Analysis on statistical uncertainties of wave loads and structural fatigue reliability for a semi-submersible platform

2021 ◽  
Vol 237 ◽  
pp. 109609
Author(s):  
Peng Yang ◽  
Jingru Li ◽  
Wei Zhang ◽  
Dongwei Wu ◽  
Xuekang Gu ◽  
...  
Keyword(s):  
Wave Loads ◽  
Fatigue Reliability ◽  
Structural Fatigue

Hull Deformation Effect on Membrane-Type LNG Containment Systems

2016 ◽  
Author(s):  
Bo Wang ◽  
Yung-Sup Shin ◽  
Eric Norris
Keyword(s):  
Structural Integrity ◽  
Water Pressure ◽  
Local Deformation ◽  
Fatigue Tests ◽  
Wave Loads ◽  
Insulation System ◽  
Structural Fatigue ◽  
Hull Structure ◽  
Membrane Type ◽  
Global Deformation

The objective of this study is to investigate the relationship between the maximum allowable hull deformation, which includes global elongation and local deflection, and the capacity of the CCS in membrane-type LNG vessels. The LNG CCS mainly consists of the primary barrier (e.g. a corrugated membrane for GTT MK III system and an invar membrane for GTT NO 96 system) and the insulation panel which is attached to the inner hull through mastics or couplers. The excessive hull elongation due to dynamic wave loads may cause fatigue damage of the primary barrier. Thus, the maximum allowable hull elongation (global deformation) can be determined based on the fatigue strength of the primary barrier. On the other hand, the excessive hull deflection due to cargo or ballast water pressure may cause failure of the insulation panel and the mastic. Therefore, the maximum allowable hull deflection (local deformation) in the hull design can be determined based on the strength of the insulation panel and the mastic. In the present paper, the determination of fatigue life vs. strain curves of materials has been summarized for the primary barrier. Fatigue curves based on either structural fatigue tests or standard specimen tests can be applied in fatigue assessment of a primary barrier. As an example, the finite element (FE) analysis has been conducted on the MK III CCS with the hull structure under pressure loads. Two different load cases including full load and ballast load conditions have been considered to evaluate the structural integrity of the insulation system in numerical simulations. FE results show that the mechanical behavior of the insulation system and the mastic under the maximum allowable hull deflection has been examined based on the yielding strength of each individual component. Finally, the complete procedure to determine the maximum allowable hull elongation and the maximum allowable hull deflection has been developed for meeting the requirements of containment system design for membrane-type LNG carriers.

Statistical Analysis of Loader’s Drive Axle Housing Random Load Spectrum

2011 ◽  
Vol 338 ◽  
pp. 456-459 ◽  
Author(s):  
Bu Zheng Wen ◽  
Jian Min Li ◽  
Zhong Tao Pei ◽  
Sheng Yu ◽  
Cuan Yang Sun ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Weibull Distribution ◽  
Fatigue Reliability ◽  
Load Spectrum ◽  
Distribution Fitting ◽  
Random Load ◽  
Structural Fatigue ◽  
History Of ◽  
Drive Axle ◽  
Drive Axle Housing

Statistical analysis of load spectrum is an important part on structural fatigue life and reliability research, it is generally considered that axle’s load spectrum follows Weibull distribution. This paper tested ZL50 loader’s loading history of different working conditions , and obtained the corresponding load spectrum by rain-flow counting method, then analyzed three distributions’ (normal distribution, lognormal distribution, Weibull distribution) fitting degree of load spectrum and effect on the fatigue reliability. Results show that the highest fitting degree of distribution function should be used to fit load spectrum, which can reduce the error in structural fatigue reliability prediction.

Automation of Structural Fatigue/Reliability Assessment Using iSIGHT, MSC/Nastran and nCode

2005 ◽  
Author(s):  
Thomas Wang ◽  
Xianming Wang ◽  
Maolin Tsai
Keyword(s):  
Reliability Assessment ◽  
Fatigue Reliability ◽  
Structural Fatigue

Fatigue Analysis of Risers

2002 ◽  
Author(s):  
Rommel Burbano Bolan˜os ◽  
Javier Espinosa Rivera ◽  
Dante Campos
Keyword(s):  
Fatigue Analysis ◽  
Ground Movement ◽  
Present Condition ◽  
Structural Safety ◽  
Lateral Stiffness ◽  
Wave Loads ◽  
Fatigue Reliability ◽  
Stress Concentrations ◽  
Study Zone ◽  
Different Diameters

This paper studies the fatigue problem of risers in marine platforms located in the Bay of Campeche, Mexico. Considering the future wave loads on these systems, the lifetime of these structures is obtained. Possibly, these systems have problems of fatigue in the zones where large stress concentrations appear. The risers fatigue analysis with a regular pipeline section is carried out taking into account operational and environmental load conditions. Due to operation, among others, the risers are subject to internal pressure, thermal expansion, and the type of fluid that transports. In order to take into account the environmental conditions one it is considered that the riser is subject to waves, current and ground movement, which were suitably modeled in the analysis. The supports on the platform, in the riser zone, were considered. They take into account the movements and their corresponding lateral stiffness. To evaluate the load cycles to which the risers are subject, for the study zone, the annual rates of occurrence and all the sea states have been considered. In addition, all the possible heights and directions of the wave that might be present in the Bay of Campeche have been considered the accumulated damage caused by the diverse cycles of stresses by means of the Palmgren Miner rule are assessed. This study includes the analysis of representative number of risers with different diameters and recent inspections. This allows us to know, in an approximated way, the present condition of the risers; it an give us suitable information for the calculation of the fatigue reliability and therefore define the present levels of structural safety of these facilities.

Fatigue Reliability Analysis Including Super Long Life Regime

2010 ◽  
Vol 118-120 ◽  
pp. 17-26 ◽  
Author(s):  
Yong Xiang Zhao
Keyword(s):  
Fatigue Life ◽  
Reliability Analysis ◽  
Life Prediction ◽  
Reliability Assessment ◽  
Cyclic Stress ◽  
Fatigue Life Prediction ◽  
Fatigue Reliability ◽  
Stress Strain ◽  
Structural Fatigue ◽  
Long Life

For an engineering structure with an actual fatigue life over that corresponding to a so-called fatigue limit, appropriate reliability assessment and fatigue life prediction are essential for developing the structure and sustaining its high quality in service. Basic clues are explored. A competition fatigue initial mechanism is shown to provide a requirement of material primary quality management. Affordable deduced material and structural probabilistic S-N curves are presented by fitting into material mid-and-long life S-N data and fatigue limits and, then, comparing to structural fatigue limits. Random cyclic stress-strain relations are depicted for constructing random stressing history of structures. Reliability assessment and fatigue life prediction are established to synthetically consider the interference of applied stresses deduced from the random cyclic stress-strain relations and capacity strengths derived from the structural S-N relations with an expected life. Affordable and appropriate method has been then developed to realize the reliability assessment and fatigue life prediction including the super long life regime. Availability of the present method has been indicated through a reliability analysis to the velocity related reliabilities and fatigue lives of a railway axle.

scholarly journals Discussion on Coupling Effect in Structural Load of FOWT for Condensing Wind and Wave Bins for Spectral Fatigue Analysis

2020 ◽  
Vol 8 (11) ◽  
pp. 937
Author(s):  
Tomoya Inoue ◽  
Ahmad Adilah ◽  
Kazuhiro Iijima ◽  
Sho Oh ◽  
Hideyuki Suzuki
Keyword(s):  
Coupling Effect ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Structural Vibration ◽  
Wave Loads ◽  
Frequency Range ◽  
Combined Stress ◽  
Coupling Effects ◽  
Structural Fatigue ◽  
Floating Offshore Wind Turbines

Floating Offshore Wind Turbines (FOWTs) are subject to combined wind and wave loads. The response is not given as a simple sum of the wind-only response and wave-only response due to nonlinear coupling effects, which makes the structural analysis more complex and time-consuming. When a spectral approach for the structural fatigue analysis is considered, it is necessary to accurately estimate the variance of the combined stress taking account of the coupling effect. In this study, firstly the characteristics of the combined response are investigated. It is found out the coupling effects are two-fold; one is the aerodynamic exciting load increase for the forced motion in the wave frequency range. The other is the aerodynamic damping effect due to the increase of the relative wind speed, which is prominent in the structural vibration frequency range. Mathematical models to account for these coupling effects are developed. Then, a series of simulations are performed on three types of FOWTs to validate the models. It is shown that the characteristics of the combined response are different among the three types of the platforms and the developed model can explain the increase/decrease of the variance of the combined stress when compared with two decoupled wave-only and wind-only simulations.

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.

Principal Axes for Structural Fatigue

2005 ◽  
Author(s):  
Bruce L. Hutchison ◽  
Benjamin B. Ackers ◽  
Timothy S. Leach
Keyword(s):  
Time Domain ◽  
Wave Loads ◽  
Time Domain Simulation ◽  
Spectral Moments ◽  
Structural Fatigue ◽  
Time Frequency ◽  
Principal Axes ◽  
Stress Cycles ◽  
Distribution Of Stress

Recent advances in the analysis of joint seakeeping processes are applied to the accumulation of spectral fatigue cycles. The methods of cross co-spectral moments and techniques adopted from the determination of principal angles for seakeeping processes are used to determine orientation of the most severe plane for the accumulation of spectral fatigue cycles and the distribution of stress cycles on that plane. The theory presented considers all aspects of the wave loads experienced over the life of the structure and uses linear theory to predict lifetime fatigue using more efficient techniques than equally comprehensive time-domain simulation. Three methods of determining the orientation of the principal plane and their theoretical differences are discussed. Quantitative comparisons are presented in the time, frequency and probability domains to illustrate differences and demonstrate consistency.

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