This paper studies the structural strength of different car Ro-Ro ships which are designed by flexible and rigid decks and subjected to symmetric loadings in the upright condition. 7800 units large PCTC has been taken as the research object, which two kinds of cargo hold FE models have been built based on flexible and rigid design of vehicle deck, by using the finite element software MSC⋅PATRAN. The FE modes are extended to 1/2 hold both in aft and fore direction on basis of 1 hold in the middle. And then, in accordance with the guidance of the Det Norske Veritas and rules of the Registro Italiano Navale apply the same load cases on both different models, to calculate and analyze the structural strength of the ships by using MSC⋅NASTRAN solver. This article explores the stress magnitude, the distribution of hotspots and the deflection deformation of main hull structure, to compare the difference between the two design concepts on the structural strength. Finally, summarizes their respective advantages and disadvantages and hopes to provide reference for the design and construction of the car Ro-Ro ships.
Car Ro-Ro ships are specially made for carrying cars or other vehicles, which belong to the category of Ro-Ro ship, divided into Pure Car Carrier and Pure Car & Truck Carrier (Zeng, 2008; Qiu,2012). Because of its high loading and unloading efficiency, large transport volume, short berth time, fast turnover rate and other characteristics, which are particularly favored by the ship-owners (Wang 2005; Wu,2016). Hull structures of the car Ro-Ro ships are different from the conventional ship. In order to facilitate auto loading and unloading, allow unimpeded access of vehicles in the cabin, the cargo areas are almost not set transverse bulkhead; the height of the strong components are restricted; the decks above the freeboard deck are almost continuous through the whole ship. This resulting in the transverse strength of the hull is mainly borne by the transverse strong frame, and the ship's stability, structural strength and unsinkability are poor.
The classification notes No.31.2 (2011) and specification part 3 chapter 1 of the Det Norske Veritas (2012) have done some introduction to the structure strength check of the car Ro-Ro ships. Lloyd's Register (2004) also gives the corresponding views on the direct strength calculation of the Ro-Ro ship. The effectiveness of longitudinal strength of multi-deck ship was verified by Zanic, V., and Andric, J. (2010) in Croatia. The guidance document GD03 (2011) of the China Classification Society provides relevant provisions on the direct calculation of the cargo area and the structural strength of the whole vessel, but does not introduce the different design concepts. Dezhuang Huang (2008) only carried out a conceptual discussion on the flexible structure of the 4900 units Ro-Ro ship. There are not many comparative studies on the Ro-Ro ships involved in different design concepts. Therefore, there is still a great deal of research space and prospect, which needs further study. This paper researches on structural strength of different car Ro-Ro ships by comparison between flexible and rigid deck designs in upright conditions, and then summarizes the advantages and disadvantages of the two kinds of design methods, hoping to provide reference for the design of Ro-Ro ships.