Strength Of Container Ships Research Articles

Parametric study of side collision-induced denting failures on the ultimate strength of a handy-size containership under vertical bending

This study focuses on analysing the collision behaviour and residual ultimate bending strength of a container ship following a collision. Initially, computational models employing nonlinear finite element analysis (NFEA) were used to consider dynamic material parameters like strain rate and crack strain. The accuracy of this numerical approach was verified by comparison with test results. Subsequently, various collision scenarios were analyzed using ABAQUS software, encompassing diverse impact velocities, indenter shapes, and boundary conditions. The aim was to evaluate the reduction in the residual ultimate bending strength of a container ship hull resulting from collisions at both sagging and hogging moments. Finally, empirical equations were formulated to forecast the residual ultimate bending strength based on numerical findings. These equations exhibited excellent accuracy when validated against numerical and experimental data. This methodology and its equations provide valuable tools for assessing the post-collision strength of container ships and enhancing maritime transportation safety.

Estimation of directional wave spectra and hull structural responses based on measured hull data on 14,000 TEU large container ships

To ensure hull structural strength of container ships in association with their increase in size, it is very important to grasp the hull stress histories all over the hull structure in actual sea state. However, ordinary hull stress monitoring systems are insufficient for this purpose because of the small number of stress sensors actually practicable. Therefore, in this paper, we discuss an approach to reproduce the hull stress responses which are not measured based on the estimated wave spectrum from the limited measurement data. To achieve this, we introduce a new model to estimate directional wave spectra based on measured ship stress responses and ship response functions, and further we estimate other ship responses using the model. To model an arbitrarily shaped directional wave distribution, the 360° direction is discretized into 36 directions of 10-degree intervals instead of using a directional distribution function, and in each direction, the wave spectrum is represented using the Ochi (3P) spectrum with three parameters (average wave period, significant wave height, and kurtosis). The authors discuss the evaluation results based on two stress response combinations, and a comparison is made between the sea state estimates made by the proposed method and the ocean wave hindcast database (JWA). Furthermore, by comparing the significant values and the spectra of the measured response of the ship with the estimated response based on both the estimated sea state by the proposed method and the hindcast sea state, the accuracies of the proposed method and the hindcast method are discussed in terms of ship stress estimation at non-instrumented locations.

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads, Part 2: An extension of Smith's method

This paper is the second of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. The nonlinear finite element analysis in Part 1 has shown that local bending deformation of a double bottom due to bottom lateral loads significantly decreases the ultimate hogging strength of container ships. In this Part 2, extending Smith's method for pure bending collapse analysis of a ship's hull girder, a simplified method of progressive collapse analysis of ultimate hogging strength of container ships considering bottom local loads is developed. The double bottom is idealized as a plane grillage and the rest part of the cross section as a prismatic beam. An average stress-average strain relationship of plate/stiffened plate elements employed in Smith's method is transformed into an average stress-average plastic strain relationship, and implemented in the conventional beam finite element as a pseudo strain hardening/softening behaviors. The extended Smith's method is validated through a comparison with nonlinear finite element analysis.

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads part 1: Nonlinear finite element analysis

This paper is the first of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. In the midship part of container ships, upward bottom local loads are usually larger than the downward ones. This leads to the increase of biaxial compression in the outer bottom plating and the reduction of the ultimate hull girder strength in the hogging condition. In this Part 1, the collapse behavior and ultimate strength of container ships under combined hogging moment and bottom local loads are analyzed using nonlinear finite element method. Buckling collapse behavior of bottom stiffened panels during the progressive collapse of a hull girder is closely investigated. It has been found that major factors of the reduction of ultimate hogging strength due to bottom local loads are (1) the increase of the longitudinal compression in the outer bottom and (2) the reduction of the effectiveness of the inner bottom, which is on the tension side of local bending of the double bottom. The obtained results will be utilized in the Part 2 paper to develop a simplified method of progressive collapse analysis of container ships under combined hogging moment and bottom local loads.

Structural Reliability Analysis of Container Ships under Combined Wave and Whipping Loads

A practical methodology for structural reliability assessment of ultra large container ships is proposed in the article. The commonly used limit state function for structural reliability analysis of oil tankers and bulk carriers was extended to take into account the whipping response due to the bow flare slamming. The ultimate vertical bending moment capacity of hull girder was considered as a fundamental safety variable in the limit state function, whereas the stochastic model of the loads consists of static still-water bending moments (SWBMs), low-frequency rigid body vertical wave bending moments and high-frequency whipping bending moments. The stochastic model of SWBM for one of the studied ships was obtained from actual bending moments recorded by the onboard loading computer in 2 years of operation. Linear vertical wave bending moment was calculated by a 3D panel seakeeping code, using International Association of Classification Societies (IACS) recommendation No. 34 for the computation of extreme global wave loads. The nonlinear correction of linear wave bending moment was obtained from the recent IACS Unified Requirement S11A for longitudinal strength of container ships. Impulsive loading was modeled by von Karman added mass variation method, whereas transient dynamic hull girder response was analyzed by Timoshenko beam finite elements. Load combinations between extreme still-water and vertical wave bending moments, and between extreme low- and high-frequency vertical wave bending moments are considered. The structural reliability analysis of two container ships of different sizes was performed using the first-order reliability method, to observe differences in safety levels due to different ship sizes. Safety indices are compared with the International Maritime Organization recommendations for double-hull oil tankers to have credible basis for assessing the obtained results. An extensive sensitivity and parametric study was performed, accounting for various operational, environmental, and modeling uncertainties, as well as for corrosion degradation. The presented study may be useful for classification societies in further development of recently introduced IACS Unified Requirements for longitudinal strength of container ships.

A Study on the Hull Girder Strength of Container Ships with Large Hatch Openings

This paper presents the investigated resuts of numerical simulation pertaining to the hull girder strength of container ships in irregular sea.Using the so-called total system of hull girder strength analysis developed by the authors, the analysis of the long-term prediction of structural response of three container ships is carried out.And the wave-induced stresses in longitudinal strength members, distortion of hatch openings and the torsional deformation of hull girder are studied from the point of view of the long-term prediction.As a result of this simulation, the following conclusions are obtained.(1) In the middle part of ship, the wave-induced normal stress in the upper deck at the side edge of hatch opening is in the stress range of 89.5kg/mm2 and the wave-induced shearing stress in the outer hull at the load water line is below 10kg/mm2 with probability level 10-6.The normal stress of outer hull at the bilge part is in the same level with that of the upper deck.(2) In the fore hold structure, the normal stress of the upper deck is almost in the same level with that of the middle part of ship.Furthermore the torsional deformation of hull girder is considerably large compared with that of the middle part of hull because of the decrease in the torsional rigidities.(3) As to the distortion of hatch openings, the elongation Δl of the diagonal length of them is largest in the hatch of the middle part, but there are small differences in the ratio Δl/l with same probability level.

On the transverse strength of ships with large deck openings

A theoretical technique is outlined upon which the strength of container ships, and other vessels with large deck openings, might be based. Such ships require special consideration because the warping of cross sections cannot be neglected when they suffer antisymmetric distortions. In the development of the theory, a number of new results are given relating to antisymmetric vibration of a thin-walled beam of open section; these relate to the modes and to the orthogonality conditions that they satisfy. It is demonstrated that analysis of transverse strength in waves can be made to provide the information that is normally sought in inde­pendent studies of ‘seakeeping’.

Numerical simulation in torsional strength of container ships with large hatch openings

In numerical simulation pertaining to torsional strength of large container ships, various problems encountered in the initial stages of designing ships with large hatch openings are discussed.An actual ship of 38, 000 gross tonnage (container capacity : 1, 800 of 20' container) is adopted as the type ship, and the loading condition is based on the method proposed by Wilde.In the analysis, ships are treated as beam shells with variable cross-section, and a coupling effect between torsion and horizontal bending is also taken into account.As a result of this simulation, the following conclusions were obtained.(1) It was found that the most severe condition possibly occurs not in the middle part of ship but in the part about L/4 (L : ship length) apart from the bow.So the effect of variable cross-section should not be neglected in the analysis.(2) The effect of the double hull structure of ship side is considerably large to increase the torsional strength of container ships.(3) The application of the high tensile steel to the upper deck part gives little effect on the increase of torsional deformation in spite of the decrease of the plate thickness of that part.(4) In arranging the cross decks between hatch openings, provision of a large member in the middle part between the midship and the bow is very effective for the torsional strength.(5) The tier type structure is preferable to the knuckle type in various respect. In particular this type will assure a greater strength in the section toward the bow.

On a Study of the Longitudinal Strength of Ships with Torsional and Horizontal Deformations

In addition to the longitudinal bending and shear deformation of ships in the vertical plane, the effect of longitudinal bending and shear deformation of ships in the horizontal plane coupled with the torsional deformation is particularly considered in the method of theoretical analysis.This theoretical analysis treats the ship as a beam shell with various cross-section in which the actual structure of ship is rather faithfully considered.Concerning the structural idealization, ships are divided into substructures with uniform cross-section and then each substructure is also divided into small strip elements.Further, the experimental works are carried out, using a model of container ship with large hatch openings. And it has been confirmed that the calculated results obtained through this method are in good agreement with the experimental results.The results of this investigations led to the following conclusions.In dealing the longitudinal strength of container ships considering the horizontal bending and torsion, the analytical method described here seems to be effective for the practical use in designing of ships.In the structural analysis of container ships, the cross decks between hatch openings should be treated as a reinforced member arresting the torsional deformation of main hull instead of treating them as a part of it. And it is appropriate to adopt 1.0 as the fixedness of the end connection of cross decks for the practical use in the calculating the torsional strength of the main hull.

Design Consideration on Transverse Strength of Container Ships

In our previous papers, the torsional strength and rigidity of container ship are reported, but in this paper described is the transverse strength of hull being one of the serious problems of container ship with long and wide hatch opening.To examine the transverse strength, the double bottom and side structure were substituted to plane structure and analyzed by using computer.Summary results were obtained as follows.1) The ballast condition is the severest among of several loading conditions.2) Where the double hull changes to the single hull in the middle of the hold, the stress is the higher in the vicinity of this area.3) When a deep floor equal to the height of a container was fitted, the shear force of the floor and the bending moment of the center girder decreased by about 20 and 10 percent, respectively.4) The value of the mutual friction between containers and between a container and the ship's bottom has no direct effect on the stress of the floor and the girders that were being considered here.5) The shear force on the double hull part and the axial stress on the transverse box girder were not so large to cause problem.

Design consideration on torsional strength of container ships

The first container fleet in Japan is coming into view as a part of containalization of this country. This paper gives the result of our study on the torsional strength and rigidity which is the most serious problem in the structural design of container ship.First, the twisting moment acting on hull was obtained in static and the values of moment were compared with those by De Wilde's or Vedeler's theory.Second, distortion of hatch opening and nominal bending and shear stress acting on the ends of cross deck in actual ship were studied and the effect of reinforcement at cross deck, was investigated.