RIASSUNTO
ABSTRACT
The objective of the present study is to assess the ultimate hull girder strength taking the section modulus into account under longitudinal bending. A Ro-Ro Ship is taken as object ship. A Ro-Ro Ship has a unique character because most of the longitudinal elements locate above neutral axis. While there are not the longitudinal elements under the neutral axis particularly at the bottom part so that the bottom part consists plate only. The simple expression implemented into in-house program to calculate the section modulus of ship cross section is performed. The cross section is assumed to be remained plane and the simply supported of boundary condition is imposed on plate and stiffened plate elements in the cross section. The vertical bending moments are imposed to both sides of the cross section. The ultimate hull girder strength is calculated by considering the section modulus including their progressive collapse behavior for Ro-Ro ship hull.
INTRODUCTION
The Ro-Ro ship is one of the ship types which transport the cargo in horizontal direction and eliminate the need for onboard or deckside lift-on and/or lift off instrument. The Ro-Ro ship has been innovated to carry processed forest product, lumber, playwood, cars and many things. Ro-Ros are an imprortant connection for the intermodal transportation network. In this regard, the section modulus could be one of the important parameters from the viewpoint of assessing the ultimate strength of all the decks on which cars, passengers and so on are put. In spite of human error, the structural degradation during loading and unloading gives impact to the ultimate strength of ship's hull.
The ultimate hull girder strength of merchant ships including Ro-Ro ship has been assessed by some researchers. Kukkanen, T and Matusiak, J (2014) presented the numerical and experimental results of nonlinear wave loads. A nonlinear time domain method had been developed and the theoretical background of the method were provided. The method was based on the source formulation expressed by means of the transient three-dimensional Green function. The time derivative of the velocity potential in Bernoulli's equation was solved with similar source formulation to that of the perturbation velocity potential. Korkut, E et al (2005) carried out measurements of global loads acting on a Ro-Ro model in regular waves for intact and damaged conditions. The stationary model was tested in different wave heights and wave frequencies for the head, beam and stern quartering seas in order to explore the effect of damages and wave heights on the global loads acting on the model. The analysis of the result indicated that the damages had an adverse effect on the loading conditions on the model depending upon the directionality of the waves and frequency range applied. This effect might cause structural damage on the ship and danger the safety of the ship and passenger on board. Kim, D.H and Paik, J.K (2017) developed a fully automated methodology for the optimum design of hull structural scantlings for merchant cargo ships that were modelled by plate-shell finite elements. A full optimization technique with multi-objectives was applied for minimizing structural weight and maximizing structural safety, as per design constraints associated with the ultimate limit states of the plate panels, support members and hull girders. The developed procedure was applied to the hull structural scantlings of a very large crude oil carrier (VLCC), and the test demonstrated the procedure's capacity to meet the strength requirements of common structural rules. Muis Alie, M.Z et al (2016) investigate the influence of superstructure on the longitudinal ultimate strength of a Ro-Ro ship. To investigate the ultimate strength, the Smith's method was adopted and implemented into the thin-walled beam. The cross section of Ro-Ro ship was taken to be analyzed. Muis Alie, M.Z et al (2017) assessed the ultimate hull girder strength of Ro- Ro ship after damaged. The cross section of Ro-Ro was taken to be analyzed. The collision and grounding damages were assumed to be placed on the side and bottom area. The damages were created by removing the element from the side shell and bottom parts. Finally, the result obtained was compared with one another. Also, the progressive collapse analysis of ship hull girder based on Smith's method was developed by Yao and Nikolov (1992). Naar, H et al (2004) described a couple beam method, which estimate elastic response in the longitudinal bending of a passenger ship with a large multi-deck superstructure. The method could be applied during an early project stage, when detailed three-dimensional finite element modelling was not yet possible. The theory was based on assumption that each deck in the superstructure and also the main hull could be considered as thin-walled beam.