Strength Of Ship Research Articles

Residual ultimate strength of ship cracked plates considering fatigue crack propagation under cyclic loads

ABSTRACT The main objective of this paper is to investigate the bearing capacity behaviour of cracked plates considering low-cycle fatigue (LCF) propagation under cyclic loads. The accumulative plastic damage after crack growth is treated as the residual stress and deformation of the plate. In this study, a cracked plate model is proposed to investigate the difference of its residual ultimate strength with preset crack and LCF crack. The present study has analysed the relationship between accumulated lateral deflection and residual stress of cracked plates in different cases. Its effect on the collapse behaviour of the cracked plate is also discussed. The influence factors such as crack length, tensile /compressive cyclic loads, maximum load, minimum load and crack location type are considered in the ultimate strength study of cracked plates. The numerical results clearly reveal the accumulative plastic damage and the bearing capacity behaviour of cracked plates under different cyclic loads.

Making sense of speed effects on ice crushing pressure-area relationships in IACS ice-strengthening rules for ships

Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the understanding of ice loads on larger ships are needed to achieve a better structural design with reduced steel weight. Published rules for the strength of ships are derived from semi-empirical methods and calibrated with limited full-scale measurements on small ships. In 2015, the Lloyd's Register pointed out that for independent navigation of larger ships in heavier ice conditions, steel weight increases exponentially with the ice thickness, which negatively affects the economy of ships' operations.Motivated by this statement, the objective of this paper is to address uncertainty in rule-derived ice loads using an ice mechanics point of view. The focus is on the local ice crushing loads and the vessel speeds in the Unified Requirements for Polar Class Ships of the International Association of Classification Societies (IACS).In this work, we attempt to relate the IACS speed-dependent ice pressure-area relationships to the simplified principles of ice mechanics coupled with structural design considerations. This relation enables us to better understand uncertainties in the rule loads for larger ships, which is essential to address the economy of Arctic ships’ operations. The results of this study showed that the choice of parameters in IACS ice crushing loads for larger vessels with higher ice classes (PC1) has high uncertainty and the upper limit values are greater than those predicted by the ice mechanics approach.

A probabilistic approach to assess the computational uncertainty of ultimate strength of hull girders

The simplified progressive collapse method is codified in the IACS Common Structural Rules (CSR) to calculate the ultimate strength of ship hull girders in longitudinal bending. Several benchmark studies have demonstrated the uncertainty of this method, which is primarily attributed to the variation in the load-shortening curve (LSC) of local structural components adopted by different participants. Quantifying this computational uncertainty will allow the model error factor applied for the ultimate strength of hull girder in a reliability-based ship structural design to be determined. A probabilistic approach is proposed in this paper to evaluate the prediction uncertainty of ultimate strength of the hull girder caused by the critical characteristics within the LSCs. The probability distributions of critical load-shortening characteristics of stiffened panels are developed based on a dataset generated by empirical formulae and the nonlinear finite element method. An adaptable LSC formulation, with the ability to cater for specific response features of local components, is utilised in conjunction with the Monte-Carlo simulation procedure and the simplified progressive collapse method to calculate the ultimate strength of a hull girder at each sampling. The proposed method is applied to four merchant ships and four naval vessels. The computational uncertainties of the ultimate strength of the case study vessels are discussed in association with their mean values and standard deviations. The study shows that the ultimate strength of ship hull girders is subjected to different uncertainties in sagging and hogging. Whist the strength of merchant ships are primarily governed by the ultimate compressive strength of critical stiffened panels, the strength of naval vessels are also sensitive to the post-collapse response of critical members.

Probability of Sea Condition for Ship Strength, Stability, and Motion Studies

Modeling and simulation continues to be an important tool for determining the response of sea-going vessels to wind and waves. To provide appropriate forcing functions to the models, it is important to have environmental data of sufficient fidelity to facilitate an assessment of platform response, which is as accurate as possible within the practical constraints of time and resources. Fortunately, there are a variety of sources of good wave data, including the U.S. National Oceanic and Atmospheric Administration. This study examines the wave data in the context of simulation codes for assessing characteristics of ocean craft response. It also looks at some practical considerations to limit the scope of simulations. The work is strongly influenced by modeling and simulation of naval surface ships, looking for extreme behaviors, but many of the issues discussed are broadly applicable to other applications. Copyright 2021 Her Majesty the Queen in Right of Canada, Department of National Defence

Study on the strength of a fishing boat made from plastic recycles

Ship’s strength is a very significant factor in ship design. In this research, a study of the strength of ships made of recycled plastic material has been carried out. The ship has been designed according to the needs of the load weight, passengers, propulsion system, fishing equipment and the weight of the material itself. Then the load is distributed into the design, where the profile shape and plate thickness used are assumed to be temporary. The strength of the boat analysed, and the minimum plate thickness required in the design is 10 mm with maximum strain The recycle plastic used is type 2 (HDPE).

Bending moment analysis of super large ore carrier based on graphical interface development

In order to improve the safety of shipping process, this paper designs a graphical user interface for calculating the static water bending moment of super large ore earner. Due to the complexity of the actual loading conditions, the long hull girder and the mobility and sinking of cargo, the irregular distribution of gravity and buoyancy along the direction of the captain of the VLCC is prominent. In the actual loading process of ships, compartment loading is adopted in many cases, and the position where the maximum shear force and bending moment appear is generally not in the corresponding position. Traditional ship strength analysis methods can be divided into two kinds. One is to establish the ship’s finite element model to calculate the ship’s strength. The other is to calculate the ship’s strength according to the simple beam bending theory. In this paper, a 360m VALE MAX ore carrier is taken as an example to calculate the local bending moment of the ship at a specific position by using QT software. Compared with the ship loading manual, the error of the program is small, and the program has guiding significance in the actual shipping process.

Numerical and Experimental Investigation on Nonlinear Cyclic Collapse Response of Ship Model in Regular Waves

Abstract Large ocean waves with large wave height may destroy the ship’s structure, whereas it is difficult to predict the nonlinear dynamic strength in the large waves. In this study, we used a nonlinear simulation based on boundary element method (BEM)-finite element method (FEM) and a collapse experiment of ship model to study dynamic ultimate strength and dynamic course of collapse of ship structure, the collapse test was performed in regular tank wave. Besides, a simulation method for nonlinear dynamic ship strength was proposed to predict and compare the results of collapse test. A collapsed model consisting of a plastic hinge and two ship strips is designed. Subsequently, we performed the nonlinear simulation of the ultimate strength of ship model induced by tank wave. Wave loads were calculated following potential theory and BEM. Next, ship structural FEM model was modeled, the ship pressure was transferred to ship wet surface elements, and inertia force was exerted as well. Finally, the nonlinear dynamic strength calculation of ship model was performed in accordance with nonlinear FEM. A four-point-bending test adopted displacement controlling method was designed to obtain the hysteresis characteristic of the elastoplastic hinge. Hysteretic test and simulation analysis was performed to determine post-ultimate bending moment. Time-domain computational results including rotation angle history and vertical bending moment are close to collapse test results so that the two methods are verified. This study verifies that structural nonlinearities of ship structure induced by wave loads could be predicted.

Progressive Collapse Analysis of Intact and Damaged Ships under Unsymmetrical Bending

This study examined the hull girder strength of intact and damaged ships by adopting the incremental-iterative method for progressive collapse analysis, which was extended to the general case of the unsymmetrical bending of beams with an arbitrary cross-section. The sources of an unsymmetrical loading, including rotation of the loading plane and section asymmetry caused by structural damage, are described. A fast and robust procedure is presented to determine the translation and rotation of the instantaneous neutral axis at each curvature increment when applying Smith’s progressive collapse analysis method. A series of analyses were conducted on a double hull VLCC and a bulk carrier, considering various loading plane angles and damage conditions. The decrease in ultimate strength and the influences of rotation of the instantaneous neutral axis and ship heeling are discussed. The proposed method can be used for a rapid and rational assessment of the hull girder strength under adverse conditions.

Influence of corrosive wear on hull strength of sea-going ships

Object and purpose of research. This paper discusses hulls of ships, both in-service and under construction. The purpose of the research is to evaluate and monitor the effect of corrosion wear on their global and local strength.
 Materials and methods. Corrosion wear was taken into account on the basis of the methodology of the Rules of the Russian Maritime Register of Shipping and service life test data for hull samples. The assessment of the corrosive wear effect on the local strength of the plates was carried out using the finite element method.
 Main results. The corrosive wear effect on the parameters of global and local strength of ship hulls is considered. Experimental fatigue curves are obtained from service-life test results for welded samples with and without corrosive wear. Numerical modeling of the change in the stress-strain state of the plate on the size and number of corrosion pits is performed. Various methods of accounting for corrosive wear in the rules of international and indigenous classification societies are considered.
 Conclusion. The obtained results demonstrate and confirm the need to take into account corrosive wear when calculating the overall and local strength of new and used ship hulls.

Structural Degradation of Oil Tanker Operating in Indonesian Waterways

Corrosion is one of the significant factors for decreasing strength in floating marine structures. In general, rules of classification society use the North Atlantic Ocean located in the sub-tropical region as a reference area in the formulation of the structural strength. If the sub-tropical area compare with tropical region such as Indonesia waterway, Indonesia waterway has high salinity and humidity. This makes marine environment in Indonesia more corrosive. One example of the effects of corrosion is the reduction in plate thickness. This leads to decrease in ship strength. Using measured thickness data collected from 25-thickness measurement reports from 24 Oil Tankers that sailing in Indonesian waterways, the diminution of ship structural thickness has been analysed. The age of Oil Tankers, whose data was taken, ranges from 5 to 23 years. Data analysis was carried out by using statistical approach based on Weibull distribution. Using 95% cumulative probability, it was found that the thickness diminution of Oil Tanker with design life of 20 years is 2,07 mm for deck plate, the side plate is 2,06 mm, the bottom plate is 1,81 mm and the inner bottom plate is 1,53 mm.

Investigating the effect of brittle crack propagation on the strength of ship structures by using peridynamics

Ship structures can experience damages although they are initially designed with high safety factors. These damages can be caused by many reasons such as collisions, groundings, explosions, corrosion, fatigue, overloading or extreme conditions. Brittle damages can occur on the ship structures in some special conditions such as low-temperature, high-loading rate, multi-axial stress constraint, or low weldability of steel. In this study, progressive brittle damages on a ship structure subjected to different loading conditions are predicted. A novel peridynamic method based on a recently developed peridynamic shell model is presented to evaluate the structural strength during the damage evolution process for the first time in the literature. First, longitudinal strength (bending moment) of a ship structure is numerically calculated during damage propagations. The maximum longitudinal strength of the intact ship is verified with the experimental result. Next, the simulations are further extended to investigate the ship structure with initial damage, i.e. rectangular cut-out at the bottom. The longitudinal strength for an intact ship and a ship with different sizes of cut-outs are also compared. Finally, torsional strength during the damage propagation process for a ship structure with a cut-out is also presented.

Investigations on the ship-ice impact: Part 1. Experimental methodologies

In the structural design of the Polar Class ships, glancing impact with ice has been considered as the governing load scenario for dimensioning the bow structure. At present, non-linear transient dynamic analysis has been reckoned as a fundamental requirement in the assessment of the structural strength of ships with higher ice classes. Under such requirement, understanding of the dynamic characteristics of the ship-ice impact load appears significant importance. The present study aims to investigate the spatial and temporal variations of the impact loads by simulating the glancing impact events between a polar research vessel and giant ice floes in ice tank. The ship-ice impact loads were recorded by a grid-based tactile sensor attached on the bow area of the model ship. To achieve a reasonable simulation on the design scenario described by the IACS Unified Requirements for Polar Class Ships (UR I), a series of methodological calibration tests were preliminarily carried out to determine the key parameters that should be carefully monitored and controlled, accompanying with thorough discussions on the ship-ice impact process. This paper provides detailed information on the preliminary methodological calibrations and the tactile data processing techniques, including the identification of the ship-ice contact area, the depiction of the ice loading trail and the outline of the spatial distributions of local ice pressures. A companion paper provides detailed analyses and discussions regarding the spatial and temporal variation of the ice impact loads from the formal tests based on the proposed testing procedures obtained by the methodological calibrations.

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.

Effect of low temperature on fatigue crack propagation rates of DH36 steel and its butt weld

As common marine steel for polar ships, the fatigue crack propagation rates of DH36 steel at low temperature have a crucial influence on the evaluation of the fatigue strength of polar ships. The purpose of this paper is to study the fatigue crack propagation rates of DH36 steel with the different scenarios between the conventional base metal and butt weld specimens at room temperature (RT) and −60 °C. The fatigue crack propagation test and Vickers hardness test of butt weld and base metal were performed. As a result, the fatigue crack propagation test demonstrated a reduced crack propagation rate in both the base metal and the butt weld with a decreasing ambient temperature. For the Vickers hardness, both the welded joint and the base metal at −60 °C presents higher hardness values than RT. Furthermore, the welded joint trends to demonstrates a higher value of Vickers hardness than base metal. Finally, the behavior of fatigue crack propagation in the micro scale between base metal and butt weld at low temperature was described by the fractography.

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.

Ultimate Strength Investigation of Ro-Ro Ship

Ro-Ro ship has special characteristic for cargo handling because the cargo is transferred in horizontal direction. For example, cars can move by using ramp door which is located in front and/or aft of the ship. In conjunction with this, car passenger and other decks such as top including bottom part need to be investigated for local and global of Ro-Ro ship structure. In the present study, the ultimate strength investigation of Ro-Ro ship is conducted. There are three types of Ro-Ro ships are taken as the ship’s subject. The cross section of Ro-Ro is considered in the analysis and it is modelled having plate and stiffened plate. The one-frame is represented in longitudinal direction. The simply supported of boundary condition is applied and the cross section is assumed to be remained plane. The calculation of the ultimate strength using in-house integrated program. The ultimate strength of Ro-Ro ship is investigated under hogging and sagging conditions. The vertical bending moment is imposed to the cross section to obtain the ultimate strength including their progressive collapse. The result obtained by in-house program for three types of Ro-Ro ships are summarized and the collapse behaviour for local and global of the decks to the ultimate strength of Ro-Ro ship are also presented in this study.

Study on Transverse Strength of the Deck-Container Ships due to Laying All Containers on Deck

The strength of transversal structure of the ship has a great effect on the safety of ship. Shipswill experience conditions that affect the strength of the ships structure. A deck-container ships are the ships that all container are loaded on deck such as MV. Khendaga Nusantara series ships. The transversal strength of the ships is loaded mainly by the weight of cargolaying on deck.. This research aims to determine the transverse strength of a deck-container ship due to the all container loads on deck. The research was done by usingfinite element method throughmodeling transverse ship structure, the simulation is conducted by varying the amount and lay-out of containers on dec). The loads appliedto the model are side loads, bottomloads, and deck loads in according to BKI rules. The results shows that the stress that occurred in the web frame was 140,63 N/mm2due to the placement of the entire container on the deck(full loading). For ship structure response, a deformation of 2,86 mm occurred in the web frame area at maximum loading. Stress ratio that occurs in all ship’s structuredoes not exceed 1 in other words the working stress does not exceed the allowedstress according to BKI rules.

Numerical Investigation on Ultimate Compressive Strength of Welded Stiffened Plates Built by Steel Grades of S235–S390

The welded stiffened plate is widely used in naval architecture and offshore engineering as a basic structural member. The aim of this study is to investigate the effect of welding residual stress and steel grade on the ultimate strength of stiffened plates under uniaxial compressive load by non-linear finite element analysis. Nineteen stiffened plates built with three types of stiffeners with various column slenderness ratios provided in the ISSC’2000 VI.2 benchmark calculations are employed in the present study. The commercial finite element code ABAQUS is applied to simulate the collapse behavior of the stiffened plates and verified against the benchmark calculations. Fabrication-related imperfections, such as initial deflections and residual stresses, are accounted for in the simulations. The ultimate strength of stiffened plates built in common shipbuilding steels, namely S235, S315, S355 and S390, are investigated by varying the yield strength of materials in the simulation. Analysis of the numerical results shows that the welding residual stress reduces the ultimate strength of stiffened plates, and increase in yield strength of the material can effectively improve the ultimate strength of common ship stiffened plates; and quantitative analyses of their influences have also been performed.

Impact analysis in an engineering environment

ABSTRACTAssessment of the residual strength of ships after accidental loads has gained importance. Only if the load-carrying capacity after possible accidents is known, the structural safety can be judged. Analyses of accidental impacts and residual strength have been mainly performed with dedicated codes. Improved general purpose analysis software packages make it worthwhile to assess engineering environments to perform such analyses. Drop tests are simulated within the ANSYS Workbench to assess the analysis of accidental impacts. The results are compared to mesh size dependent criteria in the literature. The influence of geometry, material plasticity models and modelling techniques is investigated. Possibilities to transfer the results to further analyses of residual strength are discussed. In conclusion, a comparison of modelling methods is presented for more accurate results and higher time efficiency in non-linear dynamic analyses under impact loads. The applicability of further analyses to the deformed structures is given for future work.

Ultimate Longitudinal Strength of Ships' Hull Girder under Combined Loading — 3rd Report: Introduction of the effect of bulkheads and side structures to torsional analysis with using 1 dimensional finite element method —

In recent years, container ships become larger and larger to increase the transport efficiency. The torsional rigidity of a container ship is lower than other type of ships, because the container ship has the large deck opening and large flare structure. Therefore, it is important to calculate the longitudinal ultimate strength with considering the torsional moment for the design of ships.