Ship Side Structures Research Articles

An analytical method for predicting the structural response of ship side structures by bulbous bow in oblique collision scenarios

ABSTRACT As more and more ships sail on the sea, the probability of collision between ships also increases. At present, researches more on head-on ship collisions than oblique ship collisions. According to statistical data, the probability of oblique ship collision is higher than that of head-on ship collision, and oblique ship collision may cause a wider range of structural damage. Therefore, this paper studies the damage deformation of ship side structures in oblique collision scenarios. In this paper, a simplified analysis method is proposed to predict the structural response of the struck ship’s side structures by bulbous bow in oblique collision scenarios and the analytical results match well with the numerical simulation results, which verifies the accuracy of the simplified analysis method. The simplified analysis method can be used to assess the crashworthiness of ship side structures by bulbous bow in oblique collision scenarios.

Numerical simulation on Crashworthiness of 105000t LNG Carrier

It is of great significance to study the crashworthiness of LNG carrier to improve its crashresistance and enhance its operation safety. In this paper, the collision process between the bulbous bow of the container ship and the side structure of the LNG ship is analyzed by using nonlinear finite element numerical simulation. Collision performance of LNG carrier and collision indicators during the collision, the impact force, velocity and displacement and energy absorption in the process of collision by changing parameters of the major velocity, impact angle and impact location and others are studied. The relevant research results have a strong practical significance for analyzing the deformation, strengthening measures and structural repair of ship side structure impact damage.

An analytical method to assess the structural responses of ship side structures by raked bow under oblique collision scenarios

With the development of the shipping industry, the number of ships at sea has increased significantly. According to the statistical data, oblique ship collisions are much more frequently happened than that of head-on ship collisions. However, there are less researches on oblique ship collisions than those of head-on ship collisions. The responses of hull structure during oblique collision scenarios are different from those in head-on collision scenarios, and might have wider structural damages, which demonstrate the significance of research on oblique collision scenarios and structural damage. In this paper, the oblique collision scenarios are firstly investigated through numerical simulations. Finite element software LS_DYNA is used for the numerical simulations. Six typical oblique collision scenarios are defined, on purpose of finding the main deformation characteristics of the struck ship. Two basic assumptions were made accordingly. Then, a simplified analytical method is proposed to predict the structural response of ship side structures by raked bow under oblique collision scenarios. The new analytical method includes the deformation mechanism of the side plating, the web girder and the transverse frame. The resistance and energy dissipation of these components are used in an integrated way to evaluate the overall crashworthiness of the side structure of the struck ship. The numerical simulation results match well with the results of analytical calculations, which validates the accuracy of the proposed analytical method. The proposed analytical method can provide an effective way to evaluate the structural crashworthiness of ship side structures in oblique collision scenarios during the structural design stage.

Study on Striking Ship with Loading Impact on the Performance of the Double Hull Oil Tanker Collision

Abstract Due to the great danger of the collision of oil tankers, lots of research on the collision of oil tankers has been carried out. But, at present, the research on the collision of oil tankers mainly focuses on the loading condition of the struck ship, ignores the impact on the loading condition of the striking ship. However, during the actual oil tanker collision, the striking ship is generally in the state of loading. Therefore, it is necessary to carry out the analysis of the impact of the loading condition of the striking ship on the collision damage of the oil tanker. In this paper, the effect of striking ship with loading on the impact performance of the side structure during the collision of the cargo double hull oil tanker has been investigated. The ship collision model was established by using the finite element software ANSYS/LS-DYNA which is based on 7000 tons of double hull oil tankers. Based on the analysis of the collision force, impact of striking speed changes, impact of striking deep changes and structural energy absorption during the collision process, the influence of the striking ship with loading on the damage mechanism and the impact performance of the double shell oil ship side structure was expounded. The results show that the influence of the striking ship with loading can be great to the damage to side hull during the research of the collision performance of the oil tanker.

Effects of a deformable striking ship's bow on the structural crashworthiness in ship–ship collisions

ABSTRACTShip–ship collision accidents continue to occur regardless of the continuous efforts to prevent them, and they essentially involve highly nonlinear problems associated with structural crashworthiness due to crushing and fracture. The nonlinear finite-element method is one of the most powerful techniques to solve the problems. In industry practice, the bow structure of a striking ship is often modelled as a rigid body as it is usually much stiffer than the side structure of a struck ship. However, reality is that the initial kinetic energy in a ship–ship collision accident can be absorbed by the damages of not only the struck ship's side structures but also the striking ship's bow structures because the striking ship bow structure is actually deformable. The aim of the present study is to examine the effects of a deformable striking ship's bow on the structural crashworthiness in ship–ship collisions. In the present study, two scenarios are considered where the side structure of a VLCC class double hull oil tanker is collided by the bow structure of a VLCC class double hull oil tanker or a SUEZMAX class double hull oil tanker. All of the ships considered are real ships in operation. The structural crashworthiness in terms of the collision force–penetration relation and the collision energy–penetration relation is then studied with two cases in which the striking ship's bow structures are either rigid or deformable. It is concluded that the striking ship's bow may be modelled as a rigid body in minor collisions at a collision angle of about 90° where the initial kinetic energy is entirely consumed before the inner hull structure is ruptured, but it should be modelled as a deformable body in a major collision accident or at an inclined collision angle where the maximum penetration can be greater than the double side breadth.

Load carrying capacity of ice-strengthened frames under idealized ice load and boundary conditions

Overload response of the stiffening frames in ship side structure due to ice loading is an important design consideration for ships operating in ice infested waters. By overload, we mean loads that are larger than assumed by the rules. Therefore, the response of ice strengthened grillage frames is investigated under a range of idealized rectangular pressure patches and by assuming different boundary conditions for the structural units. A flat, representative grillage of an ice-strengthened ship is considered and analysed using non-linear Finite Element Method. The response of the grillage frames is compared with the isolated frame response. Two frame types are considered: flatbars and L-frames. Finite element simulations revealed that patch length has strong effect on the frame deformation mode. The key characteristic that differentiates the response under shorter and longer patches is the longitudinal membrane stretching of the shell plating. Longer patches tend to suppress this deformation mode that leads to similar frame behaviour observed in isolated frame analysis. It is further shown that overload capacity of grillage frames reduces with increasing patch length to levels observed in isolated frame analysis. Analysis of plastic strain development in the frames and plating revealed that plastic strain localized faster in frames, but shell plating is more sensitive to patch height variations. This renders frames more susceptible to fracture than plating. Finally, the local failure mechanisms of the L-frames tend to diminish the load sharing capability and so negatively affects the overload behaviour.

Study on Collision of Ship Side Structure by Simplified Plastic Analysis Method

During its lifetime, a ship may encounter collision or grounding and sustain permanent damage after these types of accidents. Crashworthiness has been based on two kinds of main methods: simplified plastic analysis and numerical simulation. A simplified plastic analysis method is presented in this paper. Numerical methods using the non-linear finite-element software LS-DYNA are conducted to validate the method. The results show that, as for the accuracy of calculation results, the simplified plasticity analysis are in good agreement with the finite element simulation, which reveals that the simplified plasticity analysis method can quickly and accurately estimate the crashworthiness of the side structure during the collision process and can be used as a reliable risk assessment method.

A Rubber Bag for Liquid Cargo to Improve Ship Collision Resistance

Collisions and grounding accidents of ships, but also the failure of the hull-integrity, can lead to oil leakage. Examples are the Rena in 2011, the Hebei Spirit in 2007, and the much known accident of the Prestige in 2002. Consequently, research regarding the enhancement of the structural design to increase the safety-level of ships in case of accidents is important. In this paper, the use of a rubber bag as a second barrier is presented as an alternative concept to prevent oil leakage in case of accidents. The influence of the rubber bag is investigated using the exemplary simulation of a ship collision. A simplified tanker side structure as well as a box-shaped rubber bag is analyzed with the finite element (FE) method. The material model for the rubber bag is calibrated with tensile tests to obtain the required material parameters. The reaction forces and the associated penetration depth are analyzed. The comparison is done between the structure with and without the rubber bag. For the latter, the general behavior of an empty tank in a ship side structure is compared with the large-scale experimental results. Furthermore, an additional increase of the collision resistance of the ship due to the rubber bag without changing the common structural design is discussed.

An analytical method for predicting the ship side structure response in raked bow collisions

As an increasing number of ships continue to sail in heavy traffic lanes, the possibility of collision between ships has become progressively higher. Therefore, it is of great importance to rapidly and accurately analyse the response and consequences of a ship's side structure subjected to large impact loads, such as collisions from supply vessels or merchant vessels. As the raked bow is a common design that has a high possibility of impacting a ship side structure, this study proposes an analytical method based on plastic mechanism equations for the rapid prediction of the response of a ship's side structure subjected to raked bow collisions. The new method includes deformation mechanisms of the side shell plating and the stiffeners attached. The deformation mechanisms of deck plating, longitudinal girders and transverse frames are also analysed. The resistance and energy dissipation of the side structure are obtained from individual components and then integrated to assess the complete crashworthiness of the side structure of the struck ship. The analytical prediction method is verified by numerical simulation. Three typical collision scenarios are defined in the numerical simulation using the code LS_DYNA, and the results obtained by the proposed analytical method and those of the numerical simulation are compared. The results correspond well, suggesting that the proposed analytical method can improve ship crashworthiness during the design phase.

Granulate material for structural design: a concept to strengthen ship side structures

Granulate material for structural design: a concept to strengthen ship side structures

Characteristics of material, ship side structure response and ship survivability in ship collisions

Research on ship collision and grounding has taken giant steps during the last decade. One reason is that computer capacity has increased and, therefore, also the possibility to simulate various collision scenarios in a realistic way using more advanced and larger models. As a result, it has been possible to investigate in more detail the understanding of structural integrity, characteristics and failure phenomena that interact during, for example, a collision. This article summarises research experiences from a research group that has been working with ship collision safety, using both experiments and numerical simulations by finite element (FE) analysis. Results are presented from tensile and forming limit tests, followed by FE analyses of these with the objective of predicting material rupture using appropriate constitutive material models and damage criteria. An example of an innovative design of a side-shell structure that is considered to be more intrusion-tolerant than most side-shell structures used today is demonstrated. Finally, results from a research project which has a holistic approach on the assessment of survivability of a struck ship are presented. In the project, a methodology has been developed which combines structural analysis and damage stability analysis followed by risk analysis.

A procedure to optimize ship side structures for crashworthiness

This paper presents a procedure to optimize a conceptual ship side structure from a crashworthiness point of view. As an example, this procedure is presented for a chemical or product tanker. A particle swarm optimization algorithm is used for the procedure. The classification society compliance of the conceptual design is checked through service loads that are applied to the ship's hull girder according to Det Norske Veritas. The collision simulations to assess the crashworthiness are carried out with the non-linear finite element solver LS-DYNA. An element length-dependent constant-strain failure criterion is chosen to simulate rupture. A numerical simulation of a stiffened plate serves to validate the material relation until failure. This material relation and failure definition makes possible an accurate prediction of the structural energy absorbed until inner plate rupture. The procedure is adjustable and applicable to other ship types and scenarios.

Simulating the collision response of ship side structures: A failure criteria benchmark study

Simulations of the collision response of three different ship side structures are performed using the finite element method. The aim is to obtain a force-penetration curve based on the inner mechanics without considering outer dynamics. Respective structures were previously tested in large scale under the right angle ship-ship collision with a bulbous bow and these experiments were used to validate the simulations. The analysis focus is to determine the influence on the collision results from different failure criteria including the mesh size sensitivity. This paper applies the Germanischer Lloyd (GL) criterion based on thru thickness plastic strain, the criterion based on studies of Peschmann and the Rice-Tracey and Crockcroft-Latham (RTCL) criterion. The comparison of results attained here with the experimental results brings an insight into the sensitivity of the failure criteria. The final conclusion of this work is the performance of the studied failure criteria and further guidelines for collision or grounding simulations.

On deformation and perforation of ship structures under ballistic impacts

This paper investigates the characteristics of the deformation and perforation on thin-walled structures under ballistic impacts based on the DYNA3D numerical simulations. Perforation mechanisms of plates and numerical modelling techniques to simulate the response of thin-walled structures under ballistic impacts are discussed to some extent. A benchmark study on deformation and perforation of steel plates struck by a rigid projectile is made by a comparison with DYNA3D simulations and existing experimental results where available. Perforation behaviour of a naval shipside structure impacted by a cannon ball is simulated by DYNA3D. By the regression analysis of the present DYNA3D computations and some existing test data, a new empirical formula that relates impact energy absorbed up to perforation of the target plate with the impact velocity of the projectile is developed. The developed formula can cover a wider range of the impact velocity up to 800 m/s, while existing formulae are valid up to 120 m/s. It is concluded that the technology developed from the present study will be useful for design and hazard assessment of thin-walled structures to avoid the perforation by ballistic impacts.

Strength Estimation Method of Ship Side Structures Subjected to Hard Bow Collision

In the collision of hard and sharp bows breaking of ship side structures starts from the collided point of bow, while in the collision of soft and rounded bows breaking is likely to start from the supported point such as bulkhead or transverse web frame. In the case of breaking from collided point stretching of ship side structures is followed by crack propagation, so absorbed energy should be evaluated in consideration of crack propagation.In this paper to develop an evaluation method for breaking from collided point, double hull panel models, which are typical as ship side structures of VLCC, were destructed with the indentation of rigid bow model which was pushed dynamically as well as statically. In the first crack initiation condition was investigated by FEM simulation using fine mesh solid element models and crack initiation was found to be estimated with the ductile damage parameter which consists of equivalent plastic strain and stress triaxiality. Then crack propagation condition was investigated by FEM simulation using coarse mesh shell element models. It was found that reduction of the reaction force due to crack propagation could be simulated by finding the elements adjacent to the crack and reducing the failure strain for those elements.

Experimental Study on the Strength of Collision Barriers in Nuclear Ships

The purpose of this study is to examine the ultimate strength of resisting type collision barriers which are installed in nuclear ships. Two kinds of ship side structures containing such barriers were designed by way of experiment as examples. The characteristic of one is that it consists of a grillage of horizontal and vertical webs, and the other's is that more deck plates are set than usual. Four series tests were carried out on these structures as follows, (1) one deck element model tests against a rigid bow model, (2) structural model tests against a rigid bow model, (3) double-hull element model tests against a rigid bow model, (4) structural model tests against two actual bow models.From the analysis of the test results, the collapse modes were classified into two patterns such as crushing collapse of only the loaded region and bending collapse of the whole structure. The strength in the former collapse could be attributed to the ultimate strength of the members which were carrying a load directly beneath it, where an effective sectional area, which was calculated by the effective width formula, was taken into account. The latter could be explained considering a limit load obtained by the plastic hinge method, where an effective full plastic moment, which was calculated with a sectional area excepting the ineffective parts due to buckling, was taken into account.Finally, a way to estimate ultimate strength was derived for the above-mentioned two kinds of ship side structures.