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Significant riser oscillations were observed during deep water drilling operations. The riser frequency was above and below the rotation speed of the drill pipe. Laboratory tests and of a riser section has been conducted for these riser drilling-induced vibrations. The first test consists of first measuring the fluid forces between a rotating drill pipe and a riser. In the second test, an elastically supported riser self excites about a rotating drill pipe. An analytical model is developed for predicting these drilling induced riser oscillations. The results show that fluid coupled riser vibrations can result from the fluid forces generated in the annular fluid between the rotating drill pipe and the riser. [ABSTRACT FROM AUTHOR]

The last decade has seen a trend towards the implementation of general purpose non-linear finite element analysis programs for all types of subsea analysis, not only pipelines & risers operating at high temperature and pressure but also spools, termination structures and manifolds. This paper reports innovative processing for Abaqus, written in the Python scripting language, that has been used successfully on subsea structure and pipeline Sc riser system models to enhance output from reeling simulations and in-place analysis, including lateral buckling and free span assessments, to implement structural code checks, to design spools and provide general-purpose output. The benefits to engineers of being able to use the technology effectively, understand its limitations and then critique and improve the methods are discussed. [ABSTRACT FROM AUTHOR]

Using traditional method to disconnect the hang-off risers on offshore floating platform is very time consuming, if there are any new method which can reduce the time to do such work, it will bring very big economic benefit. With this purpose, creative scheme incorporate with power cable seal and riser over bend prevention technology have been introduced by the author. Using this new scheme to conduct riser disconnection work, the actual work time was reduced more than half comparing to traditional recovery method. [ABSTRACT FROM AUTHOR]

Subsea umbilicals exposed to ocean currents are susceptible to Vortex Induced Vibrations (VIV). The possible fatigue damage resulting from this VIV requires careful calculation and prediction of the response. A key characteristic of umbilicals is its large flexibility with respect to bending, in particular due to inter-layer sliding between helically wound layers. This complex mechanical bending performance gives rise to a moment-curvature hysteresis of the cross section, also called stick-slip hysteresis. The stick-slip hysteresis behaviour of an umbilical results in frictional energy dissipation during slipping, which can be characterised by a viscous damping ratio. This stick-slip damping is mode number and mode amplitude dependent and can significantly influence umbilical VIV fatigue life prediction. Methods to incorporate stick-slip damping in prediction methods has been the focus of recent industry research as the predicted fatigue damage rate of deepwater umbilicals without the inclusion of stick-slip damping effects have been prohibitively large. With stick-slip damping included, a greater level of total damping will result and with it a reduction in the predicted amplitude of response and fatigue damage rate. This paper presents the first known implementation of mode number and mode amplitude dependent damping in a VIV prediction scheme. A beta version of a the industry's most widely used VIV prediction tool has been developed to allow for both mode number and mode amplitude dependent structural damping, enabling an accurate application of stick-slip damping. An iterative solver has also been implemented for convergence on the correct VIV solution. To demonstrate the implementation of this new capability, a case study based on a deepwater umbilical is presented. This paper also introduces a simplified screening method, to assist in determining from the outset whether an umbilical will enter into any significant stick-slip regimes that would affect an increase in structural damping. The application of the methodology and tools presented in this paper can be extended to other helically wound flexible structures, such as unbonded flexible risers. [ABSTRACT FROM AUTHOR]

Deepwater drilling riser is the key component of offshore drilling rig and directly affects safety and efficiency of offshore drilling operation. Therefore, Integrity management (IM) of deepwater drilling riser is significant for successful field operation. With the effect of serious environment loads in South China Sea, including frequent typhoon and high speed soliton, IM of deepwater drilling riser confronts with severe challenges. Based on Detection and monitor, IM assessment method is proposed, suitable instrument and software systems are developed in this paper. Monitor system, which is helpful for operator to know the real time status of drilling riser, monitors main parameters of drilling riser including VIV, flex joint angle, stress, current speed and floating rig position. With sonar transfer plan, monitor system is developed and applied in 3 deepwater wells drilled by HYSY981 semisubmersible drilling rig, complete real time data is obtained. Simultaneously, based on ACFM (alternating current field measurement) method, rapid inspection technology of riser is proposed, it can timely and effectively inspect defect of riser such as micro-crack, corrosion, etc. Combine with monitor data and integrity comprehensive assessment theory, design of integrity evaluation software arc introduced, including mutual verification of monitor data, inspecting data and assessment method of fatigue life and fatigue reliability improvement method. Evaluation model are proposed, suite hardware and software systems are developed, which comprise IM series technique of deepwater drilling riser. [ABSTRACT FROM AUTHOR]

The article discusses research which examined the optimization process for robust flexible riser manufacture. Topics discussed include some factors considered in the manufacture of flexible riser products, welding, corrosion, metallurgical and pipe manufacturing robustness as the design target, the requirements for process qualification at key manufacturing stages and the concept of process robustness.

The article discusses research which examined the forced oscillation for Ocean Thermal Energy Conversion (OTEC) rser under current. Topics discussed include high relative velocity by the vortex induced vibration (VIV) current, an overview of the design of the riser and relation of the weight and stiffness of the riser to the mode period.

The article discusses research which analyzed and assessed a surface buoy and umbilical strength in irregular waves to determine the global dynamic responses of the buoy system in sea states. Topics discussed include the numerical modeling of the buoy system including a buoy, an umbilical and a riser and coordinate systems to describe the motions of the systems and define the external loads.

The article discusses research which investigated a field trial of a deepwater drilling system in the South China Sea. Topics discussed include the system consisting of a free-standing drilling riser and a big buoyancy unit, base concept and principle, composition of the free-standing riser system and structure of the buoyancy and control instrument.

The article discusses a research study which investigated the dynamic effects of vibration applied in various directions to the top end of the riser on the tension at the top end by executing free-hanging flexible riser model tests in a tank and analysis. It describes the vibration tests used in the study. The relationship between the dynamic response ration and the vibration aplitude is explained. Findings showed that the measurement accuracy of the OrcaFlex program.

The article discusses a study which proposed a device based on the Bernoulli equation and effects of geometric disturbance on flows around a bluff body for suppressing vortex-induced vibration (VIV). Particular focus is given to the harmony and cone-like type of disturbance. Results of the study showed a reduction in oscillating amplitudes at mild and high waviness at occurrence of synchronization of a cylinder without disturbance.

The article discusses the Work-Over Rise Fatigue Monitoring System (WORFMS), a web based database system that monitors the residual fatigue life of a Completion/Work-Over riser developed by KOGT/SEAFlex. The system is integrated with Statoil's Enterprise Content Management (ECM) system (SAP). The system is used for engineering analyses, onshore operation, and offshore operation. Calculation examples are offered.

The article discusses a study which examined the influence of attack angle on the effectiveness of Vortex-Induced Vibration (VIV) suppression by multiple control rods for deepwater riser. It was observed that the VIV responses of riser model may be significantly reduced by the multiple control rods in terms of the measured strain and fatigue damage. Meanwhile, the attack angle adopted in this work has little influence on the VIV suppression in terms of Cross-Flow (CF) or In-Line (IL) responses.

This article discusses a study which aimed to develop a tool for analyzing VIV (vortex-induced vibration) of a slender marine structure. The study calculated KC (Keulegan-Carpenter) numbers distributed along the riser length. It presented case studies of vortex-induced lift force with three kinds of vortex shedding frequencies. It revealed the response by the riser in several frequencies component.

The article discusses a study that examined the installation methods of ocean and jacket risers. It compared the advantages and disadvantages of the installation methods, which include the monorail guide method, the traditional slinging installation method and the J-shape guide pipe method. The use of the slinging installation method in the modification project of QHD33-1 WHPC platform is discussed.

The article describes an experimental method that is used to calculate the correlation length of a conventional flexible model of a marine riser in transverse flow. A rigid and a flexible cylinders were studied, wherein their relative correlation coefficient and correlation length were compared. Based on the distribution of their probability density function (PDF), the flexible cylinder's vortex shedding profile totally differ with that of the rigid cylinder.

The article discusses a study that investigated the vortex-induced vibration (VIV) for flexible riser and pipe models for various engineering conditions. A series of numerical simulations for validating the efficiency of fluid-structure interaction (FSI) solution approach is presented. A detailed interpretation of the coupling mechanism between the VIV and the vortex shedding is also given.

The article discusses a study that investigated a decoupled approach with enhanced strategies to predict the motion of Deep draft multi-spar (DDMS) platform with steel catenary riser (SCR). According to the article, SCR has become a good alternative compared with the traditional flexible riser due to its cheap price. Free-decay tests are performed to identify the SCR induced damping.

The article discusses the use of 3-D local fine mesh method and beam analysis to verify the structural adequacy of the floating, production, storage and offloading (FPSO) hull appurtenances and adjacent offshore area structures. The FPSO's general description note, including objectives, design principles, design conditions, methodologies, and evaluation techniques, is important to meet the strict standards and common Class rule specifications in in-place and towing condition.

The article describes a theoretical model that can be used in developing a riser system in ultra-deepwater levels of more than 4,000 meters. The theoretical model was a weakly-damped oscillator which was applied to reveal the interaction between hung-off risers and internal fluid. It was concluded that in applying the theory for oscillating flows in pipes, the relationships between friction coefficients and Reynolds numbers were confirmed by experimental data.

This article presents a paper about vertical riser VIV simulation in sheared content. The Reynolds-Averaged Navier-Stokes (RANS) numerical method with a chimera domain composition approach was used in order to resolve the flow field. It offers information on the computational fluid dynamics (CFD) method, including governing equations, over-set grids and riser motion equation with structural damping. It concludes that the CFM method shows good potential for long marine riser VIV analysis and VIV-induced fatigue prediction.