Ultimate Strength and Structural Reliability Analysis of FPSO Hull Girder

2002 ◽  
Author(s):  
Eldho Paul ◽  
Appapillal Thavalingam ◽  
Pumendu K. Das
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Cross Section ◽  
Structural Reliability ◽  
Strength Analysis ◽  
State Function ◽  
Ultimate Capacity ◽  
Hull Girder ◽  
Structural Reliability Analysis ◽  
Wave Induced

The aim of this paper is to provide some results from an investigation on available simplified formulations for ultimate strength analysis of the gull girder and the possibility of extending these methods in order to couple with reliability computations. This particular study is based on an analytical method proposed by Paik and Mansour. The procedure is enhanced to include structural reliability analysis of FPSOs based on probabilistic approach where uncertainties for both capacity and loading of the structure are taken into account. The estimation of the Ultimate longitudinal capacity and the probability of failure of the FPSO are carried out by dividing the cross section of the hull girder into beam column elements considering the different loads acting on the hull. The limit state function is formulated considering the loads acting on the hull girder and ultimate capacity. The ultimate capacity of the hull is taken as a function of variety of random variable (e.g. area of cross section and yield stresses of the different ship components, etc). The loads acting on the hull girder, both still water and wave induced are calculated using IACS and DNV rules and margins are provided to take care of the long-term deployment of FPSO at sea. Some results from the sensitivity analysis are also provided which has been carried out to study the influence of several factors on the structural reliability of the ship under extreme wave induced bending moment loads.

The application of Structural Reliability Analysis on hull girder ultimate strength of bulk carriers-a trial on Safety Level Approach

2015 ◽  
Author(s):  
Daokun Zhang ◽  
Wenyong Tang
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Structural Reliability ◽  
Safety Level ◽  
Hull Girder ◽  
Structural Rules ◽  
Structural Reliability Analysis ◽  
Trial Analysis ◽  
Bulk Carriers ◽  
Partial Safety Factors

The International Maritime Organization is developing the Goal Based Standard, in which the Safety Level Approach(SLA) is one of the two parallel ways forward focusing on deriving explicit and reasonable safety level. During the development of Safety Level Approach, the Structural Reliability Analysis(SRA) is recognized as one of the useful tools. The application of SRA on the calibration of partial safety factors for hull girder ultimate strength is so far a typical illustration, which could be very helpful for the application of Safety Level Approach on the structural Rules in the future. China Classification Society (CCS) carries out a trial analysis with co-operation of Shanghai Jiao Tong University.

The Effect of Sloshing in Tanks on Motions and Hull Girder Responses of Damaged Vessels

2011 ◽  
Author(s):  
Huirong Jia ◽  
Torgeir Moan
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Bending Moment ◽  
Roll Motion ◽  
Multimodal Approach ◽  
Rectangular Shape ◽  
Hull Girder ◽  
Structural Reliability Analysis ◽  
Oil Tankers

The structural reliability analysis of damaged vessels has up to now commonly been investigated by neglecting the effect of sloshing. This paper deals with the effect of sloshing in tanks on motions and hull girder responses of oil tankers in various damage conditions and represents a part of a study to assess the effect of sloshing on hull girder failure of damaged vessels, The flooded tanks are assumed to have a of rectangular shape and linear multimodal approach is adopted to deal with sloshing. It is concluded that even though the effect of sloshing in tanks on the roll motion of vessels can be neglected in certain damage conditions, the effect of sloshing on the horizontal bending moment cannot be neglected, especially when resonance motion occurs.

On the Application of Structural Reliability Analysis

2017 ◽  
Author(s):  
Torfinn Hørte ◽  
Gudfinnur Sigurdsson
Keyword(s):  
Reliability Analysis ◽  
Structural Engineering ◽  
Structural Reliability ◽  
Limit State ◽  
Design Analysis ◽  
Ultimate Limit State ◽  
Hull Girder ◽  
Structural Reliability Analysis ◽  
Code Calibration ◽  
Calculated Probability

Structural Reliability Analysis (SRA) is a useful tool in structural engineering. Uncertainty in input parameters and model uncertainties in the analysis predictions are explicitly modelled by random variables. With this methodology, the uncertainties involved are handled in a consistent and transparent way. Compared to a deterministic analysis, SRA provides improved insight in how the various uncertainties involved influence the results. The main results from SRA is the calculated probability of structural failure, but other useful results such as uncertainty importance factors and design points being the most likely combination of all variables at failure represent helpful information. The present paper illustrates some the features using SRA for two different types of application. The first application is the use of SRA as a tool for code calibration and the second shows the application of SRA to a problem where common practice is likely to be rather conservative and therefore leading to unacceptable results, but where the degree of conservatism is not known. Two examples are chosen to illustrate code calibration; i.e. hull girder ultimate limit state (ULS) for tankers and ULS for mooring design in the ULS for floating offshore vessels. Code calibration involves both SRA and design analysis following the code. It is shown how the design analysis can be modified in order to better reflect a chosen target reliability level across a selected set of test cases representative for what the code should cover. Fatigue of subsea wellhead systems is selected as an example of a special case when application of existing rules may lead to unsatisfactory results which are likely to be rather conservative. It is shown how results can be presented in terms of the accumulated probability of fatigue failure as a function of time. This may be a more suitable basis for decision making than a calculated fatigue life from a standard analysis. It is also illustrated how importance factors from the SRA can be used as guidance on how to prioritize effort in order to improve prediction of the fatigue damage. The present paper is not intended to be detailed in all input and analysis methodology, but draw the attention towards the possibilities and benefits of applying SRA in structural engineering, where the examples are used to illustrate this potential.

A New Response Surface Method for Structural Reliability Analysis

2013 ◽  
Vol 712-715 ◽  
pp. 1506-1509 ◽  
Author(s):  
Guang Bo Li ◽  
Guang Wei Meng ◽  
Feng Li ◽  
Li Ming Zhou
Keyword(s):  
Reliability Analysis ◽  
Response Surface ◽  
Response Surface Method ◽  
Failure Probability ◽  
Structural Reliability ◽  
Uniform Design ◽  
State Function ◽  
Structural Reliability Analysis ◽  
Surface Method ◽  
Reliability Method

The response surface method is adopted to analyze the structural reliability. This paper presents a new response surface method with the uniform design method to predict the failure probability of structures. It is the response surface method based on Fourier orthogonal basis function (RSM-Fourier). To reduce computational costs in structural reliability analysis, approximate Fourier response surface functions for reliability assessment have been suggested. The method involves the selection of training datasets for establishing a model by the uniform design points, the approximation of the limit state function by the trained model and the estimation of the failure probability using first-order reliability method (FORM). The proposed method is applied to examples, compared with other methods to demonstrate its effectiveness.

Bayesian Approach for Structural Reliability Analysis and Optimization Using the Kriging Dimension Reduction Method

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Jooho Choi ◽  
Dawn An ◽  
Junho Won
Keyword(s):  
Dimension Reduction ◽  
Reliability Analysis ◽  
Bayesian Approach ◽  
Structural Reliability ◽  
Reduction Method ◽  
Epistemic Uncertainty ◽  
Limit State ◽  
State Function ◽  
Dimension Reduction Method ◽  
Structural Reliability Analysis

An efficient method for a structural reliability analysis is proposed under the Bayesian framework, which can deal with the epistemic uncertainty arising from a limited amount of data. Until recently, conventional reliability analyses dealt mostly with the aleatory uncertainty, which is related to the inherent physical randomness and its statistical properties are completely known. In reality, however, epistemic uncertainties are prevalent, which makes the existing methods less useful. In the Bayesian approach, the probability itself is treated as a random variable of a beta distribution conditional on the provided data, which is determined by conducting a double loop of reliability analyses. The Kriging dimension reduction method is employed to promote efficient implementation of the reliability analysis, which can construct the PDF of the limit state function with favorable accuracy using a small number of analyses. Mathematical examples are used to demonstrate the proposed method. An engineering design problem is also addressed, which is to find an optimum design of a pigtail spring in a vehicle suspension, taking material uncertainty due to limited test data into account.

Temperature Effects on FPSO Ultimate Strength: A Reliability Based Approach

2003 ◽  
Author(s):  
Ioannis Moatsos ◽  
Purnendu K. Das
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Temperature Effects ◽  
Structural Reliability ◽  
Combination Method ◽  
Structural Safety ◽  
Hull Girder ◽  
Reliability Method ◽  
The Subject ◽  
Effects Of Temperature

Structural Reliability analysis is based on probability theory and a significant amount of literature exists on the subject and continues to be a subject of ongoing research. When the structural safety of a ship’s hull is considered, the ultimate hull girder strength should be evaluated. Existing literature on the subject often neglects the effect of temperature. This paper aims to determine the effects of temperature in ship structural reliability and to propose a procedure for analysing structures by taking into account temperature effects. The ultimate strength of the hull girder was calculated using a component approach, where the behaviour of the hull is evaluated based on the behaviour of the single structural components. A sample analysis for Tanker/FPSO structures is provided where the reliability analysis was carried out using a First and Second Order Reliability Method (FORM and SORM) analysis. The loading component was handled using extreme wave statistics and the Ferry Borges-Castanheta load combination method. Annual reliability indices and probabilities of failure were calculated for hogging and sagging conditions showing the effects of temperature along with Partial Safety Factors for all variables taken into account.

Structural Reliability Analysis Applied on Steel Ships for Rule Partial Safety Factors Calibration

2017 ◽  
Author(s):  
Alexis Benhamou ◽  
Quentin Derbanne ◽  
Jérôme de Lauzon
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Structural Reliability ◽  
Bending Moment ◽  
Safety Factors ◽  
Structural Rules ◽  
Structural Reliability Analysis ◽  
Reliability Method ◽  
Partial Safety Factors ◽  
Common Structural Rules

Ultimate strength assessments in current IACS Common Structural Rules (CSR) are determined by a limited number of constant partial safety factors (PSF). These coefficients are inherited from the previous Common Structural Rules for Oil Tankers, and were determined using a structural reliability analysis (SRA) based on a limited number ship. The authors decided to lead a more comprehensive structural reliability analysis to propose and discuss a new set of rule formulations. A literature review is carried out in order to determine an extensive database of virtual ships covering the whole range of existing ships with a few representative parameters. SRA is applied for ultimate strength assessment on this database. Uncertainties are modeled by a set of probability distributions applied to each characteristic quantity (still water bending moment, wave bending moment and capacity) and a Second Order Reliability Method (SORM) is used to target the ultimate capacity corresponding to a given failure probability for each ship. A set of several PSF formulations are then derived from these results using both Working Stress Design (WSD) and Load and Resistance Factor Design (LRFD) approaches. These formulations are then discussed to get an optimum between simplicity and accuracy of the results.

Progressive Collapse Analysis and Reliability of a Damaged Hull Girder

2014 ◽  
Author(s):  
Achinike U. Ibekwe ◽  
YongChang Pu ◽  
Wan L. Ham ◽  
Robert S. Dow
Keyword(s):  
Ultimate Strength ◽  
Structural Reliability ◽  
Numerical Technique ◽  
Progressive Collapse ◽  
Limit State ◽  
Neutral Axis ◽  
Statistical Characteristics ◽  
Structural Safety ◽  
State Function ◽  
Hull Girder

With the expectation of hull girder asymmetry and corresponding shift in elastic neutral axis resulting from collision damages and other forms of structural deteriorations, the interaction of vertical and horizontal hull girder capacities become quite significant in the assessment of ship structural safety. This paper therefore extends the application of a previously proposed interactive-numerical probabilistic based methodology for structural safety to assess the hull girder ultimate strength reliability of a damaged ship by means of a user-defined numerical framework. Hull girder capacity is calculated using the NS94D ultimate strength code, which is based on the Smith’s progressive collapse method. The resulting deterministic responses have been interactively linked to the NESSUS probabilistic framework so that the reliability of the damaged hull girder is predicted using an implicit limit state function defined based on a transformation of coordinates to appropriately account for any shift in the neutral axis. Random deviations of the constituent variables are directly applied to calculate the ultimate strength deterministic responses, thereby circumventing the need to characterize any correlated strength variable, which is at best subjective. The conventional approach of characterizing ultimate strength by an assumed coefficient of variation and distribution type was found to be conservative in predicting structural safety of ships relative to the proposed method. Application of the interactive-numerical technique for structural reliability is therefore considered significant for problems involving correlated random variables with unknown statistical characteristics. The method is being considered to predict the safety of cracked hull girders by accounting for the residual strength and further load bearing capabilities of deteriorated and adjacent elements.

Analysis Method of Ultimate Strength of Ship Hull Girder Under Combined Loads: Application to an Existing Container Ship

2016 ◽  
Author(s):  
Yoshiteru Tanaka ◽  
Yutaka Hashizume ◽  
Hiroaki Ogawa ◽  
Akira Tatsumi ◽  
Masahiko Fujikubo
Keyword(s):  
Ultimate Strength ◽  
Cross Section ◽  
Bending Strength ◽  
Progressive Collapse ◽  
Fem Analysis ◽  
Ship Hull ◽  
Strength Analysis ◽  
Container Ship ◽  
Hull Girder ◽  
Longitudinal Bending

A ship hull is regarded as a box girder structure consisting of plates and stiffeners. When the ship hull is subjected to excessive longitudinal bending moment, buckling and yielding of plates and stiffeners take place progressively and the ultimate strength of the cross-section is attained. The ultimate longitudinal bending strength is one of the most fundamental strength of a ship hull girder. Finite element method (FEM) analysis using fine-mesh hold models has been increasingly applied to the ultimate longitudinal strength analysis of ship hull girder. However, the cost and elapsed time necessary for FEM analysis including finite element modelling are still large for the design stage. Therefore, the so-called Smith’s method [1] has been widely employed for the progressive collapse analysis of a ship hull girder under bending. Recently, there is a growing demand for a container ship, which is characterized as a hull girder with large open decks. This type of ship has a relatively small torsional stiffness compared to the ships with closed cross-section and the effect of torsion on the ultimate longitudinal strength may be significant. However, the Smith’s method above mentioned cannot consider the influence of torsion. Therefore, some of the authors developed a simplified method of the ultimate strength analysis of a hull girder under torsion as well as bending [2–4]. In this method, a hull girder is modeled by linear beam elements in the longitudinal direction, and the warping as well as bending deformation is included in the formulation. The cross-section of a beam element is divided into plate elements by the same way as the Smith’s method. Therefore, the shift of instantaneous neutral axis and shear center can be automatically considered by introducing the axial degree of freedom as well as the bending ones into the beam elements, and keeping the zero axial load condition. In this study, the average stress-average strain relationship of each element is calculated using the formulae of the Common Structural Rules (CSR) [5] and HULLST proposed by Yao et al. [6, 7] considering the effect of shear stress due to torsion on the yield strength. There had been a lot of papers [8] which discuss the importance of strength assessment to large container ships under torsion. However, there are few papers which discuss the influence of torsion on the ultimate hull girder strength. In this paper, the proposed simplified method is applied to the existing Post-Panamax class container ship. First, a torsional moment is applied to the beam model for the ship within the elastic range. Then, the ultimate bending strength of cross-sections is calculated applying the Smith’s method to a beam element considering the warping and shear stresses. On the other hand, nonlinear explicit FEM are adopted for the progressive collapse analysis of the ship by using LS-DYNA. The effectiveness of present simplified analysis method of ultimate hull girder strength under combined loads is discussed compared with the LS-DYNA analysis.

Reliability Analysis of Ultimate Longitudinal Strength for Ships in Yangtze River

2016 ◽  
Author(s):  
Le Deng ◽  
Ji Guo ◽  
Chuang Fang ◽  
Lu-yao Zou
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Yangtze River ◽  
Bending Moment ◽  
Analysis Method ◽  
Safety Factors ◽  
Hull Girder ◽  
Longitudinal Strength ◽  
Partial Safety Factors ◽  
Wave Induced

With Consideration of the uncertainties of materials yield strength, still water bending moment and wave-induced bending moment, the failure equation is established based on reliability analysis method. The reliabilities of 33 ships navigating in Yangtze River are calculated using improved FOSM method, according to which the target reliability is obtained, and the partial safety factors for hull girder ultimate strength, still water bending moment and wave-induced bending moment are given. As a result the formula for probability assessment of ultimate strength is established. Verification of sample ships shows that the formula is accurate and useful.

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