Improvement of trawler hull structure under condition of ensuring fatigue strength

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.

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

International Journal of Structural Integrity ◽

10.1108/ijsi-04-2014-0017 ◽

2016 ◽

Vol 7 (2) ◽

Cited By ~ 5

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.

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Fatigue Life Assessment of Offshore Patrol Vessel

Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B ◽

10.1115/omae2009-79005 ◽

2009 ◽

Cited By ~ 1

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.

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Study on the Remaining Fatigue Life of FPSO Based on Spectral Analysis

Volume 3A: Structures, Safety and Reliability ◽

10.1115/omae2017-61428 ◽

2017 ◽

Author(s):

Lei Yu ◽

Huilong Ren ◽

Xudong Liu ◽

Xiaoxiong Sun ◽

Yakang Peng

Keyword(s):

Spectral Analysis ◽

Fatigue Life ◽

Fatigue Damage ◽

Failure Modes ◽

Hot Spot ◽

Stress Transfer ◽

Three Dimensional Model ◽

Hot Spot Stress ◽

Hull Structure ◽

Remaining Fatigue Life

The fatigue failure, as one of the traditional failure modes of ship hull structures [1], has been widely concerned in recent years. For FPSO converted from large oil tankers, it is critical to predict and extend their service life. The analysis has been finished in compliance with the fatigue damage calculation procedure on the basis of spectral method. A three dimensional model has been performed to represent the entire hull structure. The Hot-Spot Stress Approach is employed to determine the stress transfer function for a location where the fatigue strength is to be evaluated. The fatigue damage resulting from combining the damage from each of the short-term conditions can be accomplished by the use of a weighted liner summation technique. The remaining fatigue life of the FPSO is calculated by the method of spectral analysis to determine the fatigue damage of the oil tanker during the operation period and the FPSO working period respectively. According to the results, the inspection and maintenance of hull structures can be effectively carried out.

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A Method for Fatigue Evaluation of Trimaran Cross Structure With the Influence of Slamming

Volume 3A: Structures, Safety and Reliability ◽

10.1115/omae2017-62492 ◽

2017 ◽

Author(s):

Zhe Li ◽

Huilong Ren ◽

Kai Jin

Keyword(s):

Stress Response ◽

Fatigue Strength ◽

Fatigue Damage ◽

Linear Response ◽

Operating Conditions ◽

Wave Load ◽

Hull Structure ◽

Non Linear ◽

Slamming Load ◽

Cross Structure

Slamming is a highly non-linear phenomenon between hull structure and wave. Due to the special structure of trimaran, the slamming mode is extremely different from that of traditional vessel. Besides bow emergence and enter, the slamming phenomenon of the out shell at the cross structure is also obvious. In conventional hull structure fatigue strength evaluation, the slamming load is usually not considered. However, the slamming problem is unavoidable at danger load cases, and the stress concentration of the trimaran cross structure is serious. So it is dangerous to ignore the existence of slamming in serious load cases when evaluating the structural fatigue strength. Therefore, it is necessary to study the contribution of slamming load to fatigue damage. In this paper, a practical method for calculating and analyzing is presented to consider the effect of slamming on the fatigue strength of the trimaran cross structure to ensure that the fatigue life of the structure is closer to the true value. According to the linear theory, the relative motion and relative speed of the hull in wave and the stress response of the wave load on the structure are calculated firstly. Then, the stress response of the non-linear out shell slamming force is calculated. The linear response and non-linear response are combined. And the stress response time history under the combined action of slamming and wave load are obtained. Finally, the fatigue damage of the structure under dangerous operating conditions is calculated by the rain flow counting method. And the contribution value of the slamming load to the structural damage degree is calculated. The paper will put forward some reference suggestions for fatigue study calculation and evaluation of Trimaran cross structure with the influence of slamming.

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

Volume 4B: Structures, Safety and Reliability ◽

10.1115/omae2014-24228 ◽

2014 ◽

Cited By ~ 2

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.

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Fatigue Damage Estimation of Welded Joints Considering Mechanochemical Interaction

Volume 3A: Structures, Safety and Reliability ◽

10.1115/omae2017-62315 ◽

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.

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Fatigue Strength Curve for Tubular Joints of Offshore Structures under Dynamic Loading

Dynamics ◽

10.3390/dynamics1010007 ◽

2021 ◽

Vol 1 (1) ◽

pp. 125-133

Author(s):

Sudath C. Siriwardane ◽

Nirosha D. Adasooriya ◽

Dimitrios Pavlou

Keyword(s):

Fatigue Strength ◽

Hot Spot ◽

Offshore Structures ◽

Hot Spot Stress ◽

Tubular Joints ◽

Jacket Structures ◽

Strength Curve ◽

Tubular Joint ◽

Stress Concentration Factors

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

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Fatigue Strength Assessment of the Cruciform Fillet Welded Joint Using Hot-spot Stress Approach

Transactions of the Korean Society of Mechanical Engineers A ◽

10.3795/ksme-a.2005.29.11.1488 ◽

2005 ◽

Vol 29 (11) ◽

pp. 1488-1493 ◽

Cited By ~ 2

Author(s):

Chang-Sung Seok ◽

Dae-Jin Kim ◽

Jae-Mean Koo ◽

Jung-Won Seo ◽

Byeong-Choon Goo

Keyword(s):

Fatigue Strength ◽

Welded Joint ◽

Hot Spot ◽

Hot Spot Stress ◽

Strength Assessment ◽

Fatigue Strength Assessment

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Fatigue Assessment of Trimaran Structure Based on Simplified Procedure

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.525-526.333 ◽

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).

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