The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Svein Sævik - One of the best experts on this subject based on the ideXlab platform.
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Static Analysis of interaction between two adjacent top tensioned Risers with consideration of wake effects
Ocean Engineering, 2019Co-Authors: Deqiang Tian, Bernt J. Leira, Honghai Fan, Svein SævikAbstract:Abstract Collision between adjacent Risers has become an important issue as the oil and gas industry moves to deeper waters. In order to estimate the clearance between two marine Risers, a static Analysis which is mainly concerned with the wake effects is performed in this paper. A new wake model, which is used to predict the wake flow around the downstream Riser, is developed based on Prandtl's shearing stress hypothesis. The wake effects with respect to Riser interference in uniform current flow are then investigated. In this work, the two Risers are both simplified as circular cylinders top-tensioned and pinned at the bottom. A procedure for iteratively predicting the wake velocity distribution and estimating the clearance between two Risers is introduced to find the final convergent result by combining the new wake model with the global Riser Analysis software Riflex. The effects of different factors like Riser spacing, top tension force and current velocity are also studied. The results indicate that these factors significantly influence the Riser interference. Since the current velocity cannot in general be controlled for a specific site, the Riser spacing and the top tension force become the primary design parameters that can be chosen by the operator.
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Theoretical and experimental studies of stresses in flexible pipes
Computers & Structures, 2011Co-Authors: Svein SævikAbstract:This paper presents one model for predicting stresses from axi-symmetric effects and two alternative formulations for predicting bending stresses in tensile armour layers of non-bonded flexible pipes. The models were developed to comply with the framework of non-linear finite element technology allowing direct implementation into existing codes for flexible Riser Analysis, all based on corotated kinematics allowing for large displacements and small strains. Experimental studies were further carried out using strain measurements from fibre-optic Braggs to validate the performance of both formulations in terms of bending stresses and fatigue.
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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, Carl M. Larsen, Michael Rygaard Hansen, Svein SævikAbstract: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
Adrian Connaire - One of the best experts on this subject based on the ideXlab platform.
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a global local fretting Analysis methodology and design study for the pressure armour layer of dynamic flexible marine Risers
Tribology International, 2020Co-Authors: Sinead M Ohalloran, Adrian Connaire, Annette M. Harte, Sean B. LeenAbstract:Abstract In this paper, a global-local fretting design methodology for the pressure armour layer of flexible marine Risers is outlined. This includes global dynamic Riser Analysis, geometrical and analytical sub-models and local nub-groove contact finite element Analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical Riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic Riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.
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Advancements in subsea Riser Analysis using quasi-rotations and the Newton–Raphson method
International Journal of Non-linear Mechanics, 2015Co-Authors: Adrian Connaire, Patrick O’brien, Annette M. Harte, Aonghus O’connorAbstract:Abstract Beam structures undergoing finite deflections and rotations in space have extensive application in the subsea industry particularly for the Analysis of holistic systems with larger numbers of mooring and Riser components. In using the finite element Analysis approach, there is an increasing requirement for large element sizes which preserve accuracy with regard to the coupling of axial, bending and torsion response. The authors outline a method for improving the current state of practice for the Analysis of Riser systems. The approach draws on the convected coordinates method, Euler–Bernoulli beam theory, the principle of virtual work and the finite element method. Two quasi-rotation measures are developed including a quasi-material rotation definition for rotational deformation relative to the convected axis of a beam and a quasi-space rotation definition to deal with the path dependent nature of rotations in three dimensions. The novel aspect of this work is to relate the rate of change of the quasi-material rotation vector along the beam axis to a linear transformation of the beam axis rate-of-rotation vector through utilising the convected coordinates axes system. In this way, incremental values of quasi-material rotation are directly linked to incremental values of nodal quasi-space rotation and a global Newton–Raphson solution technique for interconnecting beam elements is straightforward to assemble. Furthermore, this leads to accurate definitions of coupled axial, bending and torque response for beams with significant deflection. The approach has particular advantages in the Analysis of subsea Riser sections. Also, the accuracy of the solution is preserved for a fewer number of elements compared to alternative solutions for computationally sensitive load cases with highly non-linear loading regimes.
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advancements in subsea Riser Analysis using quasi rotations and the newton raphson method
International Journal of Non-linear Mechanics, 2015Co-Authors: Adrian Connaire, Annette M. Harte, Patrick Obrien, Aonghus OconnorAbstract:Abstract Beam structures undergoing finite deflections and rotations in space have extensive application in the subsea industry particularly for the Analysis of holistic systems with larger numbers of mooring and Riser components. In using the finite element Analysis approach, there is an increasing requirement for large element sizes which preserve accuracy with regard to the coupling of axial, bending and torsion response. The authors outline a method for improving the current state of practice for the Analysis of Riser systems. The approach draws on the convected coordinates method, Euler–Bernoulli beam theory, the principle of virtual work and the finite element method. Two quasi-rotation measures are developed including a quasi-material rotation definition for rotational deformation relative to the convected axis of a beam and a quasi-space rotation definition to deal with the path dependent nature of rotations in three dimensions. The novel aspect of this work is to relate the rate of change of the quasi-material rotation vector along the beam axis to a linear transformation of the beam axis rate-of-rotation vector through utilising the convected coordinates axes system. In this way, incremental values of quasi-material rotation are directly linked to incremental values of nodal quasi-space rotation and a global Newton–Raphson solution technique for interconnecting beam elements is straightforward to assemble. Furthermore, this leads to accurate definitions of coupled axial, bending and torque response for beams with significant deflection. The approach has particular advantages in the Analysis of subsea Riser sections. Also, the accuracy of the solution is preserved for a fewer number of elements compared to alternative solutions for computationally sensitive load cases with highly non-linear loading regimes.
Kazuo Miura - One of the best experts on this subject based on the ideXlab platform.
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drilling Riser Analysis during installation of a wellhead equipment
ASME 2013 32nd International Conference on Ocean Offshore and Arctic Engineering, 2013Co-Authors: Lucas Cantinelli Sevillano, Jose Ricardo Pelaquim Mendes, Celso Kazuyuki Morooka, Kazuo MiuraAbstract:In offshore petroleum drilling, the BOP stack is run into the sea by a string, composed of long and wide-bore pipes, called the marine drilling Riser. It also connects the BOP stack (BOP + LMRP) on the wellhead to the drilling vessel at the sea surface, serving as conduit between them.While being lowered down, a special Riser spider is used to support the Riser. During this operation, the hanging Riser is under the effects of sea current, waves and displacements induced by sea surface drilling vessel motions.The discovery of petroleum fields in deeper waters, usually in remote and harsh environments, makes it a requirement for the Riser to withstand more severe conditions. Nevertheless, Riser design and failure Analysis during this operation is a seldom studied topic, even though drilling in ever increasing water depths imply the Riser is subject to risks inherent to running a BOP for a longer period of time. It is of utmost importance the adequate modeling of the system’s response during this operation, in order to safely evaluate failure cases due to extreme static and dynamic stresses.As such, the present paper describes and proposes a methodology developed for the Analysis of extreme stresses that act over the Riser during the BOP running. Case studies were conducted for a water depth up to 2000 m. Numerical simulations were run to evaluate system’s static and dynamic behavior due to environmental loading.As a result conclusions were drawn regarding operation limits in ultra-deep waters. Results are shown through charts that delimit ocean conditions and vessel’s response that are secure to operate under.Copyright © 2013 by ASME
Guttorm Grytoyr - One of the best experts on this subject based on the ideXlab platform.
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experimental and numerical study of a top tensioned Riser subjected to vessel motion
Ocean Engineering, 2019Co-Authors: Elizabeth Passano, Kristoffer H. Aronsen, Michael Tognarelli, Guttorm Grytoyr, Elizbar Buba KebadzeAbstract:Abstract Model tests of a top tensioned Riser (TTR) model were carried out as a part of a joint industry project, with the purpose of better understanding the dynamic behaviour of drilling Riser and verifying the calculations of the Riser Analysis tools. Sinusoidal motion in one direction was imposed at the top end of the Riser model to simulate vessel motion. The tests were carried out in still water, accelerations and bending strains were measured along the Riser model. Numerical simulations were performed using RIFLEX and the predicted global responses were compared with the model tests. This paper discusses interesting aspects of this comparison as well as the general dynamic behaviour of the top tensioned Riser. It was found that the dynamic responses of a TTR with vessel motion can consist of not only the in-line (IL) responses due to vessel motion at the Riser top end, but also cross-flow (CF) vortex-induced vibrations (VIV) under conditions when Keulegan-Carpenter ( K C ) number is relatively small. CF VIV response is estimated using a time domain VIV prediction model and compared to the measured response. The main conclusion is that the IL global dynamic responses and CF VIV responses are predicted sufficiently well.
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Comparison of Global Riser Analysis to Full Scale Measurements on the NCS
Volume 3B: Structures Safety and Reliability, 2017Co-Authors: Guttorm Grytoyr, Max Russo, Kathrine Gregersen, Torfinn Hørte, Kristoffer H. AronsenAbstract:Fatigue of subsea wellhead systems due to wave-induced loads from Riser and rig motions has been subjected to increased attention in recent years. It is expected that calculated Riser loads are conservative, as both input parameters and methodology are associated with some uncertainty. However, it is difficult to quantify the degree of conservatism in analytical results unless reference to measurements can be made.Statoil has conducted drilling Riser load instrumentation campaigns in several locations around the world over the last few years in order to gather high quality data for accurate assessment of the fatigue loads imposed on the subsea wellheads (see e.g. ref. /1/, /2/, /3/, and /17/). Four (4) of these measurements campaigns have been studied in more detail, with the intention to quantify the degree of conservatism to be expected from drilling Riser Analysis. Three (3) of these cases have direct bending moment measurements from strain sensors at the BOP connector elevation, giving high confidence in the results. For one (1) of the cases, the bending moments at the WH have been established by use of indirect methods (ref. /2/). The campaigns have been anonymized; They are from the Norwegian Continental Shelf (NCS), with water depths ranging from 110 to 400m. This paper presents the findings from our comparison of measurements and analytically derived drilling Riser loads from these 4 campaigns. The Analysis models have not been “tuned” to match the measurements. The goal is rather to get a measure of how well Riser analyses are able to predict the real world.The conclusion in this paper is that the global drilling Riser analyses accurately predict the cyclic loads on the subsea wellheads, provided that the input data are known with high degree of detail, including e.g. Riser tension setting; drill pipe tension variation over time; and hydrodynamic loads. We found that scatter in the results is due to the uncertainty inherent to several of the input parameters.It is also shown that the accumulated fatigue damage from a full drilling campaign, can be established with sufficient degree of accuracy with somewhat lower requirement to the level of detail of the input, like e.g. using unidirectional waves instead of short crested waves. Directionality and spreading of the wave field can be handled by use of factors on the damage rate. A directionality factor is proposed, to enable comparison of directionality of the measured response to the predictions from global Analysis.Copyright © 2017 by ASME
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Marine drilling Riser disconnect and recoil Analysis
2011Co-Authors: Guttorm Grytoyr, Partha SharmaAbstract:A methodology is presented for the dynamic Analysis of marine drilling Riser disconnect and recoil using general purpose Riser FEA programs. The methodology includes the effects of mud column discharge, which is a governing effect in the first part of the transient phase, and the effects of pressure loss in the hydraulic lines for the Riser tensioners. The global behavior of the Riser due to, e.g. elasticity and inertia, is automatically accounted for by the Riser Analysis software. The presented methodology is easy to use and can be applied to any Riser system, both conventional wireline and direct acting tensioners. A typical case is selected and analyzed, with emphasis on lift height of the lower Riser package and impulsive loading due to bottoming-out of the tensioners or the telescopic joint. The effect of tension setting is studied, covering a range of settings in order to select the optimum. The methodology enables the Riser system designers to reuse Riser models from the design Analysis. No additional Riser model has to be built for the disconnect and recoil Analysis. All major physical effects are taken into account by the methodology, including detailed cross sectional properties of the Riser system, and the hydraulic and pneumatic response of the tensioner system.
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Improving Operating Window for Disconnect Operations of CWO Risers
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010Co-Authors: Guttorm GrytoyrAbstract:The term ‘Riser recoil’ refers to the situation when the lower end of a top tensioned Riser is released, and the Riser is lifted up by the Riser tensioner and/or top motion compensator system on the supporting vessel. The elastic energy stored in the Riser is then released, and the Riser ‘recoils’. This paper focuses on the case of planned disconnect, and builds on ref. [1] which was based on a simplified Riser Analysis using a rigid body to represent the Riser. In the present paper, the methodology has been applied to an elastic Riser model in the Riser Analysis software RIFLEX, from MARINTEK in Trondheim, Norway, which includes axial damping elements required for modeling of the tensioner systems. Completion and Work Over (CWO) Risers are unique in the sense that they may be simultaneously connected to both the Riser tensioner system and the top motion compensator system of a drilling vessel. A Marine Drilling Riser, on the other hand, is only connected to the Riser tensioner system. Typically the Riser tensioner system has a stroke of ± 8–9 m, whereas the top motion compensator system has only ± 3.5–4 m. It is imperative that the connector is lifted clear of the subsea structure in order to avoid damage to the equipment after the Riser has been disconnected. The operating window for planned disconnect of CWO Risers is severely limited by the available stroke of the top motion compensator. One of the purposes of the disconnect Analysis is to establish the maximum wave height at which there is still sufficient clearance between the connector and the subsea structure after disconnect. Previous experience has shown that this may be the governing limitation for workover operations. The Analysis may also establish a maximum tension level, and seastate, to avoid hard stroke-out of the top motion compensator cylinders. This requires an elastic Riser model, since a rigid body will yield unphysically large impulse loads in case of stroke-out. The current industry practice is to use a regular wave approach in the Analysis. In accordance with ref. [1], the present Analysis is performed with irregular wave analyses. The results are documented through a case study of a typical CWO Riser system connected to a semi-submersible in typical North Sea environmental conditions. The semi-submersible and the CWO Riser system are exposed to irregular waves. Comparison of the resulting allowable wave height shows that using the approach presented here with an elastic Riser model yields less conservative results than the previous methodology with a rigid body model. This should be coupled to the findings with the rigid Riser model, ref. [1], that irregular waves yield a considerable increase in the operating window, and the resulting operability, compared to a regular wave Analysis. Hence, using a regular wave approach combined with a simplified Riser model that neglects the flexibility of the Riser is expected to yield overly conservative results for the EQDP elevation after disconnect.Copyright © 2010 by ASME
Aonghus Oconnor - One of the best experts on this subject based on the ideXlab platform.
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advancements in subsea Riser Analysis using quasi rotations and the newton raphson method
International Journal of Non-linear Mechanics, 2015Co-Authors: Adrian Connaire, Annette M. Harte, Patrick Obrien, Aonghus OconnorAbstract:Abstract Beam structures undergoing finite deflections and rotations in space have extensive application in the subsea industry particularly for the Analysis of holistic systems with larger numbers of mooring and Riser components. In using the finite element Analysis approach, there is an increasing requirement for large element sizes which preserve accuracy with regard to the coupling of axial, bending and torsion response. The authors outline a method for improving the current state of practice for the Analysis of Riser systems. The approach draws on the convected coordinates method, Euler–Bernoulli beam theory, the principle of virtual work and the finite element method. Two quasi-rotation measures are developed including a quasi-material rotation definition for rotational deformation relative to the convected axis of a beam and a quasi-space rotation definition to deal with the path dependent nature of rotations in three dimensions. The novel aspect of this work is to relate the rate of change of the quasi-material rotation vector along the beam axis to a linear transformation of the beam axis rate-of-rotation vector through utilising the convected coordinates axes system. In this way, incremental values of quasi-material rotation are directly linked to incremental values of nodal quasi-space rotation and a global Newton–Raphson solution technique for interconnecting beam elements is straightforward to assemble. Furthermore, this leads to accurate definitions of coupled axial, bending and torque response for beams with significant deflection. The approach has particular advantages in the Analysis of subsea Riser sections. Also, the accuracy of the solution is preserved for a fewer number of elements compared to alternative solutions for computationally sensitive load cases with highly non-linear loading regimes.
