Ultimate Bearing Capacity Assessment of Hull Girder With Asymmetric Cross-Section

2017 ◽  
Author(s):  
ChenFeng Li ◽  
Peng Fu ◽  
HuiLong Ren ◽  
WeiJun Xu ◽  
C. Guedes Soares
Keyword(s):  
Ultimate Strength ◽  
Cross Section ◽  
Structural Integrity ◽  
Neutral Axis ◽  
Bending Moments ◽  
Hull Girder ◽  
Horizontal Wave ◽  
Asymmetric Load ◽  
Vector Equilibrium ◽  
Error Method

The objective of this study is to investigate the variation of neutral axis of ship hull girder due to asymmetric geometry or asymmetric load, and its influence on the ultimate strength of hull girder. In order to account for asymmetric geometries and loads of hull girders, the force equilibrium and force-vector equilibrium criteria together with a minimum convergence factors (error) method, are employed to determine the translation and rotation of neutral axis plane of symmetric or asymmetric hull cross-section in the application of Smith’s method at each step of curvature of the hull girder. The ultimate strengths of Dow’s 1/3 frigate model with three predefined structural integrity states, one intact and two damaged respectively, are investigated by the improved Smith’s method for a range of variation of heeling angles. The influence of asymmetric geometry and load on the motion of neutral axis plane and on the ultimate strength are analyzed and discussed. The results show that the improved iteration strategy together with the MCFM is self-adapting and more accurate in searching the translation and rotation of neutral axis plane. Finally, the envelope curves of the bending moments in the three predefined integrity states are obtained, which can be used for assessing ultimate strength of hull girders under combined vertical and horizontal wave bending moments.

Ultimate Bearing Capacity Assessment of Hull Girder With Asymmetric Cross Section

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Chenfeng Li ◽  
Peng Fu ◽  
Huilong Ren ◽  
Weijun Xu ◽  
C. Guedes Soares
Keyword(s):  
Cross Section ◽  
Structural Integrity ◽  
Neutral Axis ◽  
Bending Moments ◽  
Hull Girder ◽  
Horizontal Wave ◽  
Asymmetric Load ◽  
Vector Equilibrium ◽  
Error Method ◽  
Force Equilibrium

The objective of this study is to investigate the variation of neutral axis of ship hull girder due to asymmetric geometry or asymmetric load, and its influence on the ultimate strength (ULS) of hull girder. In order to account for asymmetric geometries and loads of hull girders, the force equilibrium and force-vector equilibrium criteria together with a minimum convergence factors (error) method are employed to determine the translation and rotation of neutral axis plane (NAP) of symmetric or asymmetric hull cross section in the application of Smith's method at each step of curvature of the hull girder. The ULSs of Dow's 1/3 frigate model with three predefined structural integrity states, one intact and two damaged, respectively, is investigated by the improved Smith's method (ISM) for a range of variation of heeling angles. The influence of asymmetric geometry and load on the motion of NAP and on the ULS are analyzed and discussed. The results show that the improved iteration strategy together with the minimum convergence factors (error) method is efficient and more accurate in searching the translation and rotation of NAP. Finally, the envelope curves of the bending moments in the three predefined integrity states are obtained, which can be used for assessing ULS of hull girders under combined vertical and horizontal wave bending moments.

A PSO-Based Method for Tracing the Motion of Neutral Axis Plane of Asymmetric Hull Cross-Sections and its Application

2018 ◽  
Author(s):  
Chenfeng Li ◽  
Chao Gao ◽  
Xueqian Zhou ◽  
Sen Dong ◽  
Peng Fu ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
International Association ◽  
Random Search ◽  
Two Dimensions ◽  
Neutral Axis ◽  
Force Vector ◽  
Hull Girder ◽  
Vector Equilibrium ◽  
Force Equilibrium

The Smith’s method is stipulated by the International Association of Classification Societies in the Common Structure Rules as a standard method for estimating ultimate/residual strength of hull girder in both intact and damaged conditions. However, for the latter case where the effective hull cross-section is asymmetric and the neutral axis of damaged cross-section not only translates but also rotates, the additional force vector equilibrium also needs to be applied so as to determine the neutral axis plane. The commonly adopted iterative methods for the two-force-equilibrium problem do not always converge for the desired accuracy. This paper proposes a Particle Swarm Optimization based iteration method to trace the motion of the neutral axis plane of asymmetric cross sections. The translation and rotation of the neutral axis are taken as the two dimensions of particles in the model, and the force equilibrium error and the force vector equilibrium error are the objective functions. The neutral axis is determined by performing a random search within the entire range of possible position of neutral axis. The proposed method has been implemented and validated for the case of the DOW’s 1/3 frigate model, the analysis of efficiency and accuracy shows that the method performs in general better than traditional ones.

Analysis of Thermal Stratification and Fatigue Stress for Pressurizer Surge Line

2010 ◽  
Author(s):  
Xiaofei Yu ◽  
Yixiong Zhang
Keyword(s):  
Cross Section ◽  
Thermal Stratification ◽  
Thermal Stresses ◽  
Structural Integrity ◽  
Bending Moments ◽  
One Dimensional ◽  
Pipe System ◽  
Pipe Cross Section ◽  
Fatigue Stress ◽  
Surge Line

Thermal stratification of pressurizer surge line induced by the inside fluid brings on global bending moments, local thermal stresses, unexpected displacements and support loadings of the pipe system. In order to confirm the structural integrity of pressurizer surge line affected by thermal stratification, this paper theoretically establishes thermal stratified transient and studies the calculation method of thermal stratified stress. A costly three-dimensional computation is simplified into a combined 1D/2D technique. This technique uses a pipe cross-section for computation of local thermal stresses and represents the whole surge line with one-dimensional pipe elements. The 2D pipe cross-section model is used to compute elastic thermal stresses in plane strain condition. Symmetry allows half the cross-section to be considered. The one-dimensional pipe elements model gives the global bending moments including effects of usual thermal expansion and thermal stratification of each model nodes. This combined 1D/2D technique has been developed and implemented to analyze the thermal stratification and fatigue stress of pressurize surge line in this paper, using computer codes SYSTUS and ROCOCO. According to the mechanical analysis results of stratification, the maximum stress and cumulative usage factor are obtained. The stress and fatigue intensity of the surge line tallies with the correlative criterion.

Evaluation of Cumulative Collapse of a LNG Carrier Hull Girder Under Dynamic Cyclic Bending Moments

2021 ◽  
Author(s):  
Jian Ji ◽  
Bin Liu ◽  
Lin Chen ◽  
Xianting Liao ◽  
C. Guedes Soares
Keyword(s):  
Finite Element ◽  
Ultimate Strength ◽  
Failure Modes ◽  
Ship Hull ◽  
Bending Moments ◽  
Nonlinear Finite Element Method ◽  
Cyclic Bending ◽  
Hull Girder ◽  
Hull Structure ◽  
The Difference

Abstract The present paper continues the recent work reported by Liu and Guedes Soares [1] where finite element simulations were conducted to investigate the ultimate strength of a container ship hull girder under cyclic bending moments. Here a membrane LNG carrier is investigated to evaluate the “cyclic ultimate strength” of this specialized ship hull structure including double bottoms, sides and decks. The paper aims to analyze the ultimate strength and to compare the collapse modes of a LNG carrier hull girder under monotonic and dynamic cyclic bending moments, revealing the difference in their failure modes. Nonlinear finite element method is employed, using the explicit LS-DYNA solver, to analyze the ultimate strength of hull structures. The numerical results show that the cyclic ultimate strength of hull structures is about 20% lower than the monotonic ultimate strength in the present study.

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.

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.

Determination of collapse moment of different angled pipe bends with initial geometric imperfection subjected to in-plane bending moments

2021 ◽  
pp. 095440622199640
Author(s):  
Manish Kumar ◽  
Pronab Roy ◽  
Kallol Khan
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Circular Cross Section ◽  
Initial Imperfection ◽  
Bend Angle ◽  
Bending Moments ◽  
Element Analysis ◽  
Geometric Imperfection ◽  
Initial Geometric Imperfection

From the recent literature, it is revealed that pipe bend geometry deviates from the circular cross-section due to pipe bending process for any bend angle, and this deviation in the cross-section is defined as the initial geometric imperfection. This paper focuses on the determination of collapse moment of different angled pipe bends incorporated with initial geometric imperfection subjected to in-plane closing and opening bending moments. The three-dimensional finite element analysis is accounted for geometric as well as material nonlinearities. Python scripting is implemented for modeling the pipe bends with initial geometry imperfection. The twice-elastic-slope method is adopted to determine the collapse moments. From the results, it is observed that initial imperfection has significant impact on the collapse moment of pipe bends. It can be concluded that the effect of initial imperfection decreases with the decrease in bend angle from 150∘ to 45∘. Based on the finite element results, a simple collapse moment equation is proposed to predict the collapse moment for more accurate cross-section of the different angled pipe bends.

Assessment of Residual Ultimate Strength of VLCC According to Damage Extents and Average Compressive Strength of Stiffened Panel

2014 ◽  
Author(s):  
Ji-Myung Nam ◽  
Joonmo Choung ◽  
Se-Yung Park ◽  
Sung-Won Yoon
Keyword(s):  
Compressive Strength ◽  
Ultimate Strength ◽  
Probabilistic Approach ◽  
Stiffened Panel ◽  
Moment Capacity ◽  
Hull Girder ◽  
Damage Area ◽  
Damage Indices ◽  
Smith Method ◽  
Average Compressive Strength

This paper presents the prediction of residual ultimate strength of a very large crude oil carrier considering damage extents due to collision and grounding accidents. In order to determine extents of damage, two types of probabilistic approaches are employed: deterministic approach based on regulations based on ABS [1], DNV [2], and MARPOL [3] and probabilistic approach based on IMO probability density functions (PDFs) (IMO guidelines [4]). Hull girder ultimate strength is calculated using Smith method which is dependent on how much average compressive strength of stiffened panel is accurate. For this reason, this paper uses two different methods to predict average compressive strength of stiffened panel composing hull girder section: CSR formulas and nonlinear FEA. Calculated average compressive strength curves using CSR formulas (IACS [5, 6]) and nonlinear FEA are imported by an in-house software UMADS. Residual ultimate moment capacities are presented for various heeling angles from 0° (sagging) to 180° (hogging) by 15° increments considering possible flooding scenarios. Three regulations and IMO guidelines yield minimum of reduction ratios of hull girder moment capacity (minimum of damage indices) approximately at heeling angles 90° (angle of horizontal moment) and 180° (angle of hogging moment), respectively, because damage area is located farthest from neutral axis.

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