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Lee, Jaemin,Jo, Choonghee,Chang, Daejun,Chung, Hyun Elsevier 2018 Ocean engineering Vol.158 No.-
<P><B>Abstract</B></P> <P>This paper presents a methodology for estimating the minimum design vapor pressure of prismatic pressure vessels for on-ship application. Engineering authorities guide the codes for a novel concept design such as a prismatic pressure vessel using a design by analysis (DBA). DBA methods enable high efficiency because they directly calculate the loads to avoid inherent conservativeness that exists in a design by rule (DBR). However, in DBA methods, the designer should conduct a finite element analysis (FEA) and evaluate the results iteratively to meet the design criteria. In this paper, we propose a new approach to estimating the minimum vapor pressure of a prismatic pressure vessel that follows the design philosophy of an IMO Type C independent tank. The procedure of the proposed method was demonstrated based on a case study. An FEA was also conducted for verification purposes. The results show that the proposed method can effectively estimate the required minimum shell thickness and designed vapor pressure without conducting an iterative FEA. In addition, minimization of the tank shell thickness is made possible because the proposed method directly calculates the crack propagation rate to avoid an unnecessary margin while satisfying the fatigue crack propagation criteria.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New methodology for estimating the minimum vapor pressure of a novel concept pressure vessel is proposed. </LI> <LI> Novel pressure vessel is a prismatic pressure vessel that has high volume efficiency. </LI> <LI> Estimating the minimum design vapor pressure without conducting an iterative FEM analysis is possible. </LI> </UL> </P>
Lee, Seong-yeob,Jo, Choonghee,Pettersen, Bjørnar,Chung, Hyun,Kim, San,Chang, Daejun Elsevier 2018 Ocean engineering Vol.154 No.-
<P><B>Abstract</B></P> <P>This study proposes a pile-guided floater, a new mooring concept, for large offshore floating structures such as an offshore liquefied natural gas (LNG) bunkering terminal. The economic feasibility of the new mooring system was demonstrated through a cost–benefit analysis. The environmental loads acting on the floaters were computed using wave data at the target location. The mooring system was designed using finite element analysis to estimate the additional investment. An LNG ship-to-ship bunkering operation that included an LNG bunkering terminal, LNG carrier, LNG bunkering shuttle, and LNG receiving ship was adopted. To estimate the technical feasibility and economic benefit of the proposed mooring system, the availabilities of two types of LNG bunkering terminals were compared considering the acceptance criteria for LNG ship-to-ship transfers. One LNG bunkering terminal was a typical barge-type floater and the other was the pile-guided floater. The relative motion of the terminal with the LNG carrier and the LNG bunkering shuttle was analyzed. The limiting wave height was determined from the maximum relative vertical motion between the floaters at the position of the LNG loading arms. The availability of the pile-guided LNG bunkering terminal was significantly improved owing to the reduced vertical motion. Finally, a cost–benefit analysis verified that the new mooring concept for an offshore LNG bunkering terminal was economically feasible.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This study proposes a pile-guide mooring system for an offshore LNG bunkering terminal. </LI> <LI> The economic feasibility of the new mooring concept was demonstrated through a cost-benefit analysis. </LI> <LI> The relative vertical motion of the floating bodies was analyzed to evaluate availability of LNG ship-to-ship transfer. </LI> <LI> Availability of the pile-guided LNG bunkering terminal was significantly improved by the cost-effective mooring structure. </LI> </UL> </P>
Lee, Seong-yeob,Jo, Choonghee,Chang, Daejun Elsevier 2019 Marine structures Vol.64 No.-
<P><B>Abstract</B></P> <P>This study proposed a decision procedure to determine an optimal set of component reliabilities to satisfy the system target reliability with a minimum investment. The relationships between the initial costs and reliability were studied for each structural component to establish an objective function. Finite element analysis and Monte Carlo simulations were performed in order to set the relationships. The system configuration and target reliability of the structural system were used as the inequality constraint of the optimization process to maintain its safety level. A pile-guide mooring system (PGMS), a new mooring concept for an offshore liquefied natural gas bunkering terminal, was considered as a case study. The PGMS was modeled as a series system combining <I>k</I>-out-of-<I>n</I> components to consider the redundant parts. Finally, the proposed method determined the optimal number of guide-piles, redundant parts, and an optimal combination of component target reliabilities for the PGMS.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An optimization problem was defined to determine an optimal set of component target reliabilities with the cost minimized. </LI> <LI> Investment and component reliability were analyzed based on finite element model and Monte Carlo simulation. </LI> <LI> The balanced set of component reliabilities were economical enough for series system of high-reliability only. </LI> <LI> The unbalanced set of component reliabilities were advantageous for pile-guide mooring system. </LI> </UL> </P>