• Journal of the Society of Naval Architects of Korea
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• v.53 no.4
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• pp.258-265
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• 2016

A flexible riser consists of several layers which have different materials, shapes and functions. The layers designed properly can take the design load safely, and each property of layer provides a complexity of flexible riser. Such complexity/unit-property is an input for global analysis of flexible riser. There are several approaches to calculate the complexity of flexible riser, those are experimental, numerical and theoretical methods. This paper provides a complexity from numerical and theoretical analysis for 2.5 inch flexible riser of which details and the experimental data are already produced under tension, external pressure, and bending moment. In addition, comparison of stiffness and stress are also provided. Especially, analysis of stress could lead to researches on ultimate strength or fatigue strength of flexible risers.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.650-658
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• 2021

Flexible risers are usually used as conveying systems to bring ocean resources from sea bed up to onshore. Under ocean environments, risers need to bear complex loads and it is crucial to comprehensively examine riser's configurations and to analyze structural dynamic performances under excitation of bottom vehicle motions, to guarantee structural safe operation and required service lives. In this study, considering a saddle-shaped riser, the influences of some important design parameters, including installation position of buoyancy modules, buoyancy ratio and motion of mining vehicle, on riser's configuration and response are carefully examined. Through our FEM simulations, the spatial distributions of structural tensions and curvatures along of riser length, under different configurations, are compared. Then, the impacts of mining vehicle motion on riser dynamic response are discussed, and structural tolerance performance is assessed. The results show that modules installation position and buoyancy ratio have significant impacts on riser configurations. And, an appropriate riser configuration is obtained through comprehensive analysis on the modules positions and buoyancy ratios. Under this proposed configuration, the structural tension and curvature could moderately change with buoyancy modules and bottom-end conditions, in other words, the proposed saddle-shaped riser has a good tolerance performance to various load excitations.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.2
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• pp.112-118
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• 2010

The numerical study about the vortex-induced vibration and vortex shedding in the wake has been presented. Prior to the numerical simulation of flexible riser systems concerning engineering conditions, efficiency validating of the proposed FSI solution method have been performed. The comparison between numerical simulation and published experimental data shows that the CFD method designed for FSI solution could give acceptable result for the VIV prediction of flexible riser/pipe system. As meaningful study on VIV and vortex shedding mode with the focus on flexible riser model systems, two kinds of typical simulation cases have been carried out. One was related to the simulation of vortex visualization in the wake for a riser model subject to forced oscillation, and another was related to the simulation of fluid-structure interaction between the pipes of coupled multi-assembled riser system. The result from forced oscillation simulation shows that the vortex-induced vibration with high response frequency but small instantaneous vibration amplitude contributes to vortex conformation as much as the forced oscillation with large normalized amplitude does, when the frequency of forced oscillation was relatively high. In the multi-assembled riser systems, it has been found that the external current velocity and the distance between two pipes are the critical factors to determine the vibration state and the steady vibration state emerging in quad-pipe system may be destroyed more easily than dual-pipe system.

• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.15-22
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• 2004

Static and dynamic analyses of a very flexible and light riser, for upwelling the deep ocean water, is performed. In this numerical study, an implicit finite difference algorithm is employed for three-dimensional riser equations. Fluid non-linearity and bending stiffness are considered and solved, using the Newton-Raphson iteration. Maintaining the depth of end point of a flexible and light riser is very important for upwelling deep ocean water in a floating type development system. Weight is attached at the end point of the riser in order to maintain its intake depth. It is designed under the strong surface current and the configuration of the rise is predicted. In the dynamic analysis, the tension variation at the top point of the riser is presented. T e results of this study can contribute to the design of the development system in floating type for upwelling deep ocean water.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.2
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• pp.195-201
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• 2014

Flexible risers have been used extensively in recent years for floating and early production systems. Such risers offer the advantage of having inherent heave compliance in their catenary thereby greatly reducing the complexity of the riser-to-rig and riser-to subsea interfaces. Another advantage with flexible risers is their greater reliability. Concerns about fatigue life, gas permeation and pigging of lines have been overcome by extensive experience with these risers in production applications. In this paper, flexible riser analysis results were compared through coupled and uncoupled dynamic analyses methods. A time domain coupled analysis capability has been developed to model the dynamic responses of an integrated floating system incorporating the interactions between vessel, moorings and risers in a marine environment. For this study, SPM (Single Point Mooring) system for an FSU in shallow water was considered. This optimization model was integrated with a time-domain global motion analysis to assess both stability and design constraints of the flexible riser system.

• Journal of Coastal Disaster Prevention
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• v.1 no.4
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• pp.149-155
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• 2014

Flexible risers have been used extensively in recent years for floating and early production systems. Such risers offer the advantage of having inherent heave compliance in their catenary thereby greatly reducing the complexity of the riser-to-rig and riser-to subsea interfaces. Another advantage with flexible risers is their greater reliability. Concerns about fatigue life, gas permeation and pigging of lines have been overcome by extensive experience with these risers in production applications. In this paper, flexible riser analysis results were compared through coupled and uncoupled dynamic analyses methods. A time domain coupled analysis capability has been developed to model the dynamic responses of an integrated floating system incorporating the interactions between vessel, moorings and risers in a marine environment. For this study, SPM (Single Point Mooring) system for an FSU in shallow water was considered. This optimization model was integrated with a time-domain global motion analysis to assess both stability and design constraints of the flexible riser system.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.323-328
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• 2003

A basic design on a flexible riser in a floating type development system for upwelling deep ocean water is presented. In the numerical study, an implicit finite difference algorithm is employed for three-dimensional riser equations. Fluid and geometric non-linearity and bending stiffness are considered and solved by Newton-Raphson iteration. To keep the depth of end point of a flexible and light riser is very important for upwelling deep ocean water in a floating type development system. Weight attached at the end point of the riser in order to keep its intake depth is designed under the strong surface current and the configuration of the riser is predicted. The results of this study can be contributed to the design of the development system in floating type for upwelling deep ocean water.

• Ocean Systems Engineering
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• v.6 no.2
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• pp.129-141
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• 2016

Due to the structural complexity, the response of a flexible riser under axisymmetric loads is quite difficult to determine. Based on equilibrium conditions, geometrical relations and constitutive equations, an analytical model that can accurately predict the axisymmetric behavior of flexible risers is deduced in this paper. Since the mutual exclusion between the contact pressure and interlayer gap is considered in this model, the influence of the load direction on the structural behavior can be analyzed. Meanwhile, a detailed finite element analysis for unbonded flexible risers is conducted. Based on the analytical and numerical models, the structural response of a typical flexible riser under tension, torsion, internal and outer pressure has been studied in detail. The results are compared with experimental data obtained from the literature, and good agreement is found. Studies have shown that the proposed analytical and numerical models can provide an insightful reference for analysis and design of flexible risers.

• Ocean Systems Engineering
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• v.5 no.2
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• pp.77-89
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• 2015

As the exploitation of oil and gas resources advances into deeper waters and harsher environments, the design and analysis of the flexible risers has become the research focus in the offshore engineering filed. Due to the complexity of the components and the sliding between the adjacent layers, the bending response of the flexible risers is highly non-linear. This paper presents the finite element analysis of the flexible risers under bending loads. The detailed finite element model of the flexible riser is established in ABAQUS software. This finite element model incorporates all the fine details of the riser to accurately predict its nonlinear structural behavior. Based on the finite element model, the bending moment-curvature relationships of a flexible riser under various axisymmetric loads have been investigated. The results have been compared with the analytical ones obtained from the literature and good agreements have been found. Moreover, the stress of the tendon armors has been studied. The non-linear relationship between the armor tendons' stress and the bending loads has been obtained.

• Journal of Ocean Engineering and Technology
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• v.31 no.5
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• pp.364-370
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• 2017

A numerical model based on the mode superposition method is used to study the vortex-induced vibration response characteristics of a deep-sea riser such as steel catenary riser (SCR). A steel catenary riser can be modeled using a flexible cable with simple supports at both ends. The natural frequency, mode shape and mode curvature of the riser are calculated and the vortex-induced vibration response of the riser is obtained using the equilibrium of the input and output power. The mode superposition method is applied to the vibrational stresses for each mode to calculate the overall riser fatigue life.