Moon Pool Research Articles

Analysis of heave motions of a truss spar platform with semi-closed moon pool

This paper presents the heave motion of a truss Spar platform in regular waves considering the dynamic coupling between the motions of the platform and water in the moon pool. For a spar platform with semi-closed moon pool, water can flow freely through the guide plate at bottom of the moon pool. The mass of water inside the moon pool is comparable to the platform mass itself if the top tension riser system is used. Then the effect of the moon pool water on the motions of the platform should not be ignored. In the study presented in the paper, a 2-DOF (Degree of Freedom) dynamic coupling equations of the heave motions of the spar platform and the vertical motions of water in the moon pool were derived considering that the moon pool is totally closed, or 30% or 70% open. The results show that motions of water in the moon pool significantly affect the heave motions of the spar platform. Parametric study was also carried out to find the effect of the ratio of opening of the bottom plate on the coupled motions. Finally the model experiments were carried out to validate the numerical calculations.

Analyses and countermeasures of deepwater drilling riser grounding accidents under typhoon conditions

Abstract For deepwater drilling riser system facing grounding risk in the South China Sea, a mechanical analysis model of deepwater drilling riser grounding accident was established. Focusing on drilling riser grounding accidents of a deepwater floating drilling platform in the South China Sea, mechanical characteristics and grounding accidents of riser were analyzed. And the riser retrieving window was determined. The results showed that the shape of the riser system after riser grounding is catenary. The maximums of bending moment and von Mises stress are located at lower flex joint. Platform moon pool, tensioner and lower flex joint are damaged due to severe bending deformation in the upper and lower drilling riser system after riser grounding accidents. The riser may fracture if drilling platform continues to move toward shallow water. Drilling platform displacement and riser lift height must be within the riser operation window during riser retrieving, or else the riser may fracture and the LMRP may suffer further damage. Residual riser and LMRP can be retrieved in a fixed position when the drilling riser system is separated from seabed.

내부가 빈 원기둥의 수직운동 특성

In the present investigation, the hydrodynamic characteristics of a vertically floating hollow cylinder in regular waves have been studied. The potential theory for solving the diffraction and radiation problem was employed by assuming that the heave response motion was linear. By using the matched eigenfunction expansion method, the characteristics of the exciting forces, hydrodynamic coefficients, and heave motion responses were investigated with various system parameters such as the radius and draft of a hollow cylinder. In the present analytical model, two resonances are identified: the system resonance of a hollow cylinder and the piston-mode resonance in the confined inner fluid region. The piston resonance mode is especially important in the motion response of a hollow circular cylinder. In many cases, the heave response at the piston resonance mode is large, and its resonant frequency can be predicted using the empirical formula of Fukuda (1977). The present design tool can be applied to analyze the motion response of a spar offshore structure with a moon pool.

Wave radiation and diffraction by a two-dimensional floating body with an opening near a side wall

The radiation and diffraction problem of a two-dimensional rectangular body with an opening floating on a semi-infinite fluid domain of finite water depth is analysed based on the linearized velocity potential theory through an analytical solution procedure. The expressions for potentials are obtained by the method of variation separation, in which the unknown coefficients are determined by the boundary condition and matching requirement on the interface. The effects of the position of the hole and the gap between the body and side wall on hydrodynamic characteristics are investigated. Some resonance is observed like piston motion in a moon pool and sloshing in a closed tank because of the existence of restricted fluid domains.

Radiation and diffraction analysis of a cylindrical body with a moon pool

An analytical solution is presented for the radiation and the diffraction of a cylindrical body with a moon pool floating on the surface of water with a finite depth. The expressions for the potentials are obtained by the method of separation of variables, and the unknown coefficients are determined by the boundary conditions and the matching requirements on the interface. The effects of the moon pool on the hydrodynamic characteristics of the body are investigated. Some peaks are observed on the curves of the added mass and damping coefficients, corresponding to the resonant frequencies of the moon pool. The internal free surface moves like a piston at a certain low resonant frequency.

Drilling for microbes

For scientists who study subseafloor sediment, it’s not unusual to spend a lot of time at sea aboard a ship with a gaping hole in its hull. Known as a moon pool, the hole serves as a portal for the ship’s weighty drilling equipment to retrieve core samples of seafloor sediment thousands of meters below. Aboard …

Experiments to determine thruster design parameters of a moored floating platform

Control devices are selected in the preliminary design stage of any large platforms. This is true for deciding fin area for roll/pitch control of moving platform and thruster sizes and numbers for maneuvering assistance in the case of very low speed conditions. For moored platform the excursions are to be determined to activate the thruster system to reduce the line tension. In the case of a drill ship with moonpool there are some additional parameters of interaction. To some extent the parameters can be contained by optimizing the size and shapes of moon pools on board ships. The dynamics of a moored platform fitted with moon pool are determined here. Such responses are necessary to arrive at the actual sizes and numbers of thrusters to keep the vessel within the tolerances of excursion for ease and accurate operations.

FPSO Moon Pool 구조의 용접변형과 잔류응력에 관한 연구

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper presents the simulation of welding-induced residual stress analysis to examine the cause of cracking in the SUS-overlay welding specimen at FPSO Moon Pool structure.

FPSO Moon Pool 구조에서 발생되는 용접 잔류응력에 관한 연구

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper presents the simulation of welding-induced residual stress analysis to examine the cause of cracking in the SUS-overlay welding specimen at FPSO Moon Pool structure.

문풀을 가지는 2차원 부유체의 강제 상하동요에 대한 CFD 해석

A two-dimensional floating body with a moon pool under forced heave motion, including a piston mode, is numerically simulated. A dynamic CFD simulation is carried out to thoroughly investigate the flow field around a two-dimensional moon pool over various heaving frequencies. The numerical results are compared with experimental results and a linear potential program by Faltinsen et al. (2007). The effects of vortex shedding and viscosity are investigated by changing the corner shapes of the floating body and solving the Euler equation, respectively. The flow fields, including the velocity, vorticity, and pressure fields, are discussed to understand and determine the mechanisms of wave elevation, damping, and sway force.

수치 파동 수조를 이용한 부유체의 문풀 (Moon Pool) 유동해석

The aim of this study is to analyze the hydrodynamic properties of a 2D floating body with moon pool using a 2D fully nonlinear Numerical Wave Tank(NWT). This NWT was developed based on the Boundary Element Method(BEM) with potential theory and fully nonlinear free surface boundary conditions. Free surface elevations in the moon pool were calculated in the time domain for various frequencies of forced body motions. The added-mass and damping coefficients of the heaving body were also obtained. The present numerical results were compared with the analytic and experimental results and their accuracy was verified.

Preparatory Tests with an Explorer Class Autonomous Underwater Vehicle for Missions under Sea Ice

The autonomous underwater vehicle (AUV) operations described here are preparatory missions to enable operation of an AUV under sea ice in polar regions. The proposed polar projects include operations under land fast ice in the Arctic through an ice moon pool and a planned project to assess sea ice mass balance and habitat assessment in the Southern Ocean in East Antarctica. This paper focuses on the preparatory missions, done in open water, and the planned Southern Ocean project. The plan is to use an autonomous underwater vehicle (AUV) for the under ice component of measurements. The ultimate goals are to quantify the size and shape of ridge keel structures and their contribution to the sea ice mass balance over a study region; to understand the processes that link sea ice with the distribution of ice algae and krill; to provide the necessary field measurements, over sufficiently large areas, for the calibration/validation of satellite and aircraft-based measurements of the sea ice and snow cover thickness; and to provide baseline measurements of sea ice thickness for future climate monitoring.

Radiation and Diffraction Analysis of the McIver Toroid

A hydrodynamic analysis is performed of a special toroidal body which is known to have a nontrivial solution of the homogeneous linearized free-surface boundary-value problem with oscillatory time- dependence. This solution corresponds physically to unbounded resonant motion of the fluid in the 'moon pool' at the center of the toroid. The added mass, damping, and elevation of the free surface in the moon pool are computed for a range of wavenumbers, with singular results in the resonant regime.

The Development of a Low Motion Floater and The Application to The Floating Crude Oil Production System

New concepts of hull forms with characteristics of low motions in waves, a big displacement and simple hull structure have been developed. They are most ideal for the floating production, storage and offloading units (FPSO). Two new concepts, a mono-column type (MC type) and a double moon pool type (DM type) were introduced in the former paper read at OMAE (1989).This paper will introduce the design of MC type FPSO and the model test in waves for the improved mono-column hull, which has more displacement and keeps the motion in waves almost same as the former model.The MC type FPSO has a low frequency response for pitching motion as a semi-submersible has. Such a pitching motion was reduced by the open type anti-pitching tank.The pitching motions in waves of the MC type FPSO and semi-submersible type floating production facility (FPF) were calculated in the typical oil fields in the world and the performances were compared through a year. It was confirmed that the MC type FPSO will be operated even in the North Sea with the same performance as the semi-submersible type FPF.The MC type FPSO will be most suitable for the production testing, early production and production for small oil fields.