Fatigue Reliability Analysis for Brace–Column Connection Details in a Semisubmersible Hull1

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Dilnei Schmidt ◽  
Lance Manuel ◽  
Hieu H. Nguyen ◽  
Luis V. S. Sagrilo ◽  
Edison C. Prates de Lima
Keyword(s):  
Reliability Analysis ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Response Spectra ◽  
Life Assessment ◽  
Response Analysis ◽  
Fe Model ◽  
Fatigue Reliability ◽  
Hot Spot Stress ◽  
Axial Forces

Semisubmersible floating platforms used in offshore deep or ultradeep water environments have hull structures that are comprised of vertical cylinders (columns) connected by braces, pontoons, etc. Several of the connections between these various members are susceptible to fatigue damage. In fatigue damage assessment or fatigue reliability analysis, a global structural response analysis is typically carried out using a finite element (FE) model where internal forces or stresses in the various members are evaluated for specified sea states measured at the site. Of specific interest in the present study is the fatigue reliability analysis of brace-column connection details in a semisubmersible hull unit for selected Brazilian environmental conditions. Stress concentration factors (SCFs) for the selected critical hot spots are applied to the nominal component stresses due to axial forces and biaxial bending. The hot-spot stress response spectra are used with various spectral methods—referred to as Rayleigh, modified Rayleigh (with bandwidth correction), and Dirlik—to estimate fatigue damage using Miner's rule. Uncertainties in some parameters used in the fatigue life assessment are considered and the probability of fatigue failure in the last operational year of the structure is estimated.

Fatigue Reliability Assessment for Brace-Column Details in a Semi-Submersible Hull

2014 ◽  
Author(s):  
Dilnei Schmidt ◽  
Lance Manuel ◽  
Hieu H. Nguyen ◽  
Luis Volnei Sudati Sagrilo ◽  
Edison Castro Prates de Lima
Keyword(s):  
Reliability Analysis ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Response Spectra ◽  
Element Model ◽  
Response Analysis ◽  
Fatigue Reliability ◽  
Hot Spot Stress ◽  
Axial Forces ◽  
Uncertainty Estimates

Semi-submersible floating platforms used in the offshore deepwater environment have hull structures that are comprised of vertical cylinders (columns) connected by braces, pontoons, etc. Several of the connections between these various members are susceptible to fatigue damage. In fatigue damage assessment or fatigue reliability analysis, a global structural response analysis is typically carried out using a finite element model where internal forces or stresses in the various members are evaluated for specified sea states of interest at the site. Of specific interest in this study is the fatigue reliability analysis of brace-column connection details in a semi-submersible hull unit for selected Brazilian environmental conditions. Stress concentration factors for the selected critical hot spots are applied to the nominal component stresses due to axial forces and biaxial bending. The hot-spot stress response spectra are used with various spectral methods — referred to as Rayleigh, Modified Rayleigh (with bandwidth correction), and Dirlik — to estimate fatigue damage using Miner’s rule. Uncertainty estimates in fatigue damage rates and life based on the various methodologies are discussed and critical sea states are identified, highlighting dynamic and quasi-static influences on the predicted fatigue.

Fatigue strength assessment of ship structures accounting for a coating life and corrosion degradation

2016 ◽  
Vol 7 (2) ◽  
Author(s):  
Yordan Garbatov
Keyword(s):  
Finite Element ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Limit State ◽  
State Function ◽  
Fatigue Reliability ◽  
Hot Spot Stress ◽  
Notch Stress ◽  
Fatigue Limit State

Purpose Fatigue strength and reliability assessment of complex double hull oil tanker structures, based on different local structural finite element approaches, is performed accounting for the uncertainties originating from load, nominal stresses, hot spot stress calculations, weld quality estimations and misalignments and fatigue S-N parameters including the correlation between load cases and the coating life and corrosion degradation. Design/methodology/approach Ship hull wave-induced vertical and horizontal bending moments and pressure are considered in the analysis. Stress analyses are performed based on the nominal, local hot spot and notch stress approaches. A linear elastic finite element analysis is used to determine the stress distribution around the welded details and to estimate structural stresses of all critical locations. Fatigue damage is estimated by employing the Palmgren-Miner approach. The importance of the contribution of each random variable to the uncertainty of the fatigue limit state function is also estimated. The probability of fatigue damage of hot spots is evaluated taking into account random coating life and corrosion wastage. Fatigue reliability, during the service life, is modelled as a system of correlated events. Findings The fatigue analysis showed that the fatigue damage at the hotspot, located at the flange of the stiffener close to the cut-out, is always highest in the cases of the structural hot spot stress and effective notch stress approaches, except for the one of the nominal stress approach. The sensitivities of the fatigue limit state function with respect to changes in the random variables were demonstrated showing that the uncertainty in the fatigue stress estimation and fatigue damage are the most important. Fatigue reliability, modelled as a parallel system of structural hot spots and as a serial system of correlated events (load cases) was evaluated based on the Ditlevsen bounds. As a result of the performed analysis, reliability and Beta reliability indexes of lower and upper bounds were estimated, which are very similar to the ones adopted for ultimate strength collapse as reported in literature. Originality/value This paper develops a very complex fatigue strength and reliability assessment model for analysing a double hull oil tanker structure using different local structural finite element approaches accounting for the associated uncertainties and the correlation between load cases and the coating life and corrosion degradation. The developed model is flexible enough to be applied for analysing different structural failure modes.

Fatigue of Ship Structural Details—Technical Development and Problems

1997 ◽  
Vol 41 (04) ◽  
pp. 318-331
Author(s):  
Tao Xu
Keyword(s):  
Fatigue Damage ◽  
Hot Spot ◽  
Fatigue Loading ◽  
Technical Development ◽  
Fatigue Reliability ◽  
Random Loading ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Technical Developments ◽  
Structural Details

During the past five years, a joint industry-government sponsored research project titled the Ship Structural Maintenance Project (SMP) has been conducted at the Department of Naval Architecture & Offshore Engineering, University of California at Berkeley. As a part of this project, the fatigue damage of ship structural details has been extensively studied. This paper summarizes the technical development in fatigue assessment of ship structural details developed during this project. In the fatigue resistance model, the fatigue damage evaluation of structural details was based on a stress range/number-of-cycles-to-failure (SN) approach in which the nominal stress procedure and the hot spot stress procedure were employed. The fatigue assessment of cracked structural details was based on a cracked SN approach developed by a hybrid SN-FM (fracture mechanics) methodology. This cracked SN approach was further developed to incorporate load-shedding effects. In the fatigue loading model, a new formula for the damage correction factor associated with a wide-banded load process was developed. The random loading sequence for ship service was addressed. Fatigue reliability models were then reviewed and the different fatigue reliability updating procedures were evaluated. These techniques were employed in the fatigue analysis of structural details in three tankers. Analysis results from these three ships were presented to illustrate the technical developments and problems associated with fatigue assessment of ship structural details.

Fatigue Life Assessment of Offshore Patrol Vessel

2009 ◽  
Author(s):  
Asokendu Samanta ◽  
P. Kurinjivelan
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Design Guidelines ◽  
Life Assessment ◽  
Strength Analysis ◽  
Hot Spot Stress ◽  
Critical Locations

Fatigue is a phenomenon, which needs to be considered in the present day’s vessel design. The welded joints are particularly affected by the fatigue damage due to high stress concentrations caused by the metallurgical discontinuities present in the weld. For oil tankers and bulk carriers adequate guidelines for the fatigue strength assessment have been established by the classification societies. But for navy vessel, like offshore patrol vessel, the design guidelines for the fatigue strength analysis are not widely available. In the present paper, an attempt has been made to calculate the fatigue life of offshore patrol vessel (OPV). In general five stages of work is involved in calculating fatigue life of any ship structure. These are, load calculation, nominal and hot spot stress computation, long-term stress distribution, selection of S-N curve and the fatigue damage calculation. In the present study, the wave loads are obtained by the rule based estimation. The finite element analysis with the submodeling approach has been used to get the hot spot stress at critical locations. The two-parameter Weibull curve has been used to get the long-term distribution of stress. And at the end, the fatigue damage and the fatigue life have been computed using the Palmgren-Miner linear cumulative damage theory at the critical locations of the vessel.

scholarly journals Improvement of trawler hull structure under condition of ensuring fatigue strength

2021 ◽  
Vol 4 (7(112)) ◽  
pp. 50-59
Author(s):  
Leontii Korostylov ◽  
Dmytro Lytvynenko ◽  
Hryhorii Sharun ◽  
Ihor Davydov
Keyword(s):  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Fatigue Cracks ◽  
Bending Moment ◽  
Theoretical Method ◽  
Corrosive Wear ◽  
Hot Spot Stress ◽  
Hull Structure ◽  
Internal Forces

The structure of the hull of the project 1288 trawler in a region of fore hold was improved to ensure fatigue strength of assemblies of the intersection of main frames with the second bottom. To this end, a study of the fatigue strength of these assemblies was carried out for the original side structure and two versions of its modernization. Values of internal forces at the points of appearance of fatigue cracks in the compartment have been determined for three design versions of the side. It was found that the greatest forces act in the middle of the fore half of the compartment. Calculations of parameters of the long-term distribution of magnitudes of ranges of total equivalent operating stresses according to the Weibull law in the points of occurrence of fatigue cracks for different design versions of the side grillage have been performed. These parameters were determined for the middle of the fore hold of the vessel and for the areas in which maximum values of bending moment ranges are in effect with and without corrosive wear. Values of total fatigue damage and durability of the studied assemblies were determined. Calculations were carried out by nominal stress method, hot spot stress method, and experimental and theoretical method. It was shown that in order to ensure fatigue strength of the assembly under consideration, it is necessary to extend the intermediate frames of the original version of the side structure to the level of the second bottom fixing them to the deck. It is also necessary to attach a cargo platform to the side thus reducing the frame span. As a result, the level of fatigue damage over 25 years of operation will decrease by about 3.5 times. As it was found, approximate consideration of the slamming effect does not significantly increase the amount of fatigue damage to the assembly. The results of the development of recommendations for modernization of the side structure can be implemented both on ships of the 1288 project and on other ships with a transverse side framing system.

scholarly journals Use of 3D Scan of Weld Joint in Finite Element Analysis and Stochastic Analysis of Hot-Spot Stresses in Tubular Joint for Fatigue Life Estimation

2019 ◽  
Author(s):  
Mikkel L. Larsen ◽  
Vikas Arora ◽  
Marie Lützen ◽  
Ronnie R. Pedersen ◽  
Eric Putnam
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Welded Joints ◽  
Hot Spot ◽  
Strain Range ◽  
Fe Model ◽  
Design Codes ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Weld Toe

Abstract Several methods for modelling and finite element analysis of tubular welded joints are described in various design codes. These codes provide specific recommendations for modelling of the welded joints, using simple weld geometries. In this paper, experimental hot-spot strain range results from a full-scale automatically welded K-node test are compared to corresponding finite element models. As part of investigating the automatically welded K-joint, 3D scans of the weld surfaces have been made. These scans are included in the FE models to determine the accuracy of the FE models. The results are compared to an FE model with a simple weld geometry based on common offshore design codes and a model without any modelled weld. The results show that the FE model with 3D scanned welds is more accurate than the two simple FE models. As the weld toe location of the 3D scanned weld is difficult to locate precisely in the FE model and as misplacement of strain gauges are possible, stochastic finite element modelling is performed to analyse the resulting probabilistic hot-spot stresses. The results show large standard deviations, showing the necessity to evaluate the hot-spot stress method when using 3D scanned welds.

Strain-Based Fatigue Reliability Analysis of a Load-Carrying Fillet Welded Cruciform Joint

2018 ◽  
Author(s):  
Yan Dong ◽  
Yordan Garbatov ◽  
C. Guedes Soares
Keyword(s):  
Reliability Analysis ◽  
Fatigue Damage ◽  
Local Strain ◽  
Fatigue Reliability ◽  
Response Surface Models ◽  
Surface Models ◽  
Load Carrying ◽  
Fatigue Notch Factor ◽  
Weld Root ◽  
Cruciform Joint

The objective of this work is to perform a fatigue reliability analysis of a load-carrying fillet welded cruciform joint based on the local strain approach. The effective notch stresses of the weld root and toe of the cruciform joint, where the fatigue cracks are usually initiated, are estimated by the finite element method and the fatigue notch factors of these two locations as a function of the weld leg and slit lengths are explicitly represented by response surface models. Within the context of the local strain approach, a critical fatigue notch factor that can exactly trigger fatigue failure is proposed. The statistical descriptors of the critical fatigue notch factor are determined by using the Monte Carlo simulation method, in which the nominal stress range, material properties and fatigue damage at failure are treated as random variables. The limit state functions of the weld root and toe are formulated based on the response surface models and critical fatigue notch factors. The first order reliability method is applied to evaluate the reliability against the fatigue damage. Finally, the cruciform joint system, composed by the two fatigue-prone locations, is evaluated as a series system of components.

Fatigue Damage Estimation of Welded Joints Considering Mechanochemical Interaction

2017 ◽  
Author(s):  
Gang Liu ◽  
Yi Huang ◽  
Qi Zhang ◽  
Zhiyuan Li ◽  
Jingjie Chen ◽  
...  
Keyword(s):  
Corrosion Rate ◽  
Fatigue Damage ◽  
Coupling Effect ◽  
Hot Spot ◽  
Plate Thickness ◽  
High Stress ◽  
Uniform Corrosion ◽  
Hot Spot Stress ◽  
Butt Weld ◽  
Applied Loading

The high stress region around weld joints accelerates corrosion and may induce non-uniform corrosion. In this study, the effect of loading on corrosion behavior of the steel in NaCl solution was investigated. The relationship between the corrosion rate and applied loading was deduced based on the electrochemical theory. Electrochemical experiments were carried out to investigate the interaction between loading and corrosion rate on Q235 steel. A butt weld joint of ship deck structure was selected as a case study. Time-dependent stress concentration factor of welded joint as a function of the corrosion deterioration was analyzed, and the iterative process of stress and corrosion degeneration of plate thickness was used to simulate the coupling effect based on results of the experiment. The hot spot stress approach was adopted to calculate the fatigue damage.

Fatigue Assessment of Trimaran Structure Based on Simplified Procedure

2012 ◽  
Vol 525-526 ◽  
pp. 333-336
Author(s):  
Hui Long Ren ◽  
Shehzad Khurram ◽  
Chun Bo Zhen ◽  
Khurram Asifa
Keyword(s):  
Fatigue Damage ◽  
High Speed ◽  
Hot Spot ◽  
Mathematical Formulation ◽  
Direct Calculation ◽  
Assessment Procedure ◽  
Hot Spot Stress ◽  
Fatigue Assessment ◽  
Strength Assessment ◽  
Simplified Procedure

In recent years, Trimaran platform design has got the attention of naval architects owing to its superior seagoing performance. Trimaran structure experiences severe loads due to its unique configuration and high speed, causing stress concentration, especially in cross deck region and accelerate fatigue damage. This paper presents fatigue strength assessment of Trimaran structure by simplified procedure. A methodology is proposed to evaluate fatigue loads and loading conditions by load combinations of direct calculation procedure of Lloyds Register Rules for Classification of Trimaran (LR Rules). Global FE analysis, in ANSYS, is performed to investigate the stress response. The stress range is computed by hot-spot stress approach, and its long term distribution is specified by Weibull distribution. Fatigue damage of selected critical details is calculated using mathematical formulation of simplified fatigue assessment procedure of Common Structure Rules (CSR).

Sign in / Sign up

Export Citation Format

Share Document