Safety guidelines of ultimate hull girder strength for grounded container ships
Introduction
Accidents involving ships and offshore structures such as grounding, collision, fire and explosion occur even when many preventive actions have been taken. Due to increasing environmental and safety concerns, it has become necessary to reduce the probability of accidents and minimize the damage once an accident has taken place (IMO, 2003, Paik et al., 2003, Pedersen, 2010). A large number of studies on grounding accidents have been carried out in terms of damage predictions (Simonsen and Hansen, 2000), structural consequences (Paik, 2007a, Paik, 2007b), hull girder collapse (Pedersen, 1994, Paik et al., 1998, Wang et al., 2000, Luis et al., 2009), risk assessment (Soares and Teixeira, 2001) and structural analysis method (Ohtsubo et al., 1994, Kim et al., 2013). Some of the recent studies on grounding accidents are reported in (Samuelides et al., 2009, Pedersen, 2010, Nguyen et al., 2011, Hong and Amdahl, 2012).
This study focuses on hull girder collapse in container ships that have sustained grounding damages by analyzing ships in the following sizes: 3500TEU, 5000TEU, 7500TEU and 13,000TEU. The purpose is to develop a procedure for defining an acceptance damage criterion and making rapid salvage plans or rescue schemes for container ships after a grounding accident.
Paik et al. (2012) proposed an innovative method for assessing the safety of a ship which has suffered accidental or in-services damages. Only a small number of probable scenarios for accidental or in-service damage representing all possible scenarios are selected using a sampling technique in which the random variables affecting the damage are probabilistically characterized. A damage index for the corresponding damage scenario is identified as a function of damage characteristics such as location and extent of the damage. The residual strength performance of a ship with the corresponding damage scenario can then be calculated by analytical or numerical methods. Once this process has been carried out for each of the damage scenarios selected, a diagram relating the residual strength performance to the damage index (abbreviated as the R–D diagram) can be established. This diagram will be very useful for a first-cut assessment of a ship’s safety immediately after it has suffered structural damage. The diagram can also be used to determine acceptance criteria for a ship’s safety against accidental or in-service damage. The R–D diagram method (Paik et al., 2012) was proven to be useful through an applied example on a diagram between the ultimate longitudinal strength versus grounding damage index for four types of double hull oil tankers – VLCC, Suezmax, Aframax and Panamax.
The present paper deals with another application of the Paik’s method to the safety of container ships which have suffered structural damage by grounding. Four sizes of real container ships are considered: 3500TEU, 5000TEU, 7500TEU and 13,000TEU.
Section snippets
Target container ship hull structures
Four types of container ships (3500TEU, 5000TEU, 7500TEU and 13,000TEU) are considered in this study to develop the R–D diagram for grounding damage. Fig. 1 shows the mid-ship section designs of the four ships in which L is ship’s length between perpendiculars, B is ship’s breadth, D is ship’s depth, b is double-side width, and h is double bottom height. Note that the B/D ratio increases in all but the 13,000TEU class container ship.
Procedure for the development of residual strength – damage index diagram
The general procedure for the development of an R–D diagram is shown in Fig. 2 (Paik et al., 2012). Once a ship’s structural characteristics have been defined, including its geometry, dimensions, and material properties, a limited number of probable damage scenarios representing all possible scenarios can be selected by a probabilistic approach.
Each parameter affecting the structural damage is dealt with as a random variable and it shall be characterized probabilistically. In the present paper,
Results for FOUR container ship types under grounding accident conditions
The R–D diagrams in this study are established based on the residual ultimate strength of the ship’s mid-section. An analysis of the four container ship sizes is undertaken using their gross scantlings, which means that the corrosion effect is not considered.
Use of the developed R–D diagrams
The R–D diagrams and corresponding R–D formulations developed here can be used as a first estimate of the residual ultimate longitudinal strength performance of container ships immediately after a grounding accident has occurred when the location and amount of grounding damage is approximately known. The R–D diagrams can also be used to determine the acceptance criteria for grounding strength performance. For example, IMO (2000) specifies requirements that the ultimate longitudinal strength of
Conclusions
The aim of the present paper has been to develop residual ultimate longitudinal strength – grounding damage index (R–D) diagrams for container ships in association with the innovative method (Paik et al., 2012) which was proven to be useful through an applied example on the grounding strength performance for four types of oil tankers: VLCC, Suezmax, Aframax and Panamax.
In the present paper, the grounding strength performance for four types of container ships, i.e. 3500TEU, 5000TEU, 7500TEU and
Acknowledgments
This study was undertaken by the Lloyd’s Register Foundation Research Centre of Excellence (The Ship and Offshore Research Institute) at Pusan National University, Korea. The LRET is an independent charity working to achieve advances in transportation, science, engineering and technology education, training and research worldwide for the benefit of all. The research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) and funded by the
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