Tactical operator guidance to mitigate naval vessel structural fatigue damage

2022 ◽  
Vol 119 ◽  
pp. 103005
Author(s):  
Ian Thompson
Keyword(s):  
Fatigue Damage ◽  
Naval Vessel ◽  
Structural Fatigue

Time Domain Fatigue Life Analysis of Offshore Jacket Structure

2019 ◽  
Author(s):  
Yan Wei Wu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time Domain ◽  
Offshore Wind ◽  
Support Structure ◽  
Structural Fatigue ◽  
Long Time ◽  
Fatigue Life Analysis ◽  
Stress Concentration Factors ◽  
The Time Domain

Abstract Offshore wind system encountered wind, wave, current, soil, and other environmental loads. The support structure is randomly loaded for a long time, which is more likely to cause fatigue damage. In this paper, the NREL 5MW wind turbine and OC4 jacket support structure is selected to perform the time domain fatigue analysis. Commercial software Bladed and SACS are used to perform the required structural responses and fatigue strength calculations. The Stress Concentration Factors (SCF) and S-N curves for the stress calculations of tubular joints are adopted based on the recommendation of DNV GL guidelines. The magnitude of the stress variation range and the corresponding number of counts are obtained by using the rain-flow counting algorithm. Finally, the Palmgren-Miner’s rule is adopted to calculate the cumulative damage ratio and the fatigue life can then be estimated. Fatigue damage ratio and structural fatigue life of each joint during 20 years of operation period are evaluated.

Structural Fatigue Analysis on Expansion Joints of Diversion Penstock of Hydropower Station

2011 ◽  
Vol 117-119 ◽  
pp. 262-268
Author(s):  
Jia Dong ◽  
Gen Hua Yan
Keyword(s):  
Fatigue Damage ◽  
Dynamic Effect ◽  
Water Diversion ◽  
Structural Vibration ◽  
Hydropower Station ◽  
Expansion Joints ◽  
Structural Fatigue ◽  
Safety And Reliability ◽  
Normal Water ◽  
Cumulative Fatigue Damage

Abstract: The section of diversion penstock near the powerhouse behind dam in some hydropower station is equipped with expansion joints, which is used to remedy deformation of penstock in axial and lateral due to the variation of temperature and foundation subsidence. When the hydropower station is in normal water diversion and power generation, the discharged flow generates fluctuating loads, induces structural vibration of guide cylinder of expansion joints, gives rise to cumulative fatigue damage of guide cylinder and also leads to weld joints in guide cylinder cracking to fall off. When generating unit is in the condition of load rejection, expansion joints bears not only the fluctuating pressure loads of the flow, but also undergoes the shock from water-hammer pressure as well, so this demands higher requirement for the safety and reliability of expansion joints structure. It has important engineering value for ensuring safety and reliability of water-diverting power generating system to conduct researches on dynamic effect that fluctuating loads having on expansion joints guide cylinder structure and cumulative fatigue damage of terminal weld of guide cylinder

scholarly journals Multiaxial Fatigue Spectrum Editing by Using Combined Wavelet Analysis and Stress Invariant Approach

2018 ◽  
Vol 165 ◽  
pp. 16009
Author(s):  
Anahita Imanian ◽  
Kelvin Leung ◽  
Nagaraja Iyyer
Keyword(s):  
Fatigue Damage ◽  
Fatigue Testing ◽  
Fatigue Crack Initiation ◽  
Statistical Parameter ◽  
Multiaxial Fatigue ◽  
Loading Path ◽  
Plane Stress Condition ◽  
Structural Fatigue ◽  
Wavelet Transform Analysis ◽  
Parameter Values

The practicalities of structural fatigue testing limit the fidelity of the cyclic load history that can be applied to a test structure. Testing is, therefore, a compromise between fatigue damage fidelity and test economy. A new methodology is proposed for multiaxial loading spectrum editing to extract cycles that contribute negligible damage during fatigue crack initiation. The method is based on projection by projection (PbP) technique and wavelet transform analysis (WTA) procedure. In this approach, the cycles with negligible contribution to damage in every decoupled projected loading path (i.e. obtained from PbP approach) are extracted using the WTA procedure. Each extracted segment is then replaced with an equivalent cycle that produces the same amount of damage. The effectiveness of the edited spectrums is evaluated by the degree of fatigue damage retention as the original damage and preservation of statistical parameter values. As a case study, the proposed approach has been applied to the numerically produced random bending-torsion fatigue spectrum in plane-stress condition. The result shows an average of 75% reduction of the original spectrums with retention of 90% of the original spectrums’ damage values.

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.

Structural Connection Fatigue Evaluation Methodology Using Time Domain Approach

2020 ◽  
Author(s):  
Sagar Samaria ◽  
Bob Zhang ◽  
Sudhakar Tallavajhula ◽  
Johyun Kyoung
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Fatigue Damage ◽  
Time Domain ◽  
Life Extension ◽  
Stress Range ◽  
Repair Work ◽  
Structural Fatigue ◽  
Structural Connections ◽  
Structural Connection

Abstract There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections. To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage. This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.

Research on Structural Fatigue Damage Based on the Superimposed Load Spectrum Method

2013 ◽  
Vol 652-654 ◽  
pp. 1367-1371
Author(s):  
Xiao Ling Shi ◽  
Ji Long Xie ◽  
Fang Wei Zhao ◽  
Rong Quan Yu
Keyword(s):  
Fatigue Damage ◽  
Structural Damage ◽  
Time History ◽  
Actual Situation ◽  
Load Spectrum ◽  
Total Stress ◽  
Structural Fatigue ◽  
Spectrum Method ◽  
Load Sequence ◽  
Total Damage

We usually calculate the fatigue damage by superimposed respective injury; the paper brings up the superimposed load spectrum method considering load sequence. It superimposed on the load spectrum of each load and obtained the total damage of total stress time history. Finally, as an example, bolster’s damage is calculated by two ways. By contrast, the damage is larger by former method. The injury results based on the method of superimposed load spectrum is closer to the actual situation. Therefore, the research method presented in this paper can provide a reference for future structural damage.

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