Agbami FPSO is a floating facility for production, storage and offloading of oil at OPL 216/217 offshore Nigeria of the central Niger delta. The FPSO is positioned with spread moorings in water depth of about 1500 m for the service life of 20 years. As per the design requirement, the hull of FPSO shall be designed to meet ABS’s SFA (Spectral Fatigue Analysis) notation and the seagoing condition. Seagoing is a mandatory condition additionally required by Client, assuming a navigating vessel of North Atlantic. But, to conservatively assess Agbami for 60 years at its Onsite except specific details was taken into account, which is related to the uncertainties in S-N data & Palmgren-Miner’s damage rule and etc. Normally the off-western Nigerian sea has swell-governed environment and the multi-peaked spectral characteristics with wave and swells. For the spectral fatigue analysis, Jonswap spectrum for wind wave & Gaussian spectra for swells were taken into consideration as a representative in case of Onsite. Thus, in order to achieve a single damage, the combined spectral method for Onsite was introduced on the basis of EMDC’s FPSO FMS (Fatigue Methodology Specification). On the contrary, Walden’s wave scatter diagram as recommended by ABS for Seagoing was applied. The forward speed of FPSO in Seagoing case was also taken into account by WASIM, a hydrodynamic tool of DNV and compared to the results of PRECAL, ABS’s hydrodynamic code to ensure the validity of the analysis. The post-process to calculate fatigue damage was carried out using the in-house program to analyze fatigue of FPSO. The results from the analyses were found that the Seagoing led consequentially critical fatigue damage for most of hull structures more than Onsite that has moderated sea state.

This work is motivated by the need to identify the fire and explosion risk on LNGCs developed by Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME) because the main engines are designed to use highly pressurized natural gas (about 300 bar), which has caused vague fears of fire and explosion risks. In this context, to identify the risk of fires and explosions quantitatively caused by ignitions of unintended leaked gas from fuel gas lines, a FERA was carried out for the LNGCs [1]. This paper, as a part of the FERA, presents the results of a preliminary investigation on the effect of introducing the highly pressured fuel gas system into LNGCs on the fire and explosion risk especially in the cargo compressor room. This study is conducted in a comparative way considering the risk contribution of each parameter that could impact on the fire and explosion risk in LNGCs. The effect of the highly pressured fuel gas is indirectly taken into account by the change of the initial leak rate in the system. To identify effects of the considered parameters quantitatively, dozens of simulations for the selected gas dispersion, explosion and fire scenarios were carried out using FLACS and KFX. Based on the results from the simulations, it is concluded that, in case of the LNGCs, the effects of the initial large leak rate due to the high pressure in the fuel gas pipes on fire and explosion risk are not significant compared with the other parameters’ effects.

No abstract

This work is motivated by the need to identify the fire and explosion risk on liquefied natural gas carriers (LNGCs) developed by Daewoo Shipbuilding & Marine Engineering Co., Ltd., because the main engines are designed to use highly pressurized natural gas (about 300 bar), which has caused vague fears of fire and explosion risks. In this context, to identify the risk of fires and explosions quantitatively, a fire and explosion risk analysis (FERA) was carried out for the LNGCs. This paper, as a part of the FERA, presents the results of a preliminary investigation on the effect of introducing the highly pressured fuel gas system into LNGCs on the fire and explosion risk especially in the cargo compressor room. This study is conducted in a comparative way considering the risk contribution of each parameter that could impact on the fire and explosion risk. The effect of the highly pressured fuel gas is indirectly taken into account by the change of the initial leak rate in the system. To identify effects of the considered parameters quantitatively, dozens of simulations for the selected gas dispersion, explosion, and fire scenarios were carried out using FLACS and KFX. Based on the simulation results, it is concluded that, in case of the LNGCs, the effects of the initial large leak rate due to the high pressure in the fuel gas pipes on the fire and explosion risk are not significant compared with the effects of other parameters such as leak amount, leak location, and leak direction.

The aim of this study is to investigate methods of assessing the turbulence effect for the helideck availability study. Due to the limited space on offshore platforms, a helideck is normally positioned on cramped areas and this makes turbulence flows around the helideck. CAP 437, the representative standard for the offshore helideck design suggests various criteria for the helideck availability assessment and recommends a Standard Deviation of Vertical airflow Velocity (SDVV) value to be used for the turbulence effect assessment. Although there is a specific value of SDVV recommended in CAP 437, different interpretations are possible in the calculation of the value resulting in totally different assessment outcomes even under the same analysis condition. In this study, two different approaches are investigated and their results are compared. One approach is based on the spatial variation of the mean vertical velocity while the other utilizes the Turbulence Kinetic Energy (TKE) value from the Computational Fluid Dynamics (CFD) simulation. With a CFD tool, Kamelon FireEX (KFX), a couple of 3-dimensional simulations is performed and turbulence flows around an offshore semi-rig are obtained. SDVV values are calculated using both approaches and compared each other as well as with criteria recommended in CAP 437. It is hoped that the result of this study is helpful to engineers for understanding evaluation methods of turbulence effects in the helideck availability assessment.