’s in-house computer codes ANFLEX, ALFREQ and POSFAL developed and implemented as part of projects from CENPES/PETROBRAS with “COPPE/UFRJ -The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”.

A Theoretical Method to Estimate the Fatigue Life of Tensile Armors of Flexible Pipes

2018 ◽  
Author(s):  
Kaien Jiang ◽  
Yutian Lu ◽  
Yong Bai
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Theoretical Method ◽  
Mean Stress ◽  
Flexible Pipe ◽  
Friction Coefficients ◽  
Flexible Pipes ◽  
Damage Theory ◽  
Rainflow Counting

This paper mainly focuses on a theoretical methodology to calculate the fatigue life of tensile armor of flexible pipes. This approach employs the local model of flexible pipe that converts forces and moments obtained in time-domain global analyses into stresses in the spiral tendons of tensile armor layer. The stresses are then processed by rainflow counting methods, and S-N curves are adopted to evaluate the fatigue damage of tensile armors. Finally, Miner linear cumulative damage theory is used in order to calculate the accumulated fatigue damage. A case study on the fatigue life of a flexible pipe employing this methodology is presented, and the fatigue life of flexible pipe is obtained. The main points addressed in the study are the effect of mean stress and friction coefficients. The results indicate that the inner tensile armor at suspension point is the most prone to fatigue damage, in addition, mean stress correction and friction coefficients strongly influence the fatigue life of flexible pipes.

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 Hang-Off Model to Evaluate Fatigue Damage at Riser Hang-Off

2013 ◽  
Author(s):  
Yucheng Hou ◽  
Jiabei Yuan ◽  
Yanqiu Zhang ◽  
Zhimin Tan ◽  
Terry Sheldrake
Keyword(s):  
Dynamic Simulation ◽  
Fatigue Damage ◽  
Time Domain ◽  
Damage Assessment ◽  
Global Analysis ◽  
Time History ◽  
Fatigue Analysis ◽  
Analysis Software ◽  
External Function ◽  
The Time Domain

Fatigue damage assessment at the flexible riser hang-off location, where the pipe frequently endures maximum tension and curvature variations, is key to verify design integrity for service life. Traditionally, the fatigue analysis is performed in a separate local structure model, as the commercial global analysis software lacks the capability of handling the local behavior of the riser structural component, which is dependent on materials and manufacturing processes. During global fatigue analysis, the riser configuration is built with pinned connected at the hang-off point. The resulting tension and angle responses at the hang-off location, are then input to a local model to perform the stress and fatigue analysis, where the detailed pipe layer structure and bend stiffener are modeled. This traditional approach is conservative, time costly and is often limited to regular wave approach. Wellstream developed an external function to work with specialized commercial riser dynamic analysis software. The external function simulates the detailed behaviour of flexible pipe structure components and the resulting bending hysteresis during dynamic simulation in the time domain. Therefore, the stress time history of the tensile armour becomes available at the end of global simulation in the time domain and is ready for fatigue damage assessment by rain flow counting. This paper presents a study case where the fatigue assessment is performed directly at the hang-off region within the riser global dynamic simulation. The riser hang-off is situated at the top of the I-tube and a bend stiffener is fixed at the bottom of the I-tube. I-tube and pipe section are precisely modeled as pipe-in-pipe facility, where the interaction of riser/I-tube can be captured.

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