Tensioners

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 1340076 Experts worldwide ranked by ideXlab platform

Atila Ertas - One of the best experts on this subject based on the ideXlab platform.

Donogh Lang - One of the best experts on this subject based on the ideXlab platform.

  • modelling of marine riser tensioner load variations and implications for minimum top tension settings in drilling risers
    ASME 2012 31st International Conference on Ocean Offshore and Arctic Engineering, 2012
    Co-Authors: Conor Gallagher, Dara Williams, Donogh Lang
    Abstract:

    As the pace of deepwater oil and gas exploration continues to grow, so too does demand for modern drilling vessels with equipment capable of operating in water depths of 10,000ft or greater. These greater water depths place significant demands on the drilling riser and the riser tensioning system. Modern riser Tensioners are complex hydro-pneumatic systems and far from applying a constant top tension, the stiffness and damping characteristics associated with the tensioner mean that the applied tension can vary substantially as the tensioner strokes in response to vessel heave. As a result it is critical that the riser tensioner system response be captured in sufficient detail when evaluating the loads on the drilling riser.Riser tensioner systems for deepwater drilling must be capable of supplying the required tension to satisfy the minimum stability tension requirement, as per API RP 16Q; however this recommended practice does not adequately account for dynamic tensioner load variation, which can be up to 50% of the nominal tension. For deepwater drilling riser systems, where riser load limits are being approached, accurate modeling of the tensioner system load variation is required to ensure that the riser does not experience compression or excessive stresses. Furthermore, as the dynamic tension variations are largely velocity dependent, they can be relatively independent of water depth. Thus larger percentage variations in tension are experienced at low tensions when compared to higher tensions. This is an important consideration when calculating minimum top tensions for deepwater drilling rigs in shallower water depths.This paper presents a comparison of the response of a direct-acting riser tensioner (DAT) system for a range of environments. The comparison is based on results from detailed tensioner models that include the individual hydraulic and pneumatic components of the tensioner system and that are fully integrated with a non-linear 3D structural FE analysis tool [1]. The FE model is based on a widely-validated-non-linear software tool [3]. The detailed tensioner model has been validated against manufacturer performance data for existing in-service tensioner systems. The detailed tensioner model has also been used as part of a drilling riser recoil analysis study [1] which provided a good comparison of recoil analysis results against a published recoil test case. The impact on the global riser response of accurately modeling the tensioner system behavior is demonstrated, while the implications for the calculation of minimum top tension are also discussed.Copyright © 2012 by ASME

T. J. Kozik - One of the best experts on this subject based on the ideXlab platform.

Oriol Rijken - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Validation of a Numerical Model for a Dry-Tree Semisubmersible in Benign Environments
    Volume 1B: Offshore Technology, 2014
    Co-Authors: Bruce Martin, Oriol Rijken, Kent Davies
    Abstract:

    The offshore industry has spent the last several years developing semisubmersible platforms capable of supporting both drilling and production activities. The production trees are located on top of the top tensioned risers (TTRs) on a Dry Tree Semisubmersible. A key challenge in the design of these vessels is to reduce the heave motion as much as possible to enable the use of state-of-the-art riser Tensioners. A model test campaign was executed as part of the developmental program. The primary objective of this campaign was to improve the accuracy of the numerical tools to be used in the design process.Riser Tensioners are typically hydro-pneumatic devices, with a nonlinear tension-stroke relationship. A riser tensioner was developed at model scale which had a similar nonlinear behavior to the prototype. Examining the effect of this tensioner on the global motions was an additional objective of this test campaign. The techniques used to model this nonlinear spring is described, and its effect on global motions investigated.A key challenge in model testing platforms intended for ultra-deep water (e.g. greater than 7000 ft) is the modeling of the mooring and riser system. The premise for the design of the model mooring system is 1.) maintain as best as possible the force-offset relationship of the mooring lines and 2.) be able to describe the model test configuration in the numerical tools to be used for global design. The near taut behavior of the prototype mooring system is modeled using heavy chain and a high-catenary mooring line.© 2014 ASME

  • motion reduction for spar platform with hydro pneumatic Tensioners
    ASME 2011 30th International Conference on Ocean Offshore and Arctic Engineering, 2011
    Co-Authors: Xiaoqiang Sean Bian, Michael W Spillane, Oriol Rijken
    Abstract:

    The Spar platform is one of the options to support dry-trees from a floating unit, particularly in increasing water depth. The recent Spar developments in Gulf of Mexico (GOM) favor Spar Supported Hydro-pneumatic Tensioners to support Top Tensioned Vertical Risers (TTR). The trend has been made possible by, as well as promoted the long-stroke RAM type hydro-pneumatic tensioner market. Currently up to 35 ft stroke Tensioners are technically available and 28 ft ones are installed and field tested on GOM spars. The primary advantage, compared with buoyancy cans, is its possible integrated installation. Aside from taking payload from the hull, hydro-pneumatic Tensioners have stiffness and can effectively reduce the heave period closer to the dominant wave period. It’s imperative to control the resonance motion, particularly of a classic spar which is generally low damped in heave. This study investigates the heave reduction by using an air-spring-water-column Vibration Absorber (VAB) mounted vertically inside the spar, the vibration absorbers consist of vertical caissons, open at the bottom to the sea and closed at the top. Each caisson consists of a water column providing mass (unsupported by the Spar) and a dual-chamber air spring, which interacts with the Spar. The motion of the water column produces pressure variations out-of-phase with the resonant motions of the Spar, resulting in reduced heave. Damping of the vibration absorber is provided by an orifice connecting the two air chambers, and is used to allow effective operation across varying frequencies. The detailed background of VAB and the application can be found in references [1] and [4]. This paper describes a classic spar platform with its heave motion reduced by using VAB to the point that market available hydro-pneumatic Tensioners can be used. The theory of the Vibration Absorber and the procedure of configurating the system are introduced in this paper. The platform, mooring system and global motion analysis of the proposed facility are described for GOM applications with performance comparable to an existing truss Spar platform. Both frequency domain and time domain analysis of the coupled motions are included in this study.Copyright © 2011 by ASME

Guttorm Grytoyr - One of the best experts on this subject based on the ideXlab platform.

  • Marine drilling riser disconnect and recoil analysis
    2011
    Co-Authors: Guttorm Grytoyr, Partha Sharma
    Abstract:

    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.

  • Improving Operating Window for Disconnect Operations of CWO Risers
    29th International Conference on Ocean Offshore and Arctic Engineering: Volume 5 Parts A and B, 2010
    Co-Authors: Guttorm Grytoyr
    Abstract:

    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

  • Methodology for Disconnect Analysis of CWO Risers in Random Seas
    Volume 3: Pipeline and Riser Technology, 2009
    Co-Authors: Guttorm Grytoyr, Anne Marthine Rustad, Nils Sødahl, Per Christian Bunaes
    Abstract:

    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. Recoil of Marine Drilling Risers has been the subject of several research papers over the past two decades. Some examples are listed in references [2] through [7]. 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 current industry practice is to use a regular wave approach in the analysis. The wave frequency is varied in order to find the maximum response, and hence one is actually searching for the extreme response, without paying attention to the probability that this will occur. In this paper a new method is presented, where the analysis is based on an irregular wave approach and the Monte Carlo technique, using time-domain simulations. Acceptance criteria are established based on a stochastic analysis, and are based on target levels of probability of exceedance. 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 both regular and irregular waves. Comparison of the resulting allowable wave height indicates that using the approach presented here with irregular waves will give a considerable increase in the operating window, and the resulting operability, compared to a regular wave analysis.Copyright © 2009 by ASME

Related terms

Tensioners - 15 days free trial to Access Experts & Abstracts