Rapid assessment of ship grounding over large contact surfaces

Abstract

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.

Analytical Models for the Response of the Double-Bottom Structure to Underwater Explosion Based on the Wave Motion Theory

“…In this figure, the FE prediction is a constant. To get the same value as the FE prediction, we have to change the value of ( ) in (27). By comparing the curves in Figure 24(a), we can easily solve (27) by setting ( ) = 15.…”

“…Figure 24(a) shows the comparison between the FE prediction (obtained from (28)) and the analytical solution (obtained from (27)) for the nondimensional impulse maximum ,max . In this figure, the FE prediction is a constant.…”

“…To obtain the solution of (27), an analytical solution and FE simulation are carried out. The FE modeling process is the same as in Section 3.1.…”

“…Analytical models for study of the double-bottom structures response are rare. When analyzing a tanker grounding accident, the total response of the assembly is obtained through the summation of the responses of all structural members [26,27]: plates, cruciform, and stiffeners. Based on similar models, a potential alternative simplified calculation model for the total response of the double-bottom can be obtained in two steps.…”

Comparison of residual strength-grounding damage index diagrams for tankers produced by the ALPS/HULL ISFEM and design formula method

“…Research on grounding accidents conducted by Pedersen (2010), Nguyen et al (2011) and Hong and Amdahl (2012) may also be referred.…”