It is well known that in single point mooring or anchoring the slowly varying oscillation of a ship is caused by action of current and wind. During the slowly varying oscillation, extraordinary tension occurs in the mooring line when the ship’s yaw angle becomes nearly maximum, and incurs, as the case may be, in breakdown of mooring lines or unforeseen drift of anchors. Floating Production, Storage and Offloading (FPSO) systems are often moored as Single Point Mooring (SPM) systems. SPM systems can be Catenary Anchor Leg Mooring (CALM) systems or Single Anchor Leg Mooring (SALM) systems. It has been required to predict and evaluate performance of horizontal plane behavior of FPSO in current, wind and waves, since the workability and safety of FPSO become important from the stand point of the Life Cycle Engineering. Numerical simulation is one of the practical methods for prediction of FPSO performance and it needs quite accurate values of hydrodynamic coefficients in the mathematical model. Recently some attempts on improvement of accuracy in prediction of the hydrodynamic coefficients were made and approximate formulae for hydrodynamic derivatives including the interaction effect of main hull form and appendages were also proposed. Recently extensive studies for numerical models which describe components of hull, propeller, rudder, thruster, wind and waves separately, and these interactions have been made successively. In this paper, first, the basic equations of maneuvering motion are explained. And, an estimation method of slender body theory for hydrodynamic force acting on the hull is outlined. The authors explain numerical models to obtain FPSO coefficients for the horizontal plane behavior from mathematical model of ship maneuverability. And, numerical test of FPSO under the slowly varying oscillation is carried out. Finally, a new mathematical model is proposed to describe the current forces acting on FPSO under the slowly varying oscillation.

The authors started this research on estimation method of responses for floating structures using Computational Fluid Dynamics (CFD). This paper is first step, which has potential to be very valuable to the engineering community. The numerical method used in this study is the Moving Particle Semi-implicit (MPS) method 1) 2), which is based on particles and their interactions. MPS method that was developed recently is one of particle method. The particle number density is implicitly required to be constant to satisfy incompressibility. A semi-implicit algorithm is used to for two dimensional incompressible non-viscous flow analysis. The particles whose particle number densities are below a set point are considered as on the free surface. In this paper, first, the authors explain the outline of MPS method that Kshizuka et al. developed. You can see more details of this method by references. And the calculation test of column collapse problem is carried out to check our code that we developed. Second, the modeling of free surfaces is explained. And the authors proposed the way to skip irregular data of wave height. Validation of wave profiles was carried out comparing Stokes theory. Third, calculation results of floating body are showed. This method of calculating response of floating structure is by Koshizuka et al. 3). Finally, the authors show calculation results of wave exciting forces by MPS method comparing singular point distribution method (SDM).

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MPSO, mono-column hull type FPSO, is attracting the interest as a floating production system which has high performance for motion and large tank capacity in recent years. The authors had performed a mooring system safety evaluation of a MPSO named ‘MONOBR’ which was assumed to be installed at the Gulf of Mexico in the international collaborative research and development project between PETROBRAS and JOGMEC. There exists a strong current called the Loop current in the Gulf of Mexico. It is known that cylindrical floaters like SPARs or MPSOs sway with the long period and large amplitude in the transverse direction of the current. The motion is called Vortex Induced Motion (VIM), and is caused by vortex shedding from the sidewall of the floater. VIM is one of the important issues in the safety evaluation of mooring system of MPSO. Generally, the combined environmental conditions in which wind, waves and current exist are concerned for the safety evaluation of mooring systems. Therefore, it needs to estimate VIM in waves and current. The authors had performed the VIM measurement tests in order to investigate the estimation method of VIM in waves and current. The results of the VIM measurement test in waves and current and the results of the mooring safety evaluation method using the estimation method of VIM in waves and current are described in this paper.

SummaryRecently, the natural gas is expected to be an environmentally friendlier energy and alternative to the nuclear energy. In the social situation, many oil and gas and engineering companies had studied FEEDs of the FLNG expected to be a new production system for offshore natural gas development in the near future. The FLNG system is no proven technology and there is no operation, which can make it difficult for us to design the FLNG. Furthermore, it is noted that the FLNG designers can't get enough information for the design and need the design standard.Gas explosion is the technical problems for the topside facilities of FLNG. Though it is so difficult for us to understand the gas explosion phenomenon, the FLNG designers have to evaluate the peak over pressure of gas explosion for the design of topside layout to prevent gas explosion from damaging the facilities.The objective of this paper is to study the gas explosion by the numerical simulation. We have conducted the gas explosion analysis for FLNG model by the numerical simulation program AutoReaGas which was developed by TNO and the Century Dynamics. The results show that the physical factors such as ignition location can make significant effects on the peak over pressure of gas explosion.