Graduate School of Nihon University Chiba, JAPAN

arita@aquarius.ocean.cst.nihon-u.ac.jp

　

The designing water depth of a very large floating structure is about 20-30 m, and the limit of depth is 50 meters. This condition determined by the designing water depth of a breakwater. Some studies suggested that the breakwater putting into the reduction devices of hydroelastic deformation. Some of anti motion devices for a very large floating structure have been proposed. In this study we suggested an example of analysis method that calculate hydroelastic deformation of a very large floating structure attached the vertical plates at weather side of floating body.

　

This study based the three-dimensional singular point distribution method. A hydrodynamics and an elastic deformation carried out using by modal analysis. The modal of structure carried out application software (MSC. Nastran for Windows).

　

In the results, we suggested the method of the hydroelastic deformation of a very large floating structure attached the vertical plates.

　

　

Graduate School of Nihon University Funabashi, Chiba, JAPAN

asanuma@aquarius.ocean.cst.nihon-u.ac.jp

　

It is well known that in single point mooring 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. 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 study, 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. Finally, a new mathematical model is proposed to describe the current forces acting on FPSO.

　

　

Nihon University Chiba, JAPAN

ikoma@ocean.cst.nihon-u.ac.jp

　

A large aircushion-supported type can be considered for a very large floating structure. The metacenter height of such the floating type becomes low. However, there is no problem because the length and the breadth of a very large floating structure are effectively too long against wavelengths of ocean waves. Therefore, there is few possibility of the capsizal.

　

This paper shows the two prediction methods for the analysis of hydrodynamic forces on an aircushion-supported elastic floating structure. One is an approximate method in which the zero draft is assumed, and the pressure distribution method is applied. Therefore, the problem becomes to two-dimensional horizontally. Another one applies the three-dimensional source distribution method. There are some areas being a free water surface in the aircushions. A behavior of the free surface in the aircushion is directly considered in the analysis of the water pressures or the velocity potentials.

　

In the results, the validity of the zero draft assumption is proved. In addition, a characteristic of the elastic deformation is discussed in head sea conditions. It is found that the elastic deformation is little and the heave motion mode becomes very small when a whole bottom of the floating structure is the aircushion. However, when structural surfaces at the bottom are wide, i.e. not air-supported areas are large, there are some case that the deformation increases because of the resonance phenomenon.

　

Then, we will investigate the water wave behavior in the aircushion and around the floating structure. From the wave behaviors, we will examine the wave drifting forces.

　

　

Nihon University Funabashi, Chiba, JAPAN

k21006@ocean.cst.nihon-u.ac.jp

　

In recent years, the study which applies the numerical calculation for a nonlinear wave to the design of a marine structure is progressing. The one VOF (Volume Of Fluid) method is that applicability is high for the strongly nonlinear phenomenon. The VOF method is used for expression on the complicated free surface, such as wave breaking and wave overtopping. And it is clear that those phenomenon are calculable with high accuracy. Also about the floating structure, application of the VOF method to a phenomenon with the difficult prediction by linear wave analysis, such as wave overtopping by motion of floating breakwater at the stormy weather and movement of a mooring anchor, is expected. Then, in this study, the numerical wave analysis program which used the VOF method was developed, and this was applied to the wave field analysis around the floating body. The object of calculation is a penetration wave, a reflective wave and a wave power when an incident wave acts on fixed floating body. And comparison with an analysis result and a hydraulics model experiment showed the validity.

　

Consequently, it was shown that the duplication wave of the incident wave and the reflective wave, phase difference between the incident wave and the penetration wave and the transfer waveform can reappear with sufficient accuracy. Moreover, the calculation result and the experiment result are mostly in agreement also about wave power, so the validity of this analysis result is shown.

　

　

Nippon Kaiji Kyokai (ClassNK)

Chiba, JAPAN

　

Floating Production, Storage and Offloading Systems (FPSOs) have been widely used in oil industries in recent years. The term 'FPSOs' covers considerably wide range of floating structures in terms of mobility/immobility, methods of survey and maintenance, etc. One of the practical and economical ways to construct FPSOs is a conversion from oil tankers, of which single hull tanker should be phasing out by recently introduced international requirements. In this context, FPSOs newly constructed or converted will be built to the design/operation specification for being engaged in services at the specific site so that the double hull requirement need not be complied with.

　

Nevertheless thus there is a big difference in design principle between the floating structures of mobility and immobility, the usual regulations for FPSOs have been biased to their mobility. In this paper, the design principle/concepts and technical views of new guidelines intended for site-specific FPSOs developed by ClassNK are introduced. ClassNK has also established requirements for longer service lives, taking into consideration the survey scheme without dry-docking and corrosion margin depending on service lives in line with the new design/operation concept. Furthermore fatigue design criteria is explicitly described referring to the latest developed rules that might enable designer to take into account the effects of time dependent mean stress when considering cyclic stress.

　

Finally some topics such as prescriptive rule versus risk-based rule as well as risk-based inspection are discussed in order to foresee the future trend of regulations and rules regarding FPSOs.