Grounding Accidents Research Articles

Verification of a simplified analytical method for predictions of ship groundings over large contact surfaces by numerical simulations

In this paper, a verification is presented of a simplified analytical method for the predictions from numerical simulations of structural performance during ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. This simplified analytical method was developed by Lin Hong and Jørgen Amdahl and calculates grounding characteristics, such as resistance and distortion energy, for double-bottomed ships in shoal grounding accidents. Two finite-element models are presented. One was built for a hold, and the other was built for a hold and a ship hull girder and also considers sectional properties, ship mass, added mass and the hydrodynamic restoring force. The verification was completed by comparing horizontal and vertical resistances and the distortion energy between seven numerical-simulation cases and a set of corresponding cases computed by a simplified analytical method. The results show that the resistances obtained by the simplified analytical method are close to the mean values of the resistance curves obtained by numerical simulations. The comparisons prove that the energy dissipation-prediction capability of the simplified analytical method is valuable. Thus, the simplified analytical method is feasible for assessing ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. Furthermore, studies of the influence of ship motion during groundings ascertained that ship motion affects structural performance characteristics. Resistances are lessened at the end of the grounding due to the reduction of indentations caused by heave and pitch motions of the ship hull girder. Finally, a new method for predicting the structural performance of the time-consuming complete-ship model by applying a combination of normal numerical simulations and ship-motion calculations is proposed and proven.

Probabilistic Approach to Predicting Residual Longitudinal Strength of Damaged Double HullVLCC

This paper estimates the residual longitudinal strength of a damaged double hull VLCC (Very Large Crude Carrier) under combined vertical and horizontal bending moments using Smith's method. The damage estimated in this study occurred due to collision or grounding accidents. The effects of the randomness of the yield stress, plate thickness, extent of damage, and the combination of these three parameters on the ultimate hull girder strength were investigated. Random variables were generated by a Monte Carlo simulation and applied to the double hull VLCC described by the ISSC (International Ship and Offshore Structures Congress) 2000 report.

A review of collision and grounding damage assessment methods

This review presents the latest methods to assess the structural damage during a collision or grounding accident. Therefore, recent research activities in the field of collision and grounding modelling and structural strength analysis are presented, thus contributing to the risk assessment related to these accidental events. As a result, a large-scale collision experiment is simulated and an actual tanker grounding accident to outline the applicability and to validated the selected methods. Additionally, the paper outlines research gaps and the need for unified and accepted assessment procedures for collision and grounding accidents.

A procedure to Assess the Damage of a Grounded Ship: A Full-Scale Validation Case Study

This paper concerns the analysis and simulation of a grounding accident from a structural point of view. A procedure is presented to assess the damage of a grounded ship. A non-linear finite-element method is used to simulate the bottom damage until a certain penetration or fracture limit is reached. An appropriate non-linear strain and stress measure describes the material behaviour including fracture. The procedure is validated against a case study of a grounded Suezmax tanker.

An oil outflow model for tanker collisions and groundings

In this paper we have developed an oil outflow model for collision and grounding accidents of tankers. The collision model explicitly links input variables such as tanker hull design (single or double), displacement and speed, striking vessel displacement and speed, and the interaction angle of both vessels to output variables: longitudinal and transversal damage extents of the tanker. Overlaying these damage extents on the tank vessel’s design yields an oil outflow volume totaling the capacity of the damaged tank compartments. A similar model is developed for grounding accidents. A total of 80,000 simulation accident scenarios described in the National Research Council SR259 report published in 2001 served as the joint data set of input and output variables used in this “linking” process. The oil outflow model herein was designed keeping computational efficiency in mind to allow for its integration with a maritime transportation system (MTS) simulation. We shall demonstrate the use of the oil outflow model as a final analysis layer to evaluate double-hull effectiveness in a geographic context of an MTS simulation model developed for the oil transportation routes traversing the environmentally sensitive San Juan Islands area in Washington State.

유조선의 선체손상 시 기름의 해상유출에 대한 실험적 연구

Crude oil carriers or product oil carriers are confronted with sea pollution due to hull damage from various accidents. To reduce the oil spillage of tankers, IMO(International Maritime Organization) and OPA 90(Oil Pollution Act 1990) adopted the hull structures of double skin type. In this study, oil spillage test of the double skin tanker with 1/100 scaled model was carried out under damaged condition due to collision and grounding accidents. A new structural type of oil tanker was also tested with pipe and valve system arranged in double side and single bottom hulls. Their results were compared with that of conventional type double hull on the view point of ship safety and oil spillage.

On the resistance to penetration of stiffened plates, Part I – Experiments

The paper deals with hull damage in ships which are subjected to grounding actions. A ship is assumed to settle vertically on a rock. It is further assumed that contact actions are local and restricted to one plate section. The scenario is analyzed by conducting a series of panel indentation experiments. Various configurations of stiffened panels are loaded laterally by a cone shaped indenter until fracture occurs. The specimen dimensions represent a 1:3 scale of the dimensions found in medium sized tankers. Naturally, because damaged hull and cargo tanks may have severe environmental consequences, e.g. as exemplified by high profiled grounding accidents such as the Exxon Valdez grounding which lead to the discharge of nearly 240,000 barrels of oil, focus is on the plastic deformation and fracture resistance of the panel. This is Part I of a two part companion paper. This paper reports observations from the experiments. Part II–Numerical Analysis deals with the numerical simulations of the same tests. Although, the attention is primarily focused on ship grounding, the experimental results are of considerable relevance for other types of abnormal actions, e.g. ship–ship collisions, dropped objects on deck structures, and stiffened panels subjected to explosions or ice actions.

Longitudinal strength reliability of a tanker hull accidentally grounded

This paper presents a reliability analysis of a damaged Suezmax double hull tanker, using a first order reliability method. The accidental grounding being analyzed is assumed to be centered on the keel, which is the worst possible scenario from a strength degradation point of view. The ultimate strength of the damaged tanker, to be used in the formulation, is calculated by means of a specific structural code, in which the damage is simulated by the removal of the damaged elements. Different sizes of the damage are analyzed and a relationship is established with the reliability index related to the ultimate strength. The wave induced loads are calculated from long-term distributions related to the “Global Wave Statistics” database. The still-water loads are defined from the ship loading manual. A parametric study about the impact of the ultimate bending moment of the damaged ship on the reliability index is then performed.

Effects of the Welding Residual Stress on the Grounding Damage Analysis of a Tanker

Vessels are rarely subjected to accidental loads such as the collision, grounding and stranding. But these accidental loads cause a lot of damages to hull structure including a large deformation, fracture, tearing and so on. In case of carrying dangerous goods such as crude oil, these accidents can induce a serious environmental pollution. All ocean-going vessels were made by welding. The welding residual stress is a significant shortcoming of welding remains at the hull structure, even though welding technology in shipbuilding field has provided a variety of advantages, e.g. remarkable shortening of the shipbuilding time. The aim of this paper is to investigate the effects of the residual stress in a grounding accident. When a ship runs aground against a sea-obstacle like a rock, this accident can be classified as a grounding. Among parameters of grounding accident scenarios such as the ship speed, the initial striking point, and loading conditions of the ship, only ship speed varies from 10 to 15 knots under ballast condition with/without consideration of residual stress(this sentence is not clear to the read). The initial striking point is at the bow of the center line of ship. A series of nonlinear numerical simulations with large deformation and fracture were carried out using LS-DYNA. As a result, two cases with residual stress have longer damage length. The difference seems to be relatively small, but not negligible.

Prevention of oil spill from shipping by modelling of dynamic risk

This paper presents a new dynamic environmental risk model, with intended use within a new, dynamical approach for risk based ship traffic prioritisation. The philosophy behind this newly developed approach is that shipping risk can be reduced by directing efforts towards ships and areas that have been identified as high priority (high risk), prior to a potential accident. The risk model proposed in this paper separates itself from previous models by drawing on available information on dynamic factors and by focusing on the ship’s surroundings. The model estimates the environmental risk of drift grounding accidents for oil tankers in real time and in forecast mode, combining the probability of grounding with oil spill impact on the coastline. Results show that the inherent dynamic risk introduced by an oil tanker sailing along the North Norwegian coast depends, not surprisingly, significantly upon wind and ocean currents, as well as tug position and cargo oil type. Results of this study indicate that the risk model is well suited for real time risk assessment, and effectively separates low risk and high risk situations. The model is well suited as a tool to prioritise oil tankers and coastal segments. This enables dynamic risk based positioning of tugs, using both real-time and projected risk, for effective support in case of a drifting ship situation.

Multi-stakeholder decision-making in the risk-based design of a RO-PAX double bottom for grounding

Grounding accidents can be fatal for ships. This paper discusses decision-making in risk-based design to avoid such outcomes for a 30 000 GT RO-PAX in a powered hard grounding. Five alternatives of a double-bottom structure are suggested to reduce the risks of loss of life, environmental damage, and material damage. Risk assessment concentrates on the consequences, applying numerical grounding simulations to model the energy absorption of the proposed alternatives. To determine the risks, 1295 Monte Carlo simulations are performed running a quasi-static model of ship motions. Accounting for these risks and the added production costs and operational loss, a new multi-stakeholder approach for selecting alternatives is proposed assuring simultaneous maximal satisfaction to both the shipyard and the ship owner. As an outcome, two alternatives are selected, the first increasing the bottom shell thickness by 50 per cent, and the second increasing the stiffness of longitudinal stiffeners by 90 per cent. If observing their performance, it is possible to recommend the latter as the most effective solution. Such an outcome is in accordance with the established practical opinions in increasing safety for grounding, proving sagacity of the presented approach.

風浪下における船体漂流に関する考察

A ship's drifting due to engine trouble was reported. In case that a ship's drifting due to engine trouble happens in shallow water and the ship drifts toward shore side, there is a possibility to cause a grounding accident. Especially the strong wind and high wave in rough sea produce the high drifting velocity. The high drifting velocity is pointed out in the report of the actual ship's drifting. The studies on ship's drifting before have been mainly conducted in deep water case with wind effect. For example since the accident of Nhodoka in the Japan Sea the studies on ship's drifting in deep sea under rough sea in the field of naval architects have been reported. On this study the author focused on the effect of wave drifting force against a ship's drifting in the shallow water besides wind effect.

Innovative Structural Designs of Tankers Against Ship Collisions and Grounding: A Recent State-of-the-Art Review

The double-hull design concept is one of the effective ways for oil pollution prevention during collision and grounding accidents of oil tankers. Arguably there might be better design alternatives which improve the structural performance of ships against collision and grounding when compared to the thus far well accepted double-hull concept, or even a double hull that is better in comparison to what is being routinely achieved by today's design methods. In this paper, a recent state-of-the-art review is undertaken on the literature related to more rational tanker structural design procedures and some innovative design concepts for tanker structures against ship collisions and grounding.

The safety of ferries: an accident injury perspective

This study investigates determinants of fatal and non-fatal injuries in ferry vessel accidents. Poisson regression estimates indicate that fatal and non-fatal injuries are 3.35 and 4.46% higher for fire/explosion than for material/equipment failure or grounding accidents, and 3.13 and 3.38% higher for multi-vessel than for single-vessel accidents. Non-fatal injuries are higher when the weather is foggy but less at night and the older the ferry. Estimated marginal effects indicate that every 100 fire/explosion accidents result in 6.1 fatal injuries, while each fire/explosion accident results in approximately one non-fatal injury.

GRACAT: software for grounding and collision risk analysis

From 1998 to 2000 an integrated software package for grounding and collision analysis was developed at the Technical University of Denmark within the project: Information technology for increased safety and efficiency in ship design and operation. The cost of the software development was 6 man-years. The software provides a toolbox for a multitude of analyses related to collision and grounding accidents. The software consists of three basic analysis modules and one risk mitigation module: (1) frequency, (2) damage, and (3) consequence. These modules can be used individually or in series and the analyses can be performed in deterministic or probabilistic mode. Finally, in the mitigation module risk profiles for the calculated consequences can be calculated and compared to alternative solutions by assignment of a cost function to the consequences. Thus, the possible analyses range from a deterministic crash analysis to a comparative risk analysis of two vessels operating on a specified route where the result is the probability density functions for the cost of oil outflow in a given area per year for the two vessels. In this paper, we describe the basic modelling principles and the capabilities of the software package. The software package can be downloaded for research purposes from www.ish.dtu.dk/GRACAT.

Analysis of hypothetical groundings in US waters

Because grounding accidents are rare events and data is sparse, their analysis requires a probabilistic approach. This paper illustrates an analysis of a large number of hypothetical, but realistic, grounding scenarios, and the application of an approach to study the effect of design modifications on the oil outflow performance. The scenarios are sampled from initial distributions of accident factors, which define grounding events. Structural damage and resulting oil outflow is then determined for double- and single-hull designs. The effect of the double-bottom height and structural modifications on the oil outflow is investigated.

Statistics and damage assessment of ship grounding

In this paper, general statistics of ship grounding incidents are considered and the damage extent distributions for Ro–Ro ships are presented from the results of a comprehensive damage data survey conducted using Lloyd's Register's damage database. Theoretical models and semi-empirical formulae based on parametric studies are used to study the damage extents of grounded ships. Two real life grounding accidents are assessed. One is a single hull VLCC grounded onto a single rock and the other is a cargo ship grounded onto multiple rocks. A simulation based on a simple multi-rock scenario has been conducted on a 304-m single hull tanker. Correlation is made between the present calculation method results, statistical results and IMO requirements. The paper concludes with the main findings from the study.

Cargo Ship Bunker Tanks: Designing to Mitigate Oil Spillage

Recent collision and grounding accidents have increased public and industry awareness of the risks of oil spills from bunker tanks. This paper summarizes historical spill data for freighters, and provides case histories for representative collision, allision, and grounding casualties. Arranging double-hull protection around the bunker tanks is one means for mitigating the risk of spillage. The location and size of the fuel oil tanks also influences the likelihood and expected volume of oil spills. The relative effectiveness of these alternatives are explored using probabilistic oil outflow analysis techniques collision of Alexia and Enit— Gult of Mexico, 1995

Absorbed Energy in Ship Collisions and Grounding—Revising Minorsky’s Empirical Method

Minorsky's well-known empirical formula, which relates the absorbed energy to the destroyed material volume, has been widely used in analyses of high-energy collision and grounding accidents for nearly 40 years. The advantage of the method is its apparent simplicity. Obviously, its drawback is that the absorbed energy does not depend on the arrangement of the structure, the material properties, and the damage mode. The purpose of the present paper is to establish a new simple relation between the absorbed energy and the destroyed material volume, which can be used as a design tool for analysis of ship collisions and grounding. The developed expressions reflect the structural arrangement, the material properties, and different damage patterns. The present method is validated against a large number of existing experimental results and detailed numerical simulation results. Applications to full-scale ship grounding accidents, the bottom raking damage to tankers and the bottom damage distribution for high-speed vessels are also presented. The proposed method may be considered as an improvement of the classical Minorsky method.

Effect of ship structure and size on grounding and collision damage distributions

It has been argued that a major shortcoming in the International Maritime Organization (IMO) Interim Guidelines for Approval of Alternative Methods of Design and Construction of Oil Tankers in Collision and Grounding is that grounding and collision damages normalized by the main dimensions of the ship have the same probability density distributions regardless of a particular structural design and ship size. The present paper explores analytical methods for assessing the overall effect of structural design on the damage distributions in accidental grounding and collisions. The results are expressed in simple expressions involving structural dimensions and the building material of the ships. The study shows that the density distribution for collision and grounding damages normalized by the main dimensions of the ship depends on the size of the ship. A larger ship has a higher probability of a larger relative damage length than that of a smaller ship in grounding damage. On the other hand, the damages to the side structure caused by ship collisions are found to be relatively smaller for large ships. The main conclusion is that the existing IMO damage distributions will severely underestimate the grounding damages to the bottom structure of larger vessels and to a lesser extent overestimate collision damages to the side structure of the hull.