The stability of FPSO or offloading shuttle tanker may be affected in wave conditions which excite parametric rolling. The offloading operations are thereby ceased and eventually leads to loss in production which affects the revenue of global production, better known as downtime cost. This paper discusses downtime cost analysis of offloading operations due to parametric rolling of shuttle tanker under regular waves in Malaysian waters for three different locations. The downtime due to parametric rolling is investigated for two different water depths for which the probability of occurrence was calculated from the location specific wave scatter diagram. The results of parametric rolling of shuttle tanker along with downtime cost charts are presented. Additionally, a Graphical User Interface (GUI) was developed and its work procedure is demonstrated in this paper. The down-time cost calculator will help the oil operator companies to analyze the economic risks involved for field developments and anticipate the loss in revenue for downtime occurrences. The developed GUI was copyrighted under literary work as intellectual property.
The numerous ship accidents at sea have usually resulted in tremendous loss and casualties. To prevent such disastrous accidents, a comprehensive investigation into reliable prediction of seakeeping performance of a ship is necessarily required. This paper presents computational fluid dynamics (CFD) analysis on seakeeping performance of a training ship (full scale model) quantified through a Response of Amplitude Operators (RAO) for heave and pitch motions. The effects of wavelengths, wave directions and ship forward velocities have been accordingly taken into account. In general, the results revealed that the shorter wavelengths (l/L ? 1.0) have insignificant effect to the heave and pitch motions performance of the training ship, which means that the ship has good seakeeping behavior. However, the further increase of wavelength was proportional with the increase of RAO for her heave and pitch motions; whilst it may lead to degrade her seakeeping quality. In addition, the vertical motions behavior in the following-seas dealt with higher RAO as compared with case of the head-seas condition. Similarly, the subsequent increase of the ship forward velocity was prone to relatively increase of the RAO for her heave and pitch motions especially at l/L ? 2.0. It was merely concluded that this seakeeping prediction using CFD approach provides useful outcomes in the preliminary design stage for safety assessment of the training ship navigation during sailing.
Abstract. Designing a fixed offshore jacket platform requires the approximation of wave forces acting on jacket members which is influenced by multiple factors such as wave height, wave period, shape and size of the jacket member. An important part of determining wave forces using Morrison's equation is the accurate determination of hydrodynamic coefficients. The presence of sacrificial anodes increases the hydrodynamic coefficient of jacket member and therefore this research focuses on improving the design of fixed offshore platforms by conducting experimental investigation on rigid cylinders in order to obtaining better estimates for hydrodynamic coefficients. Steel members of size 27 and 34mm diameters were tested in the wave basin 20 m x 10 m x 1 m. Different set of regular waves with varying height and frequency were generated. Clean members were fitted with small welded steel bars of fixed length and size along the member simulating sacrificial anodes. The results show that the coefficients obtained were close to the values proposed by PTS and API standards but are generally lower than the suggested value of 2.0 for both Cd and Cm.
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