Striking Ship Research Articles

Extension of the super-elements method to the analysis of a jacket impacted by a ship

The aim of this paper is to present a simplified analytical method for estimating the crushing resistance of an oblique cylinder impacted by the stem of a striking ship. The collision angle of the vessel is arbitrary, i.e. oblique collisions are also considered in this article. The two extremities of the tube are assumed to be clamped. These developments are intended to be used for evaluating the crashworthiness of an offshore wind turbines jacket. To achieve this goal, closed-form expressions are first derived for the particular situations of a horizontal and a vertical cylinder by applying the upper-bound method. An interpolation formula is then proposed to get the resistance opposed by the tube for any inclination angle. In order to validate these theoretical developments, some comparisons are made with the results of numerical simulations. These latter are performed using the finite elements software LS-DYNA. In almost all cases, the analytical prediction of the resistance is found to be in quite good agreement with the numerical ones. Finally, another comparison is made by simulating an OSV collision with a full jacket. In this case, the theoretical model is found to be insufficient for large impact energies and points out the need of further research.

A framework for risk assessment for maritime transportation systems—A case study for open sea collisions involving RoPax vessels

Maritime accidents involving ships carrying passengers may pose a high risk with respect to human casualties. For effective risk mitigation, an insight into the process of risk escalation is needed. This requires a proactive approach when it comes to risk modelling for maritime transportation systems. Most of the existing models are based on historical data on maritime accidents, and thus they can be considered reactive instead of proactive.This paper introduces a systematic, transferable and proactive framework estimating the risk for maritime transportation systems, meeting the requirements stemming from the adopted formal definition of risk. The framework focuses on ship–ship collisions in the open sea, with a RoRo/Passenger ship (RoPax) being considered as the struck ship. First, it covers an identification of the events that follow a collision between two ships in the open sea, and, second, it evaluates the probabilities of these events, concluding by determining the severity of a collision. The risk framework is developed with the use of Bayesian Belief Networks and utilizes a set of analytical methods for the estimation of the risk model parameters.Finally, a case study is presented, in which the risk framework developed here is applied to a maritime transportation system operating in the Gulf of Finland (GoF). The results obtained are compared to the historical data and available models, in which a RoPax was involved in a collision, and good agreement with the available records is found.

A simplified analytical method for estimating the crushing resistance of an inclined ship side

This paper provides a new contribution to the simplified analytical treatment of collisions between two ships. It is directly connected to the well-known super-elements method, which is a simplified procedure allowing for a quick estimation of the damages caused to both the striking and struck vessels during such events. In this article, a new analytical formulation is presented for estimating the impact resistance provided by inclined ship side panels. Two different scenarios are treated. We first deal with the case of an impact between the oblique plate and the stem of the striking ship, and then we consider the situation where the inclined panel is impacted by the bulb. For these two scenarios, an analytical formulation relating the force and the penetration is provided and these developments are validated by comparing them to the results of finite elements simulations. Finally, the new inclined plate super-element is integrated in a simplified model of a frigate collided by another ship, and the resistance given by the super-elements method is then compared to the one obtained by a numerical simulation of this collision.

Analysis of ship–ship collision damage accounting for bow and side deformation interaction

This paper presents a procedure to analyse ship collisions using a simplified analytical method by taking into account the interaction between the deformation on the striking and the struck ships. Numerical simulations using the finite element software LS-DYNA are conducted to produce virtual experimental data for several ship collision scenarios. The numerical results are used to validate the method. The contributions to the total resistance from all structural components of the collided ships are analysed in the numerical simulation and the simplified method. Three types of collisions were identified based on the relative resistance of one ship to the other. They are denoted Collision Types 1 and 2, in which a relatively rigid ship collides with a deformable ship, and Collision Type 3, in which two deformable ships are involved. For Collision Types 1 and 2, estimates of the energy absorbed by the damaged ships differ by less than 8% compared to the numerical results. For Collision Type 3, the results differ by approximately 13%. The simplified method is applicable for right angle ship collision scenario, and it can be used as an alternative tool because it quickly generates acceptable results.

Study on Collision Damage Behavior of Ship

Ship collision is a kind of dangerous accident which may result in serious damage of struck hull structure during shipping process. The damage of ship depends on the relative rigidity of striking ship and the capabilities of crash resistance of ship structures. The rigidity of bow is always considered as higher than that of side, so the structure of bow is regarded as rigid body. But this method is so conservative that the result of numerical simulation may be wrong when the rigidity of side of one ship is higher than that of bow of another ship. The process of collision of two ships is simulated, in which the structures of two ships are all defined as elastic body. The behavior of side is studied and some useful results are found.

An extensive study of a ship's survivability after collision – A parameter study of material characteristics, non-linear FEA and damage stability analyses

Throughout the world, ships are continuously being declared as total losses and a significant part of these accidents are collisions between ships. The International Maritime Organization strives towards a more risk-based view on addressing the damage stability of ships. The current study addresses the survivability following a ship collision by the use of a sequential (de-coupled) computational methodology. The methodology is comprised of structural analysis of a collision scenario followed by dynamic damage stability simulations of the struck ship in order to establish the time to capsize of the struck ship. The emphasis of the current investigation is on the structural computations of the collision event; explicit finite element analyses are presented for a case study of a collision scenario. In particular, uncertainties of input parameters in the finite element simulations and their impact on the shape and size of the damage opening area, and time to capsize of the struck ship, are addressed. Material modelling aspects are studied; scatter in material properties within a material class as well as damage modelling. In addition, the effects of using a deformable or rigid striking bow section, the friction coefficient, the collision angle and the speed of the striking ship are studied. On the basis of the results presented, assumptions commonly used in these kinds of analysis are discussed. Recommendations for a sufficient level of simplifications for arriving at reliable results in numerical simulation of ship collisions are made.

Simplified Analytical Method for Estimating the Resistance of Lock Gates to Ship Impacts

The present paper is concerned with the design of lock gates submitted to ship impacts. In this paper, a simplified analytical method is presented to evaluate the resistance of such structures under collision. The basic idea is to assume that the resistance is first provided through a local deforming mode, corresponding to a localized crushing of some impacted structural elements. For consecutive larger deformations, the resistance is then mostly provided through a global deforming mode, corresponding to an overall movement of the entire gate. For assessing the resistance in the case of the local deforming mode, the structure is divided into a given number of large structural entities called “superelements.” For each of them, a relation between the resistance of the gate and the penetration of the striking ship is established. However, as some results are already available in the literature, this subject is not treated extensively in this paper. On the contrary, the calculation of the resistance of the gate provided through the global mode is detailed and the strategy to switch from local to global deformation is highlighted. Finally, we propose to validate our developments by making a comparison between results obtained numerically and those predicted by the present analytical approach.

Survivability analysis of a struck ship with damage opening – influence from model and material properties uncertainties

The conditions for damage stability and survivability of a ship struck in a collision in arbitrary sea-state are, from a structural point of view, determined by the size and shape of the damage opening in its side-shell. In the current investigation, explicit finite element analyses (FEA) are presented of a ship-to-ship collision scenario in which the damage opening of a struck ship is calculated for a selection of damage degradation models and realistic material properties, here referred to as model and material properties uncertainties. The model uncertainty is considered as a possible (user-related) insecurity in the selection of the most appropriate damage criterion for the analysis; the shear failure and the forming limit diagram (FLD) criteria were compared in the current investigation. The uncertainty in material properties is accounted for in the constitutive material model description and the material parameters used in the two damage criteria. The size and shape of the damage openings predicted by the FEA are used in damage stability analyses in which the struck ship is subjected to wave motions in an arbitrary sea-state and flooding into the damage opening. The survivability of the struck ship is estimated for all of the damage opening cases. One of the main conclusions is that the high degree of accuracy that a researcher on structure analysis strives for has to be considered together with the natural variation of the sea-state that defines the characteristics in the following damage stability analysis. Consequently, by adoption of a holistic approach in which structural integrity and damage stability research are combined using a systematic parameter (sensitivity) and collision-scenario-based analysis, simplified models and criteria can be developed more efficiently and with higher precision. It will also be clearer which variables are the most important to focus on when analysing the survivability or risk for capsizing.

Finite element simulations of ship collisions: a coupled approach to external dynamics and inner mechanics

The paper presents a method for dynamic numerical simulations of ship collision with LS-DYNA. The method can be employed to simulate the ship motions and the structural deformations during the collision. The proposed model treats the external dynamics and the internal mechanics simultaneously and thus includes the possible interaction. The ship motions are limited to the horizontal plane of water. The simulation method considers precisely the most important force components – inertia force and the contact force – while neglecting buoyancy, gravity and restoring forces. The striking ship is modelled as a rigid bulb with a number of discrete mass points attached to it. The side structure of the struck ship is modelled in detail in the collision area; the rest of the struck vessel is also modelled with discrete mass elements. The paper describes a numerical simulation of an eccentric collision at an inclined angle and compares the outcomes to the experimental measurements. The numerical simulation results agree well with the experiments, implying the validity of the method.

2010 Best Paper Award

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.

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.

Numerical and experimental motion simulations of nonsymmetric ship collisions

A calculation model to simulate nonsymmetric ship collisions, implying an arbitrary impact location and collision angle, is described in the paper. The model that is introduced is based on the time integration of twelve equations of motion, six for each ship. The motions of the ships are linked together by a mutual contact force. The contact force is evaluated as an integral over the surface tractions at the contact interface. The calculation model provides full time histories of the ship motions and the acting forces. Physical understanding of the underlying phenomena was obtained by a series of model-scale experiments in which a striking ship collided with an initially motionless struck ship. In this paper, numerical simulations of four nonsymmetric collisions are presented and the calculations are validated with the results of the experiments.

Sloshing interaction in ship collisions—An experimental and numerical study

Sloshing interaction in ship collisions is studied both experimentally and numerically. The rapid change in ship motions resulting from contact loading in collisions initiates violent sloshing inside partially filled liquid tanks on board. Sloshing affects the collision dynamics and reduces the amount of energy available for structural deformations. An understanding of this interaction phenomenon was obtained by a series of model-scale experiments, in which a striking ship, with two partially filled tanks, collided with an initially motionless struck ship without any liquid on board. The influence on the structural deformation of the fluid mass in the tanks and the velocity of the collision was studied. Numerical simulations of the cases were performed, combining a linear sloshing model with a theoretical collision model. The simulation model was validated with experimental results and good agreement was achieved in the case of medium filling levels in the tanks, while correspondingly the deformation energy was overestimated by up to 10% for shallow filling levels.

A study on collision buffer characteristic of sharp entrance angle bow structure

SEA-Arrow (sharp entrance angle bow like an arrow) has no protrusion of the bulbous bow to reduce bow waves and has a transverse stiffening system in the narrow bow space to apply the buffer bow concept. This system has lower longitudinal stiffness than a conventional longitudinal stiffening system and therefore has buffer characteristic in ship-to-ship collision. A comparative collision study of SEA-Arrow and the conventional bulbous bow was conducted using elasto-plastic finite element analysis. A collision scenario where the striking ship hits the side shell of tanker midship perpendicularly was selected. The results showed that the buffer bow characteristic of SEA-Arrow is superior to that of the conventional bulbous bow, since much more energy is dissipated by the plastic deformation of striking and struck ships until the inner shell of struck ship ruptures.

On the global ship hull bending energy in ship collisions

During ship collisions part of the kinetic energy of the involved vessels immediately prior to contact is absorbed as energy dissipated by crushing of the hull structures, by friction and by elastic energy. The purpose of this report is to present an estimate of the elastic energy that can be stored in elastic hull vibrations during a ship collision. When a ship side is strengthened in order to improve the crashworthiness it has been argued in the scientific literature that a non-trivial part of the energy released for structural deformation during the collision can be absorbed as elastic energy in global ship hull vibrations, such that with strong ship sides less energy has to be spent in crushing of the striking ship bow and/or the struck ship side. In normal ship–ship collision analyses both the striking and struck ship are usually considered as rigid bodies where structural crushing is confined to the impact location and where local and global bending vibration modes are neglected. That is, the structural deformation problem is considered quasi-static. In this paper a simple uniform free–free beam model is presented for estimating the energy transported into the global bending vibrations of the struck ship hull during ship–ship collisions. The striking ship is still considered as a rigid body. The local interaction between the two ships is modeled by a linear load–deflection relation. The analysis results for a simplified model of a struck coaster and of a large tanker show that the elastic energy absorbed by the struck ship normally is small and varies from 1 to 6% of the energy released for crushing. The energy stored as elastic global hull girder vibrations depends on the ship mass, the local stiffness of the side structure, and of the position of contact. The results also show that in case of highly strengthened ship sides the maximum global bending strains during collisions can lead to hull failure.

Scenarios for the assessment of the collision behavior of ships

Since the late fifties, when the first nuclear powered merchant ships were designed, collision research has been focused on the establishment of models for the prediction of the damage of the side of a ship involved in a ship-ship collision. Such models have been used to assess the performance of the struck ship in case she is involved in a collision. Further it was and it is still highly desirable to develop design tools which could provide guidance for the construction of ship hulls which will minimize as far as possible the risk in case of a collision. In order to assess the collision behaviour of a ship, there is a need to test her under specific collision incidents, which are described by a number of parameters, such as the particulars of the striking ship including the stiffness of her bow, the speeds and relative orientation of the two vessels, sea conditions, etc. The assessment methodologies are deterministic, i.e. they are based on one or a few severe collision scenarios, or probabilistic, i.e. they consider distribution functions of one or more collision parameters. The paper presents and discusses existing codes concerning collision scenarios for floating and fixed marine structures, presents data that can be used for the determination of the level of the loading that a ship may experience if she is involved in a collision and gives examples of relevant calculations.

주변 유체를 고려한 선박 충돌해석 기법 연구

Collision analysis problems between ship to ship can be generally classified into the external mechanics(outer dynamics) and internal mechanics(inner dynamics). The former can be also dealt with the concept of fluid-structure interaction and the use of rigid body dynamic program, depending on the ways handling the hydrodynamic pressure due to surrounding water. In this study, full scale ship collision simulation was carried out, such as a DWT 75,000 ton striking ship collided at right angle to the middle of a DWT 150,000 struck ship with 10 knots velocity, coupling MCOL, a rigid body mechanics program for modeling the dynamics of ships, to hydrocode LS-DYNA. It could be confirmed that more suitable damage estimation would be performed in the case of the collision simulations with consideration of surrounding water through the comparison with the collision simulation results of fixed struck ships without it. Through this study, the opportunity could be obtained to establish a more effective ship collision simulation technique between ship to ship.

緩衝型船首構造の耐衝突性能

We still have experienced cargo oil spill from a struck D/H(double hull) tanker like the accident case of “Baltic Carrier (at Denmark in 2001)”. “Buffer Bow” has come to be considered as an innovative strategy following after D/H system to prevent marine environmental pollution. The mission expected to buffer bow is “minimizing the damage on the struck ship” and thus “decreasing the risk of oil outflow from struck D/H tankers” when it encounters collision accidents. This performance is supposed to be realized by such structural characteristics as “to be crushable” and “to have high energy capacity in the internal mechanics”. As the measures to represent the performance level of buffer bow the critical striking velocity (VB,cr) and the critical collision angle (θcr) are proposed. Those critical events are defined as the threshold where the inner hull of struck tanker is ruptured or not.As it has been confirmed in the preliminary investigation that the bulb structure is most threatening to struck ships, buffer bow design considered is focused on bulb structure. The buffer bow design items which are supposed to be effective are (1) blunt shaped configuration, (2) transverse stiffening system and (3) adopting minimum shell thickness. The advantage expected to those design items are the fact that no special equipments nor special materials are needed. Their contributions have been evaluated through a series of FEM simulation analyses adopting a VLCC as the model struck ship, and VLCC's and container ships as the threatening striking ships. The effectiveness of buffer bow is confirmed by comparing the performance of the critical striking velocity and the critical collision angle between buffer bows and standard bows.At the final stage the effect of buffer bow is evaluated by focusing on the performance that how much the risk of oil outflow is decreased. “The mean oil outflow” is derived based on probabilistic procedure considering dangerous collision scenarios. The case study has shown that the probabilistic oil outflow is decreased by about 80% if buffer bow design is adopted to VLCC.

The effect of selected parameters on ship collision results by dynamic FE simulations

The purpose of the paper is to study the effect of selected design parameters on crashworthiness of the struck ship. The dynamic collision process is simulated by the ABAQUS/Explicit code, and two problems are analysed: (1) a plate struck by a cone, and (2) a collision of two ships. The first problem, of a plate struck by a rigid cone, has a preliminary character and validates our FE modelling; a similar crushing force is obtained as in Amdahl and Kavlie (DNV-MIT Workshop on Mechanics of Ship Collision and Grounding, DNV H øvik, Oslo, September) and Simonsen (ISESO Report No. I108.02.02.052.004, Department of Naval Architecture and Offshore Engineering, Technical University of Denmark, April), despite the differences in methods of analysis applied. The current computations go further than the cited papers, and assess the dependence of results on the material model of the plate (including failure), the contact within the plate interior, and the mass of the striking cone. The second problem is of practical interest, as it concerns a collision of a double hull crude oil carrier ship and a container vessel with a bulbous bow. The progress of deformation in time is monitored including large plastic strains as well as contact between the ships, which allows to model crushing and tearing. The effect of the following parameters is assessed: the material model of the struck ship, the friction coefficient for the contact between the vessels, the initial velocity of the striking ship, the motion of the struck ship, and the mass scaling option used to accelerate computations. The included results present the deformed struck objects, and also the crushing force and various types of energy vs. penetration of the striking body. Conclusions are formulated regarding the numerical method used, the striking ship velocity data and the material model for the struck ship.

Predicting Resistance of Spherical-Type LNG Carrier Structures to Ship Collisions

The modern design of steel structures uses limit states classified into four types, namely, serviceability limit state, ultimate limit state, fatigue limit state and accidental limit state. The aim of this paper is to propose and illustrate a procedure to assess the capability of a spherical-type LNG carrier of 135 000 m3 to resist ship collisions. An assessment procedure based on the energy dissipation capability relating to structural crashworthiness can, in this case, be applied to protect spherical LNG cargo tanks from fracture in minor or moderate collision accidents as shown in the paper. In the procedures developed, while the loss of kinetic energy during the collision accident is approximately estimated by applying the momentum equilibrium of the two implicated ships, a series of relatively sophisticated numerical computations is under- taken to simulate the structural crashworthiness of the object ship in the full load condition at standstill, varying the loading conditions and types of the striking ship, when the LNG carrier side structure is considered to be struck by the bow of either a VLCC or another LNG carrier. Based on the computed results, the collision resistance indices (CRI), which in the present study are defined as a function of the ratio of the structural energy dissipation capability to the initial kinetic energy loss, are calculated for the object ship for various collision scenarios. Some important insights useful for preventing collision damage of the spherical LNG cargo tanks of the ship are also discussed.