Byung-Ki Choi

Effect of Whipping on Fatigue and Extreme Loading of a 13000TEU Container Vessel in Bow Quartering Seas Based on Model Tests

Many large and ultra large container vessels have entered operation lately and more vessels will enter operation in the coming years. The operational experience is limited and one of the concerns is the additional effect of hull girder vibrations especially from whipping (bow impacts), but also from springing (resonance). Whipping contributes both to increased fatigue and extreme loading, while springing does mainly contribute to increased fatigue loading. MAIB recommended the industry to join forces to investigate the effect of whipping after MSC Napoli, a Post-Panamax container vessel, broke in two in January 2007. This has been followed up by a JIP initiated in 2008 with the following participants: HHI, DNV, BV, CeSOS and Marintek. In 2009 a new design 13000TEU vessel was tested in head seas and reported in [1]. The current paper deals with fatigue and extreme loading of the same vessel, but from realistic quartering sea conditions tested in 2010. Different headings and the effect of wave energy spreading have been investigated and compared to results from head seas. Further, the effect of the vibrations have been investigated on torsion and horizontal bending, as the model is also allowed to vibrate with realistic frequencies in other modes in addition to vertical bending. The findings suggest that changing the course is not effective to reduce the fatigue loading of critical fatigue sensitive details amidships. The effect of wave energy spreading did also not reduce the fatigue loading significantly. For the highest observed vertical bending moments in each sea state and for the three cross sections the wave energy spreading in average reduced the maxima, but for the highest sea state the effect of wave spreading did not consistently give reduced maxima. This is an important aspect when considering the available safety margin that may be reduced by whipping. The whipping gave also a considerable contribution to horizontal bending and torsion. This suggests that validation of numerical tools is urgent with respect to off head sea conditions and that these tools must incorporate the real structural behavior to confirm the importance of the response from torsional and horizontal as well as for vertical vibrations.Copyright

Time Domain Fatigue Analysis on the Upper Rolling Chock of IMO Type B Tank

IMO type B 탱크는 저온 액체 화물의 저장을 위해 선체와 독 립된 내부 화물창을 이용하는 방법으로 선체와 화물창의 직접 접 촉을 차단함으로써 저온 화물에 의한 선체의 취성화 및 외부 열 유입을 효율적으로 차단하는 개념의 화물창을 일컫는다. 그러나, 내부 화물창이 선체와 독립적으로 존재함으로 인해 선박의 운동 에 의해 야기되는 가속도 하중 등에 화물창의 이격 및 과도한 변 형이 발생할 수 있으며 이를 방지하기 위해서 화물창과 선체 간 에 별도의 연결구조를 설치하여 지지부를 구성하는 것이 일반적 이다. 화물창 지지부는 선체의 6자유도 운동에 의해 발생 가능한 화물창의 이격을 방지하는 방식으로 설계되는데, 특히 주의하여 야 할 점은 화물창의 열수축으로 인한 변형을 구속하여 과도한 열응력이 발생하지 않는 방식으로 배치되어야 한다. 선체의 상부 에는 횡동요 및 종동요에 의한 화물창의 이격을 방지하기 위한 지지부가 설치되는데 특히 횡동요의 방지를 위해 설치되는 횡동 요 초크(chock) 및 키(key)는 지속적으로 작용하는 파랑하중에 의한 피로에 취약한 부위로 알려져 있다. Fig. 1은 일반적인 초 크(chock) 및 키(key)의 형태를 보여준다. 횡동요 초크 주변의 IMO Type B 탱크 상부 Rolling Chock에 대한

Structural Design Of Ultra Large Ships Based On Direct Calculation Approach

This paper presents a project of a composite trimaran structure, designed and built for the purpose of competing at the Hydro Contest 2016 competition at Geneva Lake. Concept of the contest is to raise the awareness of tomorrow’s engineers, industrialists, opinion leaders and the general public of what is at stake with regard to energy efficiency in the sea transportation of goods and passengers, as well as to be the laboratory of tomorrow’s boats, particularly enabling the most innovative ideas to be developed in collaboration with the industrial partners. Designed boats must have technological innovations enabling them to achieve the most efficient use of energy. Therefore, the goal was to design and construct lightweight structure, within a simple closed rules, with a satisfactory stiffens and strength as well as to strive for more efficient transport, which means higher speed with minimal energy consumption. An analysis of project variants was made with regard to the hull shape, material and technology of the fabrication, and for the adopted variant a computer structure model was developed and the FEA was carried out. The structure is divided into three main sections analyzed individually: hulls, front wing and rear wing along with rudder. Calculation was made for the worst load case, i.e. mass transfer, while wings were analyzed at the highest advancing speed. The boat has structurally met all requirements since there were no structural problems in testing and competing.The trend in modern sea transportation is building of ever larger ships, which require application of different direct calculation methodologies and numerical tools to achieve their reliable structural design. This is particularly emphasized in case of ultra large container ships (ULCS), but also other ship types like bulk carriers or large LNG ships belong to this category. In this context some classification societies have developed guidelines for performing direct calculations and for that purpose there are several hydro-structure tools available around the world, mainly relying on the same theoretical assumptions, but having incorporated different numerical procedures. Such tools are mostly based on the application of the 3D potential flow theoretical models coupled with the 3D FEM structural models. This paper illustrates application of general hydro-structure tool HOMER (BV) in the assessment of ship structural response in waves. An outline of the numerical procedure based on the modal approach is given together with basic software description. Application case is 19000 TEU ULCS built in South Korean shipyard Hyundai Heavy Industries. Extensive hydroelastic analyses of the ship are performed, and here some representative results for fatigue response with linear springing influence are listed.