Ice-Induced Fatigue Analysis by Spectral Approach for Offshore Jacket Platforms with Ice-Breaking Cones

The spectral methods and ice-induced fatigue analysis are discussed based on Miner＇s linear cumulative fatigue hypothesis and S-N curve data. According to the long-term data of full-scale tests on the platforms in the Bohai Sea, the ice force spectrum of conical structures and the fatigue environmental model are established. Moreover, the finite element model of JZ20-2MSW platform, an example of ice-induced fatigue analysis, is built with ANSYS software. The mode analysis and dynamic analysis in frequency domain under all kinds of ice fatigue work conditions are carded on, and the fatigue life of the structure is estimated in detail. The methods in this paper can be helpful in ice-induced fatigue analysis of ice-resistant platforms.

Fatigue Analysis of the Taut-Wire Mooring System Applied for Deep Waters

Precisely predicting the fatigue life of taut-wire mooring systems has become an interesting and important problem for scientists and engineers since there are still difficulties in the inspection and maintenance of mooring lines in a rough sea environment especially in deep waters. In this paper, a comprehensive fatigue analysis is performed for a polyester taut-wire mooring system of an FPSO based on the time domain dynamic theory, rainflow cycle counting method and linear damage accumulation rule of Palmgren-Miner. Three influential factors in the fatigue analysis including the pre-tension, dynamic stiffness and T-N curve are investigated in detail. Two polyester T-N curves, one is from the DNV- 0S-E301 and the other is from the API-RP-2SM, are adopted in the calculation. The fatigue analysis of the mooting system after one-line failure is also carried out. The calculation results indicate that the fatigue life is significantly affected by the T-N curve. The fatigue life decreases with increasing pre-tension, and is largely reduced if taking into account the dynamic stiffness caused by cyclic loading. The analysis also proves that one-line failure has remarkable effects on the fatigue lives of other mooting lines. The present parametric and comparative study is believed to be meaningful to further understanding of the taut-wire mooting system for deepwater applications.

Fatigue Characteristic Analysis of Deepwater Steel Catenary Risers at the Touchdown Point

This paper presents fatigue characteristic analysis of a deepwater steel catenary riser （SCR） under ambient excitations. The SCR involves complex nonlinear dynamic behaviors, especially at the touchdown point （TDP） where the riser first touches the seafloor. Owing to the significant interaction with soil, the touchdown zone is difficnlt to be modeled. Based on Lumped-Mass method and P-y curve, nonlinear springs are used to simulate the SCR-seabed coupled interaction. In case studies, an SCR＇s dynamic features have been obtained by transient analysis and the structure fatigue assessment has been carried out by S-N approach. The comparative analysis shows that the TDP is the key location where soil-riser interaction rises steeply and minimum fatigue life occurs. Parameters such as ocean environment loads, vessel motions, riser material and geometric parameters are discussed. The results indicate that the vessel motion is the principal factor for the structure fatigue life distribution.

Enhanced Multi-Layer Fatigue-Analysis Approach for Unbonded Flexible Risers

This paper proposes an enhanced approach for evaluating the fatigue life of each metallic layer of unbonded flexible risers. Owing to the complex structure of unbonded flexible risers and the nonlinearity of the system, particularly in the critical touchdown zone, the traditional method is insufficient for accurately evaluating the fatigue life of these risers. The main challenge lies in the transposition from global to local analyses, which is a key stage for the fatigue analysis of flexible pipes owing to their complex structure. The new enhanced approach derives a multi-layer stress-decomposition method to meet this challenge. In this study, a numerical model validated experimentally is used to demonstrate the accuracy of the stress-decomposition method. And a numerical case is studied to validate the proposed approach. The results demonstrate that the multi-layer stress-decomposition method is accurate, and the fatigue lives of the metallic layers predicted by the enhanced multi-layer analysis approach are rational. The proposed fatigue-analysis approach provides a practical and reasonable method for predicting fatigue life in the design of unbonded flexible risers.

RELIABILITY ANALYSIS FOR AN AERO ENGINE TURBINE DISK UNDER LOW CYCLE FATIGUE CONDITION

Reliability analysis methods based on the linear damage accumulation law (LDAL) and load-life interference model are studied in this paper. According to the equal probability rule, the equivalent loads are derived, and the reliability analysis method based on load-life interference model and recurrence formula is constructed. In conjunction with finite element analysis (FEA) program, the reliability of an aero engine turbine disk under low cycle fatigue (LCF) condition has been analyzed. The results show the turbine disk is safety and the above reliability analysis methods are feasible.

Full－range nonlinear analysis of fatigue behaviors of reinforced concrete structures by finite element method

The offshore reinforced concrete structures are always subject to cyclic load, such as wave load.In this paper a new finite element analysis model is developed to analyze the stress and strain state of reinforced concrete structures including offshore concrete structures, subject to any number of the cyclic load. On the basis of the anal ysis of the experimental data,this model simplifies the number of cycles-total cyclic strain curve of concrete as three straight line segments,and it is assumed that the stress-strain curves of different cycles in each segment are the same, thus the elastoplastic analysis is only needed for the first cycle of each segment, and the stress or strain corresponding to any number of cycles can be obtained by superposition of stress or strain obtained by the above e lastoplastic analysis based on the cyclic numbers in each segment.This model spends less computer time,and can obtain the stress and strain states of the structures after any number of cycles.The endochronic-damage and ideal offshore concrete platform subject to cyclic loading are experimented and analyzed by the finite element method based on the model proposed in this paper. The results between the experiment and the finite element analysis are in good agreement,which demonstrates the validity and accuracy of the proposed model.

Optimum Autofrettage Pressure of Hydrogen Valve Using Finite Element and Fatigue Analysis

The presented article shows an estimation method of optimum autofrettage pressure taking into consideration subsequent cyclic loading. An autofrettage process is used in pressure vessel applications for strength improvement. The process relies on applying massive pressure that causes internal portions of the part to yield plastically, resulting in internal compressive residual stresses when pressure is released. Later applied working pressure (much lower than autofrettage pressure) creates stress reduced by the residual compressive stress improving the structural performance of the pressure vessels. The optimum autofrettage pressure is a load that maximizes the fatigue life of the structure at the working load. The estimation method of that pressure of a hydrogen valve is the subject of the presented work. Finite element and fatigue analyses were employed to investigate the presented problem. An automated model was developed to analyze the design for various autofrettage pressures. As the results of the procedure, the optimum autofrettage pressure is determined. The research has shown that the developed method can profitably investigate the complex parts giving the autofrettage load that maximizes the fatigue life. The findings suggest that the technique can be applied to a large group of products subjected to the autofrettage process.

PROBABILISTIC METHODOLOGY OF LOW CYCLE FATIGUE ANALYSIS

The cyclic stress-strain responses (CSSR), Neuber's rule (NR) and cyclic strain-life relation (CSLR) are treated as probabilistic curves in local stress and strain method of low cycle fatigue analysis. The randomness of loading and the theory of fatigue damage accumulation (TOFDA) are considered. The probabilistic analysis of local stress, local strain and fatigue life are constructed based on the first-order Taylor's series expansions. Through this method proposed fatigue reliability analysis can be accomplished.

Study on the application of spectral fatigue analysis

Fatigue failure has long been an important issue for ships and offshore structures. Among the numerous methods for predicting fatigue life, the spectral method is accepted as the most reliable. Although the theory behind spectral analysis is straight-forward, the analysis itself is complicated and time-consuming because it is closely related to critical technical details such as the application of fatigue loading (wave pressures and the inertial forces due to cargoes), the extraction of the stress, and the calculation of stress RAO. Here, four key technical details-loading application, displacement boundary condition, the calculation of stress RAO, and the extraction of the fatigue stress-are discussed thoroughly. For each aspect, a resolution is presented based on the finite element pre-and post-processing software MSC/PATRAN or FE solver MSC/NASTRAN. The resolutions are effective and efficient, which can help engineers perform spectral fatigue analysis accurately and faster.

Retrieving Effective Stress Spectrum of Fatigued Components from Fractographic Quantitative Analysis

Under the constant amplitude and pro- grammed loading conditions the fatigued fracture surfaces of 2024-T3 sheet are examined by SEM and TEM.A corrected method,in which the effects of loading sequence are taken into account,has been developed for the retrieval of effective stress spectrum.The parameters including d,a,C,n,R,α and σ_y are evaluated according to their influences on the retrieved results.Several computer programs have been produced for the fractographic quantita- tive analysis,and the application of image pro- cessing technique in the fractographic analysis is al- so interpreted.

Analysis and Comparison of Safety and Fatigue Comfort of Postal Bicycles Based on Finite Element Method and sEMG

The safety and the fatigue comfort were compared between a domestic and a Japanese postal bicycle. Firstly, the fatigue comfort of these two kinds of bicycles was evaluated by surface electromyographic signal (sEMG) experiment, in which human lower limb muscle groups were research objects, and the average EMG (AEMG) index and median frequency (MF) were chosen as the evaluation indexes. Secondly, the safety of these two kinds of bicycle frames was analyzed and compared by using the finite element analysis. The results show that the riding fatigue comfort of the Japanese postal bicycle is better, and the Japanese postal bicycle frame is more safe and reasonable although both the postal bicycles meet the requirement for strength. Finally, based on the above analysis, the frame structure and related parameters of the domestic postal bicycle were improved with reference to the Japanese postal bicycle and biomechanics theory.

An Improved Spectral Analysis Method for Fatigue Damage Assessment of Details in Liquid Cargo Tanks

Errors will be caused in calculating the fatigue damages of details in liquid cargo tanks by using the traditional spectral analysis method which is based on linear system, for the nonlinear relationship between the dynamic stress and the ship acceleration. An improved spectral analysis method for the assessment of the fatigue damage in detail of a liquid cargo tank is proposed in this paper. Based on assumptions that the wave process can be simulated by summing the sinusoidal waves in different frequencies and the stress process can be simulated by summing the stress processes induced by these sinusoidal waves, the stress power spectral density(PSD) is calculated by expanding the stress processes induced by the sinusoidal waves into Fourier series and adding the amplitudes of each harmonic component with the same frequency. This analysis method can take the nonlinear relationship into consideration and the fatigue damage is then calculated based on the PSD of stress. Take an independent tank in an LNG carrier for example, the accuracy of the improved spectral analysis method is proved much better than that of the traditional spectral analysis method by comparing the calculated damage results with the results calculated by the time domain method. The proposed spectral analysis method is more accurate in calculating the fatigue damages in detail of ship liquid cargo tanks.

Proteomics analysis of liver proteins from rats with spleen-deficiency syndrome induced by chronic improper diet consumption and fatigue

Objective:To investigate a proteomics analysis of liver proteins from rats with spleen-deficiency syndrome (SDS) induced by chronic improper diet consumption and fatigue.Methods:This study used a liver proteomic profiling method to identify differentially expressed proteins and altered pathways involved in SDS rats.Specifically,we collected liver samples from a control group and a group with SDS induced by chronic improper diet consumption and fatigue for 4 weeks.The pooled liver proteins in each group were labeled with 8-plex isobaric tags for relative and absolute quantitation reagents.The labeled control and SDS group samples were pooled together and separated by high-pH reverse-phase liquid chromatography.The differentially expressed proteins from the liver proteomes were analyzed to identify potential biomarkers of SDS.Differentially expressed proteins were selected in conjunction with gene ontology and ingenuity pathway analysis.Results:We identified 2176 protein clusters with more than two peptides in the SDS group,with 141 proteins quantified as differentially expressed proteins.Of these,75 proteins were up-regulated,and 66 were down-regulated.Three activated signaling pathways,the thrombin,CXCR4 and synaptic long term depression signaling pathways,and a large multi-protein complex within the network were revealed in the liver proteomic analysis of SDS rats.Conclusions:This is the first report of a differential liver proteome under SDS conditions.The results suggest that the liver proteome partially reflects the pathological changes involved in SDS.The findings provide important information for comprehensively understanding the mechanisms of dysfunction or injury in the liver at the molecular level as a result of SDS.Furthermore,they provide a novel understanding of the connotation of SDS in the fleld of traditional Chinese Medicine.

FINITE ELEMENT ANALYSIS TO THE FATIGUE STRENGTH OF SYNCHRONOUS BELT TEETH

By means of finite element analysis methods calculated the stress, strainand displacement of the belt teeth and analysisied the factors such as load distribution,specific property coefficient of material and temperature variation, which influence the fatigue strength of the belt teeth..

Effects of Exercise on Cancer-related Fatigue and Quality of Life in Prostate Cancer Patients Undergoing Androgen Deprivation Therapy: A Meta-analysis of Randomized Clinical Trials

Objective To gain insight on how exercise affects the outcomes of prostate cancer patients treated with androgen deprivation therapy,specifically cancer-related fatigue(CRF) and quality of life(QoL). Methods Systematic searches for randomized clinical trials(RCTs) evaluating the effects of exercise on CRF and QoL of prostate cancer patients receiving androgen deprivation therapy were carried out to identify the eligible studies from EMBASE,Pub Med and Cochrane library. Related data were extracted from eligible studies and then subjected to Reviewer Manage 5.3 for analysis. Standardized mean differences(SMD) and its 95% confidence interval(CI) were calculated. Results In all,10 RCTs involving 841 prostate cancer patients(448 of whom exercised and 393 did not) were included in this study. With respect to CRF,there was good consistency among different studies,and it was remarkably reduced in the exercise group(SMD=-0.32,95% CI:-0.45 to-0.18,P<0.00001,n=784). In regards to QoL,there was also good consistency among different studies,and it was also improved significantly in the exercise group(SMD=0.21,95% CI:0.08 to 0.34,P=0.002,n=841). Conclusion Exercise both reduced CRF and improved QoL in prostate cancer patients receiving androgen deprivation therapy.

sEMG Feature Analysis on Forearm Muscle Fatigue During Isometric Contractions

In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects,and recorded the sEMG signals of the flexor carpi ulnaris.sEMG's median frequency(MDF) and mean frequency(MF) were extracted by short term Fourier transform(STFT),and the root mean square(RMS) of wavelet coefficients in the frequency band of 5—45 Hz was obtained by continuous wavelet transform(CWT).The results demonstrate that both MDF and MF show downward trends within 1 min; however,RMS shows an upward trend within the same time.The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8.It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.

Fatigue Analysis and Life Prediction of Dumpers with Cumulative Fatigue Damage Approach

A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element analysis is carried out for assessing stress distribution and strength characteristics of dumpers. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule. The investigation shows that fatigue notch factor has a significant influence on the calculation of fatigue damage of dumpers.

Multi-Scale Analysis of Fretting Fatigue in Heterogeneous Materials Using Computational Homogenization

This paper deals with modeling of the phenomenon of fretting fatigue in heterogeneous materials using the multi-scale computational homogenization technique and finite element analysis(FEA).The heterogeneous material for the specimens consists of a single hole model(25% void/cell,16% void/cell and 10% void/cell)and a four-hole model(25%void/cell).Using a representative volume element(RVE),we try to produce the equivalent homogenized properties and work on a homogeneous specimen for the study of fretting fatigue.Next,the fretting fatigue contact problem is performed for 3 new cases of models that consist of a homogeneous and a heterogeneous part(single hole cell)in the contact area.The aim is to analyze the normal and shear stresses of these models and compare them with the results of the corresponding heterogeneous models based on the Direct Numerical Simulation(DNS)method.Finally,by comparing the computational time and%deviations,we draw conclusions about the reliability and effectiveness of the proposed method.

Nonlinear Dynamic Analysis and Fatigue Study of Steep Wave Risers Under Irregular Loads

As a reliable alternative option for traditional steel catenary risers(SCRs),steep wave risers(SWRs)have been widely applied to deepwater oil and gas production.However,the nonlinear dynamic analysis of SWRs is more complicated than that of traditional SCRs due to their special configuration and significant geometric nonlinearity.Moreover,SWRs are highly susceptible to fatigue failure under the combined excitation of irregular waves and top floater motions(TFMs).In this study,considering irregular waves and TFMs,a numerical SWR model with an internal flow is constructed based on the slender rod model and finite element method.The Newmark-βmethod is adopted to solve the dynamic behavior of SWR.Moreover,the Palmgren-Miner rule,a specified S-N curve,and rainflow counting method are applied to estimate the fatigue damage.An efficient numerical computation procedure,i.e.,DRSWR,is programmed with MATLAB in this study.Calculation results are compared with those of OrcaFlex to verify the accuracy of the DRSWR.The nonlinear dynamic response and fatigue damage of an SWR under the combined excitation of irregular waves and TFMs are obtained,and a comprehensive parametric analysis is then conducted.The analysis results show that the buoyancy section undergoes the highest level of stress and fatigue damage under the combined excitation of irregular waves and TFMs.An internal flow with high velocity and high density produces a high level of fatigue damage.The buoyancy factor and length of the buoyancy section should be set moderately to reconcile the reduction of the top tension with increased fatigue life.These results are expected to provide some reference significance for the engineering design of SWR.