Assessment of Wave-induced Fatigue Damage to Marine Pipelines in Intermediate Seas

2016 ◽  
Vol 26 (4) ◽  
pp. 385-391 ◽  
Author(s):  
Abbas Yeganeh-Bakhtiary ◽  
Naser Shabakhty ◽  
Ali Valipour ◽  
Hamzeh Gol-Zaroudi
Keyword(s):  
Fatigue Damage ◽  
Wave Induced

First Ocean Going Ships With Springing and Whipping Included in the Ship Design

2011 ◽  
Author(s):  
Gaute Storhaug ◽  
Erlend Moe ◽  
Ricardo Barreto Portella ◽  
Tomazo Garzia Neto ◽  
Nelson Luiz Coelho Alves ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Current Model ◽  
Life Time ◽  
Model Tests ◽  
Full Scale ◽  
Development Projects ◽  
Transient Vibration ◽  
Hull Girder ◽  
Fatigue Evaluation ◽  
Wave Induced

It is well known that ships vibrate due to waves. The wave induced vibrations of the hull girder are referred to as springing (resonance) and whipping (transient vibration from impacts). These vibrations contribute to the fatigue damage of fatigue sensitive details. An Ore Carrier of 400 000 dwt is currently being built by DSME, and at time of delivery, it will be the world’s largest bulk (ore) carrier. The scantlings of large ships must be carefully designed with respect to global loading, and when extending the design beyond experience, it is also wise to consider all aspects that may affect operation and the life time costs. The vessel will also enter a long term contract and is therefore to be evaluated for 30 year Brazil-China operation. In order to minimize the risk of fatigue damage, the vessel is designed according to DNV’s class notation CSA-2 requiring direct calculations of the loading and strength. Further it has been requested to include the effect of springing and whipping in the design. Reliable numerical tools for assessing the additional fatigue effect of vibrations are non-existing. DNV has, however, developed an empirical guidance on how the additional effect may be taken into account based on previous development projects related to the effect of vibrations on large ore carriers Due to the size and route of operation of the new design, it has, however, been required by the owner to carry out model tests in both ballast and cargo condition in order to quantify the contribution from vibration. The results from this project have been used for verification and further calibration of DNV’s existing empirical guidance. A test program has been designed for the purpose of evaluating the consequence in head seas for the Brazil to China trade. Full scale measurements from previous development projects of ore carriers and model tests have been utilized to convert the current model tests results into estimated full scale results for the 400 000 dwt vessels. It is further important to carefully consider how the vibrations are to be included in the design verification, and to develop a procedure for taking into account the vibrations which results in reasonable scantlings based on in-service experience with similar designs and trades. This procedure has been developed, and a structural verification has been carried out for the design. The final outcome of the model test was in line with previous experience and in overall agreement with DNV’s empirical guidance, showing a significant contribution from vibrations to the fatigue damage. The springing/whipping vibrations more than doubled the fatigue damage compared to fatigue evaluation of the isolated wave induced loading. The cargo condition vibrated relatively more than experienced on smaller vessels. Various sources to establish the wave conditions for the Brazil to China ore trade were used, and the different sources resulted in significant differences in the predicted fatigue life of the design.

The Effect of Bow Shape on the Springing/Whipping Response of a Large Ocean-Going Vessel: Investigated by an Experimental Method

2007 ◽  
Author(s):  
Gaute Storhaug ◽  
Torgeir Moan
Keyword(s):  
Fatigue Damage ◽  
Transfer Functions ◽  
Vertical Vibration ◽  
Full Scale ◽  
Relative Importance ◽  
High Frequency Response ◽  
Bow Flare ◽  
Excitation Mechanisms ◽  
The Difference ◽  
Wave Induced

Wave induced vibrations often referred to as springing and/or whipping increase the fatigue and extreme loading in ship hull girders. Both effects are disregarded in current ship rules. Various numerical codes exist for predicting the wave induced vibrations, but so far they are not considered reliable. Another means to investigate the importance of the high frequency response, although more resource demanding, is to carry out full scale measurements and/or model tests. Recently, full scale measurements of blunt ships have been carried out by DNV, and in this paper one of these ships was considered and tested in a towing tank to evaluate the additional fatigue damage due to the wave induced vibrations. Different excitation sources may excite the 2-node vertical vibration mode depending on ship design, and it is not straight forward to determine which is more important. The relative importance of the excitation mechanisms are investigated by two approaches in this paper. The first approach separates the whipping from springing to illustrate their relative importance based on basic theory in combination with model test results. The linear and second order transfer functions are utilized in this procedure. The second approach deals with the effect of the bow design on the additional fatigue damage. Three different bows were tested. The first bow design is identical to the real ship. The second bow design is a simplified version of the first one, by removing the bulb and flare. The third bow is fundamentally different from the two former blunt bows. Bow three is sharp pointed with a vertical sharp stem and vertical ship sides. The results indicate that the importance of whipping depends on the sea state, but that it is of similar importance as springing for the sea states that contributes most to the fatigue damage. Moreover, the difference in the additional fatigue damage due to wave induced vibrations for different bow shapes is moderate. This indicates that vessels with pointed bows and without pronounced bow flare, such as LNG vessels, may have a similar contribution from wave induced vibrations. Modern container vessels, which are more slender, but with pronounced bow flares should be further investigated.

Effect of Wave Induced Loading and Line Loading in Fully Stochastic Fatigue Assessment for West Africa FPSO

2004 ◽  
Author(s):  
T. H. Park ◽  
J. H. Lee ◽  
J. W. Cho ◽  
H. S. Shin
Keyword(s):  
West Africa ◽  
Fatigue Damage ◽  
Bending Moment ◽  
Ship Motions ◽  
Piping System ◽  
Site Specific ◽  
Fatigue Assessment ◽  
Loading Effects ◽  
Wave Induced ◽  
Side Shell

The fatigue assessment for a caisson of the interface between a caisson and a FPSO hull has been performed based on the FMS (Fatigue Methodology Specification) [1]. Investigation is focused on the various loading effects including inertia loading due to ship motions from a site specific swell, sea and line loading from the submerged caisson connected to the side shell of FPSO. The fully stochastic method was used for estimating damage levels from wave loadings. The component-based method was used for line loading effects. The two kinds of results from each case were combined the variance and mean period combination. For the inertia loading, it is shown that a hull deforming due to vertical bending moment is the principal effect for a fatigue assessment. For the line loading, it is found that the loading effect due to the submerged piping system connected to the side shell of FPSO is not significant for the fatigue of the side shell supporting structure. In conclusion, the fatigue damage from the site-specific swell is dominant effect among overall fatigue damage components of FPSO in the specific site condition of West Africa.

Fatigue Design and Analysis of Offshore Pipelines and Risers Subjected to Waves and Currents

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Fatigue Damage ◽  
Damage Accumulation ◽  
Coupling Effect ◽  
Limit State ◽  
Ultimate Limit State ◽  
Offshore Pipelines ◽  
Fatigue Design ◽  
Fatigue Damage Accumulation ◽  
Waves And Currents ◽  
Wave Induced

The industry consensus would appear that the effect of currents on wave-induced fatigue damage accumulation is assumed as insignificant and can be ignored. Only when dealing with stability, ultimate limit state design, and vortex-induced vibration (VIV), is the recommended industry practice to consider both currents and waves simultaneously, except for fatigue design. This paper presents a study on how environmental loads should be considered in terms of currents and waves for the fatigue life design of offshore pipelines and risers. The study is intended as a spur to redress the misapprehension by focusing on the coupling effect of direct waves and currents in the context of fatigue damage assessment. It is demonstrated unequivocally that waves and currents cannot be decoupled for fatigue design assessments. Wave-induced fatigue with the inclusion of currents is manifested twofold, not only the increased mean stress correction effect but also higher total damage accumulation due to elevated stress ranges. The practice of using wave histograms while ignoring currents is shown to result in an unacceptable nonconservative fatigue design. Both effects should be accounted for in the engineering assessment. A first-order correction factor involving the ratio of current and wave velocities is introduced to evaluating the environmental load coupling effect. It is recognized that fatigue associated specifically with VIV phenomena is well understood and documented elsewhere, its discussion is thus out with the aims of this paper.

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 Damage Estimation of Stinger Main Hinges Subject to Wave Loadings

2010 ◽  
Author(s):  
Xiangfeng Zhang ◽  
Wenshou Zhang ◽  
Qianjin Yue ◽  
Xin Li
Keyword(s):  
Structural Health Monitoring ◽  
Fatigue Damage ◽  
Health Monitoring ◽  
Hot Spots ◽  
Damage Mechanics ◽  
Measurement Data ◽  
Assessment Method ◽  
Water Tank ◽  
Structural Health ◽  
Wave Induced

The laying of subsea pipelines is usually carried out by means of S-lay technology. As stingers become longer and longer, wave-induced fatigue damage problem for the stinger main hinges connecting both the stinger and the stinger adjustment frame fore leg to the vessel stern via a common shaft may have to be taken into consideration. Usually, there is a structural health monitoring system (SHMS) to be installed on the stinger for performance assessment. A procedure for assessing long-term wave-induced fatigue damage to a stinger is thus presented in this paper with continuum damage mechanics (CDM)-based fatigue damage assessment method. By taking the stinger of DPV7500 being built for Chinese Offshore Oil Engineering Corporation (COOEC) as an example, a structural health monitoring-oriented finite element model of the stinger is established. Water tank experiments were conducted to measure the roll, pitch and heave motion responses of the vessel model for different wave height, wave period and directions. The measurement data are then used to carry out the stress analyzes of the stinger to identify stress characteristics at hot spots of the stinger. The accumulative fatigue damage at hot spots during the stinger design life is finally evaluated using a CDM-based fatigue damage evolution model.

The Consequence Method: An Approach for Estimating Roll Damping in Transportation Fatigue Analyses

2017 ◽  
Author(s):  
Tormod Bøe ◽  
Limin Yang ◽  
Erik Falkenberg
Keyword(s):  
Fatigue Damage ◽  
Viscous Damping ◽  
Scatter Diagram ◽  
Roll Damping ◽  
Time Of Year ◽  
Correct Estimation ◽  
Wave Induced ◽  
Partial Damage ◽  
Transportation Route

In order to compute fatigue damage during offshore transports it is necessary to assume a description of the sea states encountered during the voyage. In recent years, it has become a common approach to apply directional long-term scatter diagrams for the transportation route, taking into account vessel speed, course and time of year for the departure. An important contribution to the transportation fatigue damage is usually the wave induced inertia load. For ship shaped vessels additional viscous damping needs to be included in order to estimate correct roll response. However, since viscous roll damping is non-linear, correct estimation of fatigue damage can only be obtained by computing partial damage for all individual sea states in the scatter diagram. This becomes very time-consuming and is usually not done. Instead, the roll damping level is tuned to match typical mean sea states in the scatter diagram. The roll damping will then be too low for higher sea states and too large for smaller sea states. When choosing the roll damping level, the aim should be to obtain an overall error in transportation fatigue damage which is minimized. This paper describes a method to estimate a representative viscous roll damping level for transportation fatigue analyses.

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