Approach to Simulate Dynamic Elasto-Plastic Whipping Response of Global Hull Girder of a Large Container Ship Due to Slamming Load
- Yasuhira Yamada (National Institute of Maritime / Port and Aviation Technology)
- Document ID
- International Society of Offshore and Polar Engineers
- The 29th International Ocean and Polar Engineering Conference, 16-21 June, Honolulu, Hawaii, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. International Society of Offshore and Polar Engineers
- container ship, whipping, dynamic ultimate strength, non-linear finite element analysis, slamming
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- 24 since 2007
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The purpose of the present study is to try to develop a methodology to simply simulate dynamic elasto-plastic structural response of global hull girder of ships subjected to slamming load using a large scale nonlinear finite element model. The main focus is laid on relation between slamming induced whipping and dynamic collapse behavior of hull girder, which is very important to prevent breaking of ships.
A series of time domain FE-simulation is carried out using a large-scale FE model of a 8000 TEU container ship where slamming load is applied to the bow bottom. The ship is modeled by elaso-plastic elements at midship region and other regions are modeled by rigid elements, consequently “two-node vibration mode” can be simulated. Hull-girder vertical bending moment as well as occurrence of breaking of ship are investigated by varying the load time duration of the slamming load which is modeled by sinusoidal impulse. In order to carry out time domain simulation explicit analysis is adopted instead of implicit analysis. It is found from the present study that structural response and dynamic ultimate strength are largely dependent on load time duration of hogging moment. Collapse mechanism of global hull girder depending on time duration of load are discussed in detail.
As ship length increases and hull structure becomes more flexible, the hull girder vibration due to springing and whipping plays a key role in the strength of ocean-going vessels, especially for large/ultra-large container carriers.
Hull breaking accidents
In 2013 8000TEU of container ship MOL COMFORT got buckling at bottom plate of amidships and reached ultimate strength (ClassNK, 2014). Consequently the ship finally broke into two parts while underway from Singapore to Jeddah with a load of approximately 7,000 TEUs. According to Interim report of Committee on Large Container Ship Safety of Japanese Government (2015), the sea state at the timing of the accident had a significant wave height of 5.5m, the mean wave period of 10.3s. It also pointed out that the significant wave height might have variation from 0.5m to 2m due to the measurement errors in the weather and sea states data used for the estimation. Investigation report on structural safety of large container ships (ClassNK, 2014) concluded that the main cause of accidents as follows.
(1) Decrease of ultimate strength mainly due to lateral load by sea pressure
(2) Increase of vertical bending moment due to whipping
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