Long-Term Fatigue Damage of Ship Structures Under Nonlinear Wave Loads

2002 ◽  
Vol 39 (02) ◽  
pp. 95-104
Author(s):  
Xue KangGu ◽  
Torgeir Moan
Keyword(s):  
Fatigue Damage ◽  
Nonlinear Wave ◽  
Direct Analysis ◽  
Linear Wave ◽  
Wave Loads ◽  
Ship Structures ◽  
Hull Girder ◽  
Structural Fatigue ◽  
Large Container

Fatigue is a principal mode of failure in ship structures, especially when high tensile steels are applied. Although significant efforts have been made to predict fatigue damage, there are still uncertainties existing, e.g., in the stress histories that cause fatigue. This paper addresses estimation of fatigue damage in ships under wave loads, with an emphasis on containerships, which have large bow flare and low hull girder rigidity. Linear and nonlinear wave-induced loads as well as dynamic effects due to hull flexibility, i.e., whipping, are researched. With the direct analysis method of fatigue, the nature of the wave loading, hull rigidity, structural damping, stress range counting algorithm and SN curve on structural fatigue damage are investigated. In long-term fatigue damage estimates, the influence of different sea environments is numerically analyzed. The importance of nonlinearity of wave loads and especially the whipping on the structural fatigue damage is demonstrated by calculation for a large container vessel with large flare and lowest natural frequency of 0.749 Hz. Depending upon sea environments and SN curves used in long-term predictions, the fatigue damage based on nonlinear wave loads (excluding whipping) is 10–100% larger than that due to linear wave loads; the fatigue damage based on nonlinear combined loads (including whipping) may be 1–9 times larger than that of steady-state nonlinear wave loads.

Research on Ship Structural Fatigue Damage Under Nonlinear Wave Bending Moment

2017 ◽  
Author(s):  
Jingxia Yue ◽  
Lihua Peng ◽  
Wengang Mao ◽  
Chi Zhang ◽  
Wei Dong ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Frequency Response ◽  
Fatigue Damage ◽  
Nonlinear Wave ◽  
Model Test ◽  
Bending Moment ◽  
Irregular Waves ◽  
Wave Loading ◽  
Ship Structures ◽  
Structural Fatigue

Loads acting on ship structures are complex and randomly over time and the nonlinear effect caused by wave loading is one of the research focus. The linear and nonlinear vertical wave bending moment (VBM) in different speeds and sea states and their effects on ship structural fatigue strength were investigated for a flat container with high ratio of width to depth. The VBM under the linear regular waves and irregular waves were calculated based on the three dimension (3D) potential theory. The considered nonlinear wave loading was caused by sea pressure near the mean free surface as well as the geometric nonlinearity. Hydrodynamic calculations in regular wave were presented to figure out the frequency response function (FRF) of VBM in the mid-ship section. Irregular waves were verified to obtain the VBM history in 4 sea states. What’s more, VBMs from a segmented elastic model test were obtained to investigate the influence of nonlinearity. On the basis of the wave loadings obtained from simulation and test, the hotspot stress histories under irregular waves were deduced in time domain by using the beam theory. Fatigue cumulative damage per hour under several random sea states were obtained on the basis of the rain-flow counting and S-N curve. Based on the fatigue damage from the numerical analysis and model test, it is believed that speeds and significant wave height have a positive correlation with the fatigue damage of ship structures. A good agreement was obtained between the numerical analysis values and the low frequency part of the test and the nonlinear analysis in the simulation could offer reasonable prediction for the fatigue damage caused by the wave frequency response. Also shown as the test result, fully nonlinearities have a great contribution to the fatigue damage.

Full-Scale Measurements on Hull Response of a Large-Container Ship in Service

2006 ◽  
Author(s):  
Kenichiro Miyahara ◽  
Ryuju Miyake ◽  
Norikazu Abe ◽  
Atsushi Kumano ◽  
Masanobu Toyoda ◽  
...  
Keyword(s):  
High Harmonic ◽  
Bending Moment ◽  
Full Scale ◽  
Linear Wave ◽  
Container Ship ◽  
Wave Loads ◽  
Non Linear ◽  
Large Container ◽  
Probability Density Distributions

In order to investigate hull responses of post-Panamax container ships in the actual sea, full-scale measurements on hull responses of a post-Panamax container ship in service were conducted. In linear wave domain, the probability density distributions of hull responses obtained by full-scale measurements were compared with the Rayleigh distributions to check on the range of the applicability, and comparisons with the long-term distributions of the longitudinal stress obtained by full-scale measurements and the direct structural analyses based on the wave loads analyzed by using the linear 3D Rankine source method were made to verify the accuracy. In non-linear wave domain, the measured longitudinal stresses showed the asymmetry of vertical bending moment. The long-term distributions of hull responses, which have the high harmonic components, obtained by full-scale measurements were compared with the numerical results analyzed by using non-linear methods to investigate the non-linearity on hull responses of container ship.

Time Domain Analysis of Springing and Whipping Responses Acting on a Large Container Ship

2011 ◽  
Author(s):  
Yongwon Lee ◽  
Zhenhong Wang ◽  
Nigel White ◽  
Spyros E. Hirdaris
Keyword(s):  
Time Domain ◽  
Nonlinear Effects ◽  
Time Domain Analysis ◽  
Container Ship ◽  
Wave Loads ◽  
Ocean Engineering ◽  
Hull Girder ◽  
Engineering Research ◽  
Large Container ◽  
Element Method

As part of WILS II (Wave Induced Loads on Ships) Joint Industry Project organised by MOERI (Maritime and Ocean Engineering Research Institute, Korea), Lloyd’s Register has undertaken time domain springing and whipping analyses for a 10,000 TEU class container ship using computational tools developed in the Co-operative Research Ships (CRS) JIP [1]. For idealising the ship and handling the flexible modes of the structure, a boundary element method and a finite element method are employed for coupling fluid and structure domain problems respectively. The hydrodynamic module takes into account nonlinear effects of Froude-Krylov and restoring forces. This Fluid Structure Interaction (FSI) model is also coupled with slamming loads to predict wave loads due to whipping effects. Vibration modes and natural frequencies of the ship hull girder are calculated by idealising the ship structure as a Timoshenko beam. The results from springing and whipping analyses are compared with the results from linear and nonlinear time domain calculations for the rigid body. The results from the computational analyses in regular waves have been correlated with those from model tests undertaken by MOERI. Further the global effects of springing and whipping acting on large container ships are summarised and discussed.

Analysis of the Fatigue Damage on the Offshore Wind Turbines Exposed to Wind and Wave Loads Within the Typhoon Area

2004 ◽  
Author(s):  
Atsushi Yamashita ◽  
Kinji Sekita
Keyword(s):  
Fatigue Damage ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Wave Load ◽  
Offshore Wind Turbines ◽  
Simple Addition ◽  
Recorded Data ◽  
Term Data

For the design of offshore wind turbines exposed to wind and wave loads, the method of combining the wind load and the wave load is significantly important to properly calculate the maximum stresses and deflections of the towers and the foundations1). Similarly, for the analysis of the fatigue damage critical to the structural life, the influences of combined wind and wave loads have not been clearly verified. In this paper fatigue damage at the time of typhoon passing is analyzed using actually recorded data, though intrinsically long-term data more than 10years should be used to properly evaluate the fatigue damage. This paper concludes that the fatigue damage of the tower caused by the wave load is not substantial and, thus, the fatigue damage by the combined wind and wave load is only 2–3% larger than the simple addition of the independent fatigue damages by the wind and the wave loads. The fatigue damage of the tower top, which is required to reduce the diameter in order to minimize the aerodynamic confliction with blades, is larger than that of the tower bottom. The fatigue damage at the foundation by the combined wind and wave load is 25% larger than the simple addition of the wind and wave damages, as the foundation is directly exposed to the wave load. For the foundation, the proper structural section can be designed in order to improve the structural performance against fatigue.

The Effect on Large Container Ships’ Fatigue due to Springing Loads Coupling Horizontal and Torsional Vibrations

2018 ◽  
Author(s):  
Hui Li ◽  
Huifen Xu ◽  
Huilong Ren ◽  
Xiaoxi Shen ◽  
Yubo Wang
Keyword(s):  
Fatigue Damage ◽  
Torsional Vibration ◽  
Calculation Method ◽  
Wave Loads ◽  
Analysis Method ◽  
Element Analysis ◽  
Hull Structure ◽  
Torsional Loads ◽  
Large Container ◽  
Simplified Calculation

The issue of hydroelasticity caused by hull vibration has become an unavoidable problem in the design and verification of large ships. Driven by environmental protection and economical efficiency, the size of ships are increasingly larger, and the resulting springing and whipping response and their effects on fatigue damage has been paid more and more attention especially for ultra large container ships (ULCS). Many classification societies typically check fatigue damage caused by vertical bending when considering springing, while it needs to be emphasized that large container ships can suffer severe torsional loads compared to other large ships due to wide breath and big hatch openings. In the existing stress calculation method, the finite element analysis method obviously has a high calculation accuracy. However, there are so much work to do with FEM model established, and partially refined, operated at all sea states etc., which not only requires much time, but also higher computing equipment. Therefore, in this paper, a simplified calculation method of fatigue damage considering the effect of bending and torsion is proposed, and a 21000TEU will be calculated by this method. The wave loads on the hull structure will be estimated based on the 3D linear hydroelastic theory coupling horizontal and torsional vibration, and the stress caused by bending and torsion will be obtained respectively. Finally, the fatigue damage is calculated by spectral analysis method considering high frequency springing loads. Then the effect on large container ships’ fatigue due to bending and torsional vibration is discussed.

Fatigue Assessment for Ship Structure Acted on Non-Linear Wave Loads

2007 ◽  
Vol 353-358 ◽  
pp. 2786-2789
Author(s):  
Chao He Chen
Keyword(s):  
Fatigue Damage ◽  
Bending Moment ◽  
Linear Wave ◽  
Wave Loads ◽  
Ship Structure ◽  
Random Seas ◽  
Non Linear ◽  
Bow Flare ◽  
Short Term Prediction ◽  
The Given

Efficient methods are described here to predict the fatigue damage of ship structure due to nonlinear wave loads that are produced in random seas. Firstly the effects of the non-linear waveinduced bending moment on the fatigue damage of ship structure with very large bow flare are presented in short-term prediction by the method of spectrum analysis. Then, the fatigue damage is estimated and analyzed in the given environment of long-term.

Full Scale Measurement of a Large Container Carrier on the Far East - Europe Route

2008 ◽  
Author(s):  
H. C. Yu ◽  
J. W. Choi ◽  
G. I. Park ◽  
S. Y. Han ◽  
S. C. Tai ◽  
...  
Keyword(s):  
Far East ◽  
Structural Response ◽  
Full Scale ◽  
Ship Motions ◽  
First Year ◽  
East Europe ◽  
Hull Girder ◽  
The Far East ◽  
Large Container

There is limited long term service experience with the modern generation of large container carriers and hence there is great interest in improving our understanding of the performance of these vessels. In an effort to assess the actual structural service performance of a large container carrier, a comprehensive full-scale measurement system was developed to measure the wave environment, ship motions and structural response. The system was installed on an 8063 TEU container carrier built in 2006, and the first year measurement campaign has successfully been completed. This paper presents a summary of noteworthy observations during the first year’s voyage records which includes ship motion, wind and wave conditions, and hull girder strains and derived hull girder bending and torsional moments. The observed vibratory responses of the hull girder are also presented.

Measurements of Wave Induced Hull Girder Vibrations of an Ore Carrier in Different Trades

2006 ◽  
Author(s):  
Gaute Storhaug ◽  
Erlend Moe ◽  
Gabriel Holtsmark
Keyword(s):  
Natural Frequency ◽  
Fatigue Damage ◽  
North Atlantic ◽  
Wave Forces ◽  
Wave Loading ◽  
Hull Girder ◽  
Wave Radar ◽  
Wave Induced ◽  
Vibration Damage

Currently, the conventional wave loading is the only effect considered in fatigue assessment of ships. DNV has recently confirmed that fatigue damage from wave induced vibrations may be of similar magnitude as from the conventional wave loading (Moe et al. 2005). A 40% contribution to the total fatigue damage in deck amidships is documented through extensive measurements onboard an ore carrier (the reference ship) trading in the North Atlantic. The effect of strengthening the vessel, increasing the natural frequency by 10%, is ineffective to reduce the relative magnitude of the vibration damage. The wave induced vibration, often referred to as whipping and/or springing, does contribute to fatigue damage also for other ship types and trades (Moe et al. 2005). This paper considers the effect of trade. It indicates when the wave induced vibrations should be accounted for in the design phase with respect to fatigue damage. A second ore carrier (the target ship) is monitored with respect to the wave induced hull vibrations and their fatigue effect. Stress records from strain sensors located in the midship deck region are supplemented by wave radar and wind records. Based on the measurements, the vibration stress response and associated vibration induced fatigue damage are determined for varying wind- and wave forces and relative headings. While the reference ship operates in the Canada to Europe ore trade, the target ship trades between Canada and Europe, Brazil and Europe, and South Africa and Europe. A procedure is suggested by Moe et al. (2005) to estimate the long term fatigue damage for different trades by utilizing the measured data from the reference ship. The vibration and wave damage are considered separately. By comparing the measured wave environment and the DNV North Atlantic scatter diagram, the effect of routing indicated a reduction of the fatigue damage by one third. A slightly revised procedure is applied to estimate the effect of trade for the second ore carrier, comparing the long term predicted fatigue damage with the measured fatigue damage. The importance of trade is confirmed. However, the relative contribution of the vibration damage is shown to increase in less harsh environments. The target ship vibrates more than the reference ship for the same trade and Beaufort strength. The vibration damage of the target ship constitutes 56% of the total measured damage, and the high natural frequency is observed to have no significant effect.

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