Shengming Zhang

On Impact mechanics in ship collisions

Abstract The purpose of this paper is to present analytical, closed-form expressions for the energy released for crushing and the impact impulse during ship collisions. Ship–ship collisions, ship collisions with rigid walls and ship collisions with flexible offshore structures are considered. The derived mathematical models include friction at the contact point so that situation where the collision results in a sliding motion is included. Results obtained by application of the present procedure are compared with results obtained by time simulations and good agreement has been achieved. In addition, a number of illustrative examples are presented. The procedure presented in the paper is well suited for inclusion in a probabilistic calculation model for damage of ship structures due to collisions.

Plate tearing and bottom damage in ship grounding

A theoretical method for plate tearing by a rigid wedge is developed in this paper. The studied model is an idealization of ship-grounding and collision damage. The analysis model postulates that the plate curls up into two curved surfaces behind the wedge tip and that the plate material ahead of the wedge is tensioned and ruptured due to the direct pushing. Based on a parametric study, a semi-empirical formula is proposed for determining grounding force in the event of a ship running onto rocks in a high-energy grounding. The bottom strengths of single hull structures and double hull structures in ship-grounding incidents are compared. Finally, simple formulae for determining damage resistance and the extent of damage in ship grounding, expressed in terms of the ship principal particulars, are developed.

Statistics and damage assessment of ship grounding

Abstract 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 Lloyds Registers 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.

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

Abstract 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.

Effects of welding-induced residual stress on ultimate strength of plates and stiffened panels

During the welding of steel-plated structures, geometric distortions and residual stresses are developed. The influence of welding-induced geometric distortions and residual stresses on the compressive ultimate strength in longitudinal direction of plates and stiffened panels were investigated using nonlinear finite element analyses considering a range of plate thicknesses with various levels of residual stresses. The residual stresses in plates and stiffened panels have been modelled carefully and their effects on these structures due to welding-induced imperfections only are studied. The results and insights observed from the current study are presented.

Ultimate shear strength of plates and stiffened panels

Abstract This article presents work carried out on the ultimate shear strength of plates and stiffened panels. A simple formula for assessment of the ultimate shear strength of plates and stiffened panels was developed and is described. The proposed formula was verified against results from ABAQUS non-linear finite element software and a large number of published results. Good correlation was achieved. The method was also compared with published formulae and design codes. Application of the proposed method to the side shell structure of a double hull oil tanker of uniform thickness and non-uniform thickness was carried out and the results were found to compare favourably with results from ABAQUS. The method was also applied to collision damaged side shell structures.

A review and study on ultimate strength of steel plates and stiffened panels in axial compression

This paper presents a review and study on ultimate strength analysis methods for steel plates and stiffened panels in axial compression. Buckling and collapsing mechanisms of steel plates and stiffened panels are described. Analysis approaches for ultimate strength and their employments in ship designs are reviewed and discussed. A study and further validation on the authors developed formula for ultimate strength of stiffened panels using a comprehensive non-linear finite element analysis, 110 models in total, and a wide range of model test results, 70 models in total, are carried out. Finally, applications of the developed formula to existing oil tankers and bulk carriers are presented.

Collisions damage assessment of ships and jack-up rigs

Ship collision with offshore installations is one of the key concerns in design and assess of platforms performance and safety. This paper presents an analysis on collision energy and structural damage in ship and offshore platform collisions for various collision scenarios. The platform or rig is treated as either rigid or flexible and its sensitivity on collision energy and structural damage is studied. An application example where an ice-strengthened supply vessel collides against a jack-up rig is analysed and the crushing resistance of the involved thin-walled structures is evaluated.

A method for ship collision damage and energy absorption analysis and its validation

ABSTRACT For design evaluation, there is a need for a method which is fast, practical and yet accurate enough to determine the absorbed energy and collision damage extent in ship collision analysis. The most well-known simplified empirical approach to collision analysis was made probably by Minorsky, and its limitation is also well-recognised. The authors have previously developed simple expressions for the relation between the absorbed energy and the damaged material volume which take into account the structural arrangements, the material properties and the damage modes. The purpose of the present paper is to re-examine this methods validity and accuracy for ship collision damage analysis in ship design assessments by comprehensive validations with experimental results from the public domain. In total, 20 experimental tests have been selected, analysed and compared with the results calculated using the proposed method. It can be concluded that the proposed method has a good accuracy with the mean value of 0.988 and standard deviation of 0.042.

Experimental investigation on the effect of low temperatures on the fatigue strength of welded steel joints

There are an increasing number of liquefied natural gas ships and oil tankers that are intended for navigation in ice and cold climates, and as such, there is a necessity to assess the risk of fatigue damage to these ships. A significant aspect of the fatigue assessment is the performance of steels when subject to low temperatures. This paper presents the results of an investigation on the fatigue strength of welded steel joints at low temperatures and discusses some of the associated issues. The paper presents the results of cyclic tension fatigue testing of welded specimens made from AH36 and DH32 steel grades under room and cold temperature conditions. Nominal fatigue curves for these specimens and crack lengths as a function of loading cycle number are also provided. The fatigue strength of welded specimens of DH32 and AH36 steel grades has been obtained. The data can be used for the evaluation of the fatigue life of ship structures manufactured from the specified steel grades and can be used for establishing whether measures need to be taken to reduce the risk of fatigue damage in the structural elements of ships trading in cold climates.