• International Journal of Naval Architecture and Ocean Engineering
• /
• v.12 no.1
• /
• pp.723-732
• /
• 2020

A theoretical calculation model for ship stern bearings with large hull deformation is established and validated theoretically and experimentally. A hull simulation model is established to calculate hull deformations corresponding to the reaction force of stern bearings under multi-factor and multi-operating conditions. The results show that in the condition of wave load, hull deformation shows randomness; the aft stern tube bearing load obeys the Gaussian distribution and its value increases significantly compared with the load under static, and the probability of aft stern tube bearing load greater than 1 is 65.7%. The influence laws and levels between hull deformation and bearing reaction force are revealed, and suggestions for ship stern bearing specifications are proffered accordingly.

• Journal of the Society of Naval Architects of Korea
• /
• v.48 no.6
• /
• pp.509-515
• /
• 2011

The radar cross section (RCS) of warships is a crucial design factor to improve the survivability in terms of not only low observablity of the platform but also efficiency of on-board sensors and jamming devices against enemy threat. In design stage, numerical models are generated in order to quantitatively assess RCS, of which hull surfaces are modeled with the finite number of the flat plate. However, in practice, hull surfaces are permanently deformed by various kinds of loads such as winds and ocean waves faced during operations. In this paper, the effect of these shell plate deformation to RCS is numerically investigated. For this purpose, RCS calculations are carried out for various kinds of numerical models, such as single plates, dihedrals, large-sized undulate plates, and virtual warships, with some extent of permanent deformation. The results are compared with those of corresponding models without permanent deformation. It is concluded that the permanent deformation of hull surface highly influences RCS characteristics of warships, therefore they should be considered in the RCS analysis.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.5
• /
• pp.389-395
• /
• 2019

Turret mooring type Floating Production Storage and Offloading (FPSO) is designed to rotate the hull around a turret system. The system is mounted inside a cylindrical moon-pool structure of the ship hull structure. The upper part of the moon-pool structure called Bogie Support Structure (BSS) is supported on ring type rail structure (bogie), so high roundness is required at the top of the structure. In this study, the deformation measured during BSS installation was compared with the predicted values through the thermal elasto-plastic analysis, and the causes of deformation were analyzed. Deformation behavior of cylindrical structure with a very large diameter compared to the thickness was investigated. In addition, a proper welding sequence and correction method for the deformed structure were proposed. This study can be an example of the solution to the tolerance problem of large cylindrical structures.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.2
• /
• pp.55-60
• /
• 2004

This paper describes the estimation method of hull girder response of ships due to springing. To this aim, nonlinear springing effect on the hull girder is evaluated including vertical, horizontal, and torsional deformation of the hull. The Timoshenko beam model is used to calculate the stress distribution on the hull girder. The quadratic strip method is employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, 'rigid lid'is adopted on the hull free surface level and hydrodynamic coefficients are interpolated for asymptotic values. The results of example calculation show a reasonable agreement with previous results for both symmetric and anti-symmetric responses.

• Journal of the Society of Naval Architects of Korea
• /
• v.36 no.4
• /
• pp.116-127
• /
• 1999

Line heating is a method widely used in forming ship hull surface. From the viewpoint of mechanics it is large deformation thermal elasto-plastic problem of arbitrary shaped plate. Many researches have been carried out to resolve this problem. Especially, Jang et al.[1] proposed a simplified thermal elasto-plastic analysis method to predict effectively the deformation of plate due to line heating. In this paper, we improved the method of Jang et al.[1] by considering tension yielding in temperature decreasing stage and verified with experimental results. FEA program using MITC4 degenerated shell element was made to deal with elastic large deformation problem. The newly proposed method can be used in the simulation and control of forming hull surface for higher productivity with simplicity and efficiency.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2006.11a
• /
• pp.201-204
• /
• 2006

A three-dimensional finite element (FEM) model has been developed to simulate the deformation due to bead on plate welding of curved plates with curvature in the weld direction. By using traditional method such as thermal-elastic-plastic FEM, the weld-induced deformation can be predicted accurately. However, this method is not practical approach to analyze the deformation of large and complex structures such as ship hull structures in view of time and cost. This study is classified from the aspect of equivalent load based on inherent strain near the weld line. Therefore, the residual deformation can be simply computed by elastic analysis. Further more, a practical solution is proposed to consider the contact between the plate and the positioning jig by judging the reaction forces of the jig at calculation step and the effect of the longitudinal curvature is closely considered.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.158-161
• /
• 2008

In the line array roll set (LARS) process, the initial plate is progressed into the final shape in a stepwise or pathwise manner according to the basic principle of the incremental forming process. The deformation proceeds simultaneously in the longitudinal and transverse directions. It was found that the curvature level of the formed plates in the previous study was well over the curvature required in shipyards. This fact shows that the LARS method has considerable potential for shipbuilding applications. In this study, several experiments with the LARS system is carried out fur manufacturing of plates with large curvatures. The bulbs at a stem and stern among ship hull plates correspond to these plates. Furthermore, the qualities of formed plates are evaluated according to the types of roll arrangements through experimental and numerical analyses.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.8
• /
• pp.4717-4722
• /
• 2014

In shipyards, a large number of dog-pieces are used to align welding joints and prevent welding deformation in the block assembly stage. The huge working man-hours consumed in the working process of dog-pieces impedes the productivity growth of shipyards. In this study, an analysis method based on the experimental results was proposed to simulate the welding deformation of butt joints with a dog-piece setting. The simulation of welding deformation of a hull block joint was performed using the proposed analysis method. Finally, the proposed analysis method can be used to establish guidelines for the proper use of dog- pieces in the block assembly stage.

• Special Issue of the Society of Naval Architects of Korea
• /
• 2005.06a
• /
• pp.138-143
• /
• 2005

Recently, it is much more required to approach the accurate shaft alignment analysis according to the tendency of active showing in large container vessel and that of the heavy weight of propeller in connection with it. Shaft alignment calculation lies upon how the pressure apply on bearings properly in operation of main engine and how the stress of shaft puts within that of limit of bearing material and how the movement of shaft is prospected owing to propeller forces and moments. Therefore, we have conducted the shaft alignment calculation of very large container vessel considering the deformation of hull structure and the propeller forces and moments and the static and dynamic condition of shaft. The calculation results show the pressure distribution of aft bush and the movement of shaft in bearing. The shaft alignment calculation helps the stable application of shaft alignment, which was proved in sea trial.

• Special Issue of the Society of Naval Architects of Korea
• /
• 2008.09a
• /
• pp.46-53
• /
• 2008

Recently, the synthetic material stern tube bush has been applied by ship owner's requirement because the synthetic material has a merit. That is to say, when stern tube seal is damaged and sea water comes into stern tube, it can work without problem because of water lubricating property. However, the material also has a demerit of temperature rise problem when some factors meets on synthetic material, for example, not sufficient lubrication oil supply and not proper shaft alignment and so on. As known in the world, the RAILKO bush is rampant for synthetic material by some ship owner because of the above mentioned reason. However, the bush has several accidents on large container vessel. Unfortunately or fortunately our yard has a chance to apply the RAILKO bush owing to requirement of specific ship owner. Therefore, it is much more required to approach the accurate shaft alignment analysis. In line with this reason, we had a shaft alignment calculation considering hull deformation and hull flexibility (hull stiffness). Also, in the calculation, we had considered dynamic condition which is reflected he propeller thrust forces and moments and oil film stiffness on the shaft alignment calculation. According to he shaft alignment calculation, bearing slope was applied on the tern tube bush and was measured. The RAILKO bush should be applied the running in procedure according to maker's recommendation for performing the oil film on the bush surface. Finally, the vessels were delivered successfully without any problem with AILKO bush as shown on his paper.