A Comparison of Two Wave Models and Their Influence on Fatigue Damage in Ship Structures

2013 ◽  
Author(s):  
Wengang Mao ◽  
Fredhi Agung Prasetyo ◽  
Jonas W. Ringsberg ◽  
Naoki Osawa
Keyword(s):  
Fatigue Damage ◽  
Failure Modes ◽  
Maritime Industry ◽  
Ship Structures ◽  
Fatigue Assessment ◽  
Practical Applications ◽  
The North ◽  
Fatigue Design ◽  
Wave Models ◽  
Different Sources

In the maritime industry, fatigue failure is one of the most significant failure modes for ship structures. The fatigue damage in ship structures is mainly caused by the variation of wave loadings applied on ships, leading to variable structural stresses. Therefore, a reliable description of wave environments encountered during a ship’s service life is essential for accurate fatigue assessment of ship structures. Besides the wave scatter diagram provided by classification society rules, different statistical wave models have also been built up to model wave environments along arbitrary ship routes. The wave models could provide more specific wave environment for any chosen sailing routes of an individual ship. They may have the potential to be used for some practical applications, such as conceptual ship fatigue design, remaining fatigue life prediction when a ship plans to change its original trade region, and crack maintenance planning etc. Since the development of these models may be based on different sources, e.g. satellite measurements, hindcast data, buoys, etc., the reliability and consistence of wave generations from various wave models must be validated by the measured wave environments in order to be used for those practical applications. In this paper, waves generated from two different wave models, one based on hindcast data and one mainly on satellite data, are compared with measured wave environments encountered by a 2800 TEU container vessel on the North Atlantic route. These wave models are used in the calculation of the fatigue damage in the vessel. The results obtained using waves generated from the two wave models are compared with the fatigue damage calculated based on strain measurements in the ship. Recommendations for future development of the wave models and further investigation to make the applications more realistic for ship fatigue assessment are also presented.

The Effect of Whipping/Springing on Fatigue Damage and Extreme Response of Ship Structures

2010 ◽  
Author(s):  
Wengang Mao ◽  
Jonas W. Ringsberg ◽  
Igor Rychlik
Keyword(s):  
Fatigue Damage ◽  
North Atlantic Ocean ◽  
Gaussian Model ◽  
Container Ship ◽  
Level Crossing ◽  
Ship Structures ◽  
High Frequency Response ◽  
The North ◽  
Extreme Response ◽  
Wave Induced

Wave-induced vibrations, also known as whipping and springing, are defined as the high frequency response of ship structures. In this paper, the fatigue damage caused by whipping and springing is presented by investigating the amidships section of a 2800 TEU container ship that operates in the North Atlantic Ocean. A simplified fatigue model, originally from the generalized narrow-band approximation for Gaussian load, is employed to include the damage contribution from wave-induced vibrations. In this model, the significant response range hs and the mean stress up-crossing frequency fz are simplified using only the wave-induced loading and encountered wave frequency, respectively. The capacity and accuracy of the model is illustrated by application on the measurements of the 2800 TEU container ship for different voyages during 2008. The whipping-induced contribution to the extreme response is investigated by means of the level crossing approach. It shows that the level crossing model for Gaussian load cannot be used for the prediction of extreme responses, such as the 100-year stress, based on a half-year full-scale measurement. It is found that a more complicated non-Gaussian model is required to consider the contribution from whipping.

Fatigue Strength Assessment of Ship Structures Based on the Crack Propagation Theory

2009 ◽  
Author(s):  
Song Niu ◽  
Guoqing Feng ◽  
Huilong Ren ◽  
Jian Zhang
Keyword(s):  
Crack Propagation ◽  
Function Method ◽  
Failure Modes ◽  
Analysis Method ◽  
Propagation Theory ◽  
Ship Structures ◽  
Element Analysis ◽  
Fatigue Assessment ◽  
Strength Assessment ◽  
Simplified Procedures

Fatigue damage is one of the main failure modes of ship structures. At present, the fatigue assessment of ship structures is mainly based on S-N method, such as the simplified procedures by classification societies or the spectral fatigue analysis method, etc. Because the initial flaw or crack can not be taken into account in S-N method, the fatigue assessment of ship structures based on fracture mechanics or crack propagation theory is worth to be studied. In this paper, the crack propagation theory based fatigue assessment of ship structures is studied. First, the calculation of stress intensity factor based on finite element analysis and weight function method are given, then Paris model is used to predict the crack propagation life. Finally, a numerical example is given to show the procedure of fatigue assessment of ship structures.

Fatigue Variation in Ships due to the Variability of Environmental Loads

2012 ◽  
Author(s):  
Wengang Mao ◽  
Zhiyuan Li ◽  
Jonas W. Ringsberg ◽  
Igor Rychlik
Keyword(s):  
Fatigue Damage ◽  
Structural Integrity ◽  
Structural Strength ◽  
Fatigue Cracks ◽  
Maritime Industry ◽  
Fatigue Design ◽  
Routing Design ◽  
Potential Use

The design and analysis of structural strength against fatigue failure always includes large uncertainties. It is crucial to understand and identify the most important uncertainties that affect the performance, functionality and service life of an engineering structure — in particular when it comes to the safety aspect, which may involve the risk of loss of human lives. In maritime industry, it is known that due to various sources of uncertainties in ship fatigue design, some ships may survive (the occurrence of fatigue cracks which may endanger the structural integrity) much longer than their designed life, while other ships develop fatigue cracks far too early. The current investigation presents some of the most important uncertainties and their effects on the accuracy of fatigue assessments in a container vessel. The study emphasizes the analysis of the fatigue damage variation when the ship is sailing on different routings between two ports. A fatigue model developed by the authors for ship fatigue routing application is employed to estimate the long term fatigue damage. In this model, only a few parameters, i.e. the encountered significant wave height and operational profiles, are needed. The procedure of using this model for a ship fatigue routing design is described in detail. Its potential use and benefits are demonstrated in a case study by a 2,800 TEU container ship using both full-scale measurements and hindcast wave data. It is shown that awareness and careful fatigue routing design can reduce fatigue damage significantly by up to 50%!

Validation of Spectral Fatigue Assessment of a West-Africa FPSO Using Full-Scale Measurements

2021 ◽  
Author(s):  
Alexandru Andoniu ◽  
Jérôme de Lauzon ◽  
Remco Hageman ◽  
Pieter Aalberts ◽  
Didier L'Hostis ◽  
...  
Keyword(s):  
West Africa ◽  
Fatigue Damage ◽  
Wave Energy ◽  
Fatigue Analysis ◽  
Full Scale ◽  
Fatigue Assessment ◽  
Sources Of Uncertainty ◽  
Wave Conditions ◽  
Offshore Industry ◽  
Different Sources

Abstract In order to ensure structural integrity and safe operations, fatigue assessment of structural details is a key aspect of design and verification procedures for FPSOs. Spectral fatigue analysis is widely used in the offshore industry to assess damage induced by wave loading. However, the actual fatigue accumulation endured by units in operations usually differs from predictions due to the assumptions made at the design stage. One of the sources of uncertainty is the representation of the encountered sea states. The objective of this paper is to use in-situ measurements as a reference for evaluating the accuracy of spectral fatigue analysis and to investigate the influence of wave energy description on the fatigue assessment. Structural health monitoring systems have been increasingly used in the last decade in the offshore industry as they constitute a valuable source of information regarding the actual operating conditions, structural response, or encountered environmental conditions. This data can be used to update fatigue assessment in order to determine the remaining service life, understand how the structure is aging, or support for decision making regarding inspections, maintenance, or lifetime extension. The work presented is based on such information gathered during a measurement campaign performed on a spread-moored FPSO in West Africa. Measured strain time histories at several locations on the hull have been used to derive the actual fatigue damage endured by the unit. These damages are compared to the ones determined from spectral fatigue analysis using stress transfer functions obtained from frequency domain hydro-structure computations. Multiple analyses have been performed to evaluate the impact of different sources of statistical wave data and wave energy descriptions on the fatigue assessment. The wave conditions used originate from wave buoy measurements and hindcast data. Overall, the good agreement between full-scale measurements and calculations confirms the suitability of spectral methods for determining fatigue damage. When incomplete information is available, which is often true in the case of wave statistics, assumptions have to be made regarding parameters such as spectrum shape or wave spreading. However, using the full description of wave energy spectra, if available, can be a way of reducing uncertainties and removing unnecessary assumptions in such analysis. The results of this work show how fatigue assessment can be improved by gaining insight into the different sources of uncertainty, notably the sea state representation. With increasing focus on digital solutions, these results show realistic potential for virtual hull monitoring solutions based on accurate numerical models and realistic representation of wave conditions.

Background for New Revision of DNV-RP-C203 Fatigue Design of Offshore Steel Structures

2010 ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Steel Structures ◽  
Electronic Version ◽  
Fatigue Assessment ◽  
Fatigue Design ◽  
Different Types ◽  
Background Material ◽  
Made In

The DNV-RP-C203 Fatigue Design of Offshore Steel Structures is being used by a number of different companies for fatigue assessment of different types of structures. This has resulted in questions to DNV about background for the different sections in the document. It is therefore important that the basis for this document is open to the industry. Quite a lot of the background material has also been published earlier at conferences and in journals. In some situations it has been found that the content can be improved to better suite the industry. The document is presented in an electronic version making revisions easy. Therefore it has been revised several times since the last official presentation of a revision in 2005. The present paper gives an overview of the most significant changes made in the document since the 2005 revision. Some of these changes are already included in the present version of DNV-RP-C203. The remaining changes will be included in a revision dated 2010.

Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice

2021 ◽  
Author(s):  
Chana Sinsabvarodom ◽  
Bernt J. Leira ◽  
Wei Chai ◽  
Arvid Naess
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Models ◽  
Full Scale ◽  
Mooring Line ◽  
Stress Range ◽  
Station Keeping ◽  
Probability Models ◽  
Line System ◽  
Fatigue Assessment ◽  
Rainflow Counting

Abstract The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking was employed in order to represent a supply vessel equipped with a mooring line system, and the realtime loading during the full-scale measurement was recorded. The second vessel Tor Viking was serving as an ice breaker in order to maintain the physical ice management activities with different ice-breaking schemes, i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns were investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Fatigue assessment based both on Rainflow counting and fitted probabilistic models were performed. For the latter, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress ranges represented by application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the Rainflow counting approach. Among the different scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.

Concrete Fatigue Life Characteristics of the Different Survival Rates in the Lateral Pressure Conditions

2012 ◽  
Vol 600 ◽  
pp. 250-255
Author(s):  
Qiang Cai ◽  
Ji Ming Kong ◽  
Ze Fu Chen
Keyword(s):  
Fatigue Life ◽  
Life Stress ◽  
Failure Modes ◽  
Survival Curve ◽  
Survival Rates ◽  
Life Distribution ◽  
Fatigue Design ◽  
Set Up ◽  
Fatigue Equation ◽  
Two Parameter

Under cyclic loading of concrete structures, fatigue failure is the main failure modes of fatigue, which has become the fatigue design of concrete structure must be considered, then the concrete fatigue studies must clarify the fatigue life of concrete under different survival curve S-N curve. Based on the statistics of the two parameter Weibull distribution theory, obtain the concrete under different survival rates of fatigue life distribution, namely to improve survival, reduce the fatigue life; stress level is reduced, the fatigue life is increased; and has set up more than 50% under different survival rates of concrete fatigue equation.

Fatigue Assessment of Concrete Members Strengthened by FRP Materials

2014 ◽  
Vol 617 ◽  
pp. 221-224 ◽  
Author(s):  
Alena Čavojcová ◽  
Martin Moravcik
Keyword(s):  
Fatigue Damage ◽  
Cross Section ◽  
Theoretical Approach ◽  
Material Properties ◽  
Beam Cross Section ◽  
European Standard ◽  
Fatigue Assessment ◽  
Concrete Members ◽  
Damage Structure ◽  
T Beam

Fatigue and fatigue damage leads to a change in material properties that can lead to the element failures. Generally, it is necessary to verify the influence of the fatigue effects on the concrete members according to European standard EC2, [1]. FRP materials have been possibly used for the fatigue damage structure rehabilitation. There we can apply the condition of the limit boundaries stress on concrete and limit force in FRP material theoretical approach. Fatigue assessment will be analyzed for T-beam cross section with reinforcement and strengthened FPR material in this paper.

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