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A simple method for the rapid assessment of ship bottom structures subjected to grounding over seabed obstructions with large contact surfaces is proposed in this paper. It has been recognised that the shape and size of the seabed obstruction is of crucial importance in relation to the characteristics of bottom damage. Most studies on ship grounding are concerned with ‘rock-type’ sharp obstructions, where plate tearing is the dominating failure mode. However, very few studies are found related to grounding over blunt obstructions with large contact surfaces such as ‘shoals’. Denting rather than tearing is more likely for the bottom plating as observed from actual grounding incidents. The sharp obstruction may cause earlier penetration and result in very unfavourable consequences such as compartment flooding. In contrast, the bottom plating may not fracture when moving over a blunt-type sea floor. But it may threaten the global hull girder resistance and give rise to even worse consequences such as hull collapse. The proposed simple method is established on the basis of a series of closed-form solutions for individual structural members developed from the plastic mechanism analysis. The primary deformation modes for the major bottom structural members are sliding deformation of longitudinal girders, denting and crushing of transverse members and indentation of bottom plating. The effect of friction is considered and estimated in a simple manner. The vertical resistance that governs the vertical ship motion is derived. It is found that the vertical resistance is free of friction. The proposed simple method for bottom strength is verified against large-scale non-linear finite element analyses, where a good correlation is obtained. [ABSTRACT FROM PUBLISHER]

Abstract: The objective of the present paper is to study the oil flows from damaged ships with different tank designs during collision and grounding incidents. For this purpose, analytic models of instantaneous oil spills are proposed, and CFD simulations with FLUENT software were carried out. Experimental tests were also designed and performed. These experimental tests are intended to verify the performance of the proposed model and CFD simulations and to investigate the fluid dynamics of accidental oil spills caused by grounding and collision. The results from the tests provide some quantitative information on the behavior of oil spills from damaged tanks with different tank designs that are either below or above the waterline. The model tests also show how the space between the inner and outer hull will capture the oil that is spilled from the main cargo tank. The effectiveness of these spaces in terms of retaining the oil is influenced by the tank designs and opening conditions. In general, the double-hull design has the best performance, while the double-side and the double-bottom design help to reduce the oil spill and increase the oil spill time. [Copyright &y& Elsevier]

Abstract: The paper presents a simple procedure to estimate the damage to a ship bottom and the associated seabed topology that results from a dynamic grounding event. The seabed is modeled as a rigid body and parameterized by a quadratic surface, i.e., a paraboloid, which can in principle model a wide range of seabed topologies. A nonlinear finite element program (LS-DYNA) is used to simulate the contact force versus the lateral penetration, from which the horizontal force component of powered grounding is estimated. The simplified procedure for analyzing dynamic and static grounding events is outlined. Simulations are performed for different ship speeds and for different initial levels of obstruction over the keel. It is shown that a static approach may replace the dynamic grounding simulation, thereby considerably reducing the computational work. The static approach allows for the quick estimation of the energy absorption during powered grounding, which is imperative for decision making during critical situations. The ultimate goal of the study is to provide a near real-time prediction of the risk of rupture of the cargo tanks and hull girder failure. Moreover, the residual strength of damaged ships is an important issue that is related to operations involved in the salvage of wrecked vessels, such as re-floatation and towing. [Copyright &y& Elsevier]

Abstract: A new theoretical model for the crushing of web girders under localized in-plane loads is proposed on the basis of a comparative study of existing simplified methods and analyses of the progressive deformation process of web girders. The model captures several features of the local crushing process of the girder which have not been accounted for by any of the existing models. The behavior of web girders under in-plane loads is a relevant subject in both ship collision and grounding process as well as in the area of civil engineering. A variety of simplified methods have been proposed and developed by various authors around the latest decade. The different formulations in terms of instantaneous and mean crushing force are investigated and reproduced under some common rules for a comparative study. The predictions are compared to three series of experimental results found in literature. The applicability and correlations of these simplified methods are discussed in some detail. It is observed from the analysis of the deformation process that the existing theories cannot capture the main characteristics of the progressive crushing process. Therefore, a new simplified deformation model is proposed comprising two folding elements with the second folding element compressed partly, and a new set of simplified analytical method is developed by using plastic methods of analysis. The proposed method is verified by the three experiments, which have been used for the comparative study, and it agrees satisfactorily with the experimental results. For the purpose of practical application of the present simplified formulae, the effect of web stiffeners on the crushing resistance is studied as well as the influence of dynamic loading and the effective crushing distance. [Copyright &y& Elsevier]

Abstract: This study proposes a new procedure for the estimation of stranding forces and their contact positions. The method is based on the measurement of a few characteristic on-site parameters, i.e., the draughts and bending moments acting on a stranded ship. A procedure that estimates penetration into the ship bottom based on knowledge of the resistance versus penetration relationship is also presented. The seabed topology is parameterized by a paraboloid. This geometry can, in principle, characterize a wide range of obstructions, from sharp rocks to large shoals. Nonlinear finite element analysis is used to simulate various stranding situations and to generate the corresponding resistance versus penetration curves. The present method provides insight into the identification of real stranding scenarios in terms of the location of obstructions, their possible shapes and the corresponding resistance-penetration curves. The proposed methodology represents a first step towards a tool for quick decision making during salvage operations. The ultimate goal is to allow near real-time prediction of the risk of penetration into cargo tanks and hull girder failure. To demonstrate the effectiveness of the proposed method, it is applied to a simulated trial stranding scenario. [Copyright &y& Elsevier]