The Experts below are selected from a list of 111 Experts worldwide ranked by ideXlab platform
Roger Chang - One of the best experts on this subject based on the ideXlab platform.
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straight talk about Riser Tension and more
ASME 2009 28th International Conference on Ocean Offshore and Arctic Engineering, 2009Co-Authors: Roger ChangAbstract:One of most confusing issues in Riser engineering is the Riser Tension. The infamous effective Tension equation relates it to the so-called material Tension with external and internal pressures. Controversy remains after numerous papers published trying to clarify the subject, because different interpretations were presented by different authors. Instead of explaining this ‘abstract’ equation mathematically using the free body diagram and differential equation as done in the literatures, this paper presents a down-to-earth interpretation that follows the Riser loading history which starts with the Effective Weight to re-derive the same equation. Four keys to solve the Riser Tension mystery are identified; they are the hydrostatic head pressure vs. applied pressure, pressure generates the pressure end cap load vs. none generated, the vertical (top-Tensioned) Riser vs. bent (catenary) Riser, and the single string Riser vs. multiple strings Riser. Based on these four keys, this paper will address the difference between the effective Tension and material Tension and identify which Tension is to be used in the stress calculation. Also presented in the paper is the driver-reactor theory developed to explain the Tension load distribution among Riser strings due to Poisson’s effect with the applied pressure.Copyright © 2009 by ASME
Svein Saevik - One of the best experts on this subject based on the ideXlab platform.
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vortex induced vibrations of a vertical Riser with time varying Tension
Procedia Engineering, 2017Co-Authors: Mats Jorgen Thorsen, Svein SaevikAbstract:Abstract Numerical simulations of a vertical Tensioned Riser in a sheared flow are performed, where the Riser top end oscillates sinusoidally in the vertical direction. The oscillating top-end motion causes Tension variations and changes in the natural frequencies of the Riser. The flow around the structure causes vortex shedding, oscillating lift forces and vortex-induced vibrations (VIV). It is well-known that the vortex shedding is affected by structure motion, and may lock on to the Riser’s natural frequencies. However, the vortex shedding frequency must remain close to the Strouhal frequency, and may therefore excite different modes of vibration as the Riser Tension changes. With this in mind, the overall aim of this paper is to investigate how Tension variations affect the VIV response. The Riser dynamics are simulated in time domain using a non-linear finite element structural model combined with an empirical hydrodynamic load model. The latter includes a synchronization model which simulates how the vortex shedding reacts to the structure motion to obtain lock-in. Simulations are run using different amplitudes and frequencies for the top-end motion, and the resulting cross-flow displacements and bending strains are studied. The results show that, when the Riser top-end oscillates, the VIV response contains several modes, and the dominating mode may vary with time. The number of active modes are found to be strongly dependent on the period of the Riser Tension.
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Force Variations on Heave Compensating System for Ultra-Deepwater Drilling Risers
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Ronny Sten, Michael Rygaard Hansen, Carl M. Larsen, Svein SaevikAbstract:This paper discusses modeling aspects related to dynamic analysis of deep water drilling Risers. These Risers must have a heave compensator that maintains a near constant Tension in the Riser independent on platform motions. Traditional Riser analysis will apply constant top Tension or a simple parametric model that may give approximate Tension variation. The present paper describes an alternative analysis procedure that consists of the following step: • Global Riser analysis including calculation of dynamic stroke of the heave compensator from platform motions and Riser dynamics. A “pipe-in-pipe” approach is used to represent the hydraulic cylinders. • Calculation of dynamic Tension variation from an analysis of the hydraulic Tensioner system. The dynamic stroke found from the first analysis is applied as known piston motions in this analysis. • Identification of parameters in a simple model for dynamic Tension variation from the results from the second analysis. • Use of the simple model in a second global Riser analysis. The difference between the two Riser analyses can hence be found, which represents the error one must expect from a traditional Riser analysis with constant Riser Tension. A case study with realistic data is reported. The conclusion is that the constant Tension model is valid for small heave motions only, while the parametric Tensioner model can give almost correct results for Tension variation. However, the parametric model must be tuned for each case. Hence, an integrated model that accounts for Riser dynamics and pressure variation in the Tensioner system should preferably be developed.Copyright © 2010 by ASME
Shankar Bhat Aramanadka - One of the best experts on this subject based on the ideXlab platform.
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Tension variations of hydro pneumatic Riser Tensioner and implications for dry tree interface in semisubmersible
Ocean systems engineering, 2017Co-Authors: Hooi Siang Kang, Shankar Bhat AramanadkaAbstract:In real sea environments, excessive dynamic axial Tension variations can be exerted on the top-Tensioned Risers (TTRs) and lead to structural integrity issues. The traditional Riser-Tension-variation analysis, however, by using parametric formulation is only conditionally valid under certain strict limits and potentially underestimates the total magnitudes of Tension variations. This phenomenon is especially important for the long stroke Tensioner in dry-tree semisubmersible with larger global heave motion and longer stroke. In this paper, the hydro-pneumatic Tensioner (HPT) is modeled in detailed component-level which includes a set of hydraulic and pneumatic components. The viscous fluid frictional effect in the HPT is considered. The main objectives are (i) to develop a detailed Tension variation model of the HPT; (ii) to identify the deviations between the conventional parametric formulation and component-level formulation; (iii) to numerically analyze the Tension variation of long stroke Tensioner in a dry-tree semisubmersible (DTS). The results demonstrate the necessity of component-level formulation for long stroke Tensioner in the development of DTS.
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A Large Deck Extendable Draft Platform Design for Ultra-Deepwater in the Gulf of Mexico
24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 1 Parts A and B, 2005Co-Authors: John Murray, Anil Sablok, Todd Demerchant, Lixin Xu, Tim Finnigan, Shankar Bhat AramanadkaAbstract:A new delivery scheme based on an Extendable Draft Platform (EDP), designed for large fields in ultra-deepwater, offers potential benefits that minimize start-up costs and enhance overall economics. This paper describes an EDP design intended for deployment in water depth of 8,500 ft in a Gulf of Mexico environment. This deck design is one of the largest to date, using the EDP delivery method. The paper discusses design philosophy in detail, explaining the unique design features of the topsides for dockside commissioning, the deck connection system, and the Riser systems and their integration. The topsides has process capacity of 200,000 bopd and about 475 mmcfd of gas. The deck also supports a drill rig with a hook capacity of 1,500 kips. The 40,000-ton topsides are 316 ft by 316 ft, supported by four 76-ft diameter columns. In addition to supporting the equipment, the topsides design supports 12,500 tons of Riser Tension. The complete process and drilling systems are assembled and commissioned dockside in less than 40 ft water depth. The entire system is floated on the deck barge, with the columns lowered through the deck and locked into position on site. Then the columns are de-ballasted, and the platform is raised to the operating draft. The top Tensioned Risers (TTRs) are supported by hydraulic Tensioners. The mooring system, a major component of the lowering mechanism that deploys the EDP, comprises 12 lines composed of chain and polyester rope. These lines are pre-set and connected to the hull prior to raising the deck.© 2005 ASME
David Walters - One of the best experts on this subject based on the ideXlab platform.
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Tension and Expansion Analysis of Pipe-In-Pipe Risers: Part B Finite Element Modeling
2013Co-Authors: David WaltersAbstract:We developed a mathematical model for accurately calculating the pipe-in-pipe Riser Tension and elongation in Part A of the paper. In this Part B, we focus on finite element modeling of the multi-string Riser system. The simulations are performed using two widely used Riser analysis finite element software, OrcaFlex and Flexcom. A Tensioner supported pipe-in-pipe TTR system is studied. Special measures and considerations in modeling the pipe-in-pipe features are discussed. The finite element analysis solutions are benchmarked against theoretical results considering weight, temperature, pressure, and Tensioner loads. Good agreements, including Riser stroke and Tension distributions between the inner and outer Risers along the length of the Riser, are observed. The Riser dynamic analysis with environmental loads is subsequently performed with finite element software.
Filip Van Den Abeele - One of the best experts on this subject based on the ideXlab platform.
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Assessment of pipeline walking with coupled triggering mechanisms by finite element approach
Volume 5B: Pipeline and Riser Technology, 2015Co-Authors: Michail Birdas, Narakorn Srinil, Filip Van Den AbeeleAbstract:Asymmetric loading/unloading profiles during the start-up and shut-down operations of high pressure high temperature pipelines may cause an accumulated axial displacement over several operational cycles known as Pipeline Walking phenomenon. This pipeline walking can be triggered by several factors e.g. the seabed slope, Riser Tension and thermal transients. Several studies have been carried out in the literature regarding the influence from individual factors; nevertheless, very little has been made in the evaluation of coupled triggering mechanisms, common for a pipeline segment. This paper investigates the pipeline walking phenomenon using finite element modelling and analysis software SAGE Profile 3D versus standard analytical formulae. The keys aims are (i) to study the interaction and coupling between the walking triggering mechanisms by comparing coupled and uncoupled analyses, and (ii) to compare the obtained numerical results with analytical predictions, commonly used in the subsea industry. Depending on the pipeline and soil properties, the effect of triggering mechanisms is parametrically investigated with varying pipeline Tension and seabed slope for a specific thermal gradient profile. It is found that the common approach to sum up the individual walking rate by the uncoupled analysis for a combination of any two triggering mechanisms, underestimates the walking phenomenon when compared with the coupled analysis. This highlights how attention must be paid to the interaction mechanism. In addition, this study emphasizes that the analytical models severely overestimate the pipeline walking phenomenon, especially when more than one triggering mechanisms are present.
