Design Challenges of Top Tensioned Risers in Ultra Deepwater Applications

2011 ◽  
Author(s):  
Yongming Cheng ◽  
Lixin Xu ◽  
Paul Stanton
Keyword(s):  
Production Systems ◽  
Direct Access ◽  
Floating Platform ◽  
Stick Slip ◽  
Capacity Limit ◽  
Global Performance ◽  
Riser Design ◽  
Vessel Motion ◽  
High Payload ◽  
Design Challenges

A Top Tensioned Riser (TTR) system provides direct access to subsea wells from a floating platform for drilling, workover, and completion operations. TTRs have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. This paper investigates design challenges of TTRs in ultra deepwater applications. As application moves to ultra deepwater, challenges of TTRs increase in terms of riser design, analysis, installation and global performance. This paper first introduces a typical TTR configuration in ultra deepwater applications. The TTR design issues cover riser wall thickness which is especially driven by extreme high pressure and high temperature, tension limits, high payload, and long tensioner stroke. The installation concerns come from hook capacity limit, riser Vortex-Induced Vibration (VIV) when the riser is disconnected, and riser bottom drift caused by vessel motion during installation. This paper further investigates the coupling between the risers and floating platform, the interference between riser pairs, riser VIV, and tensioner stick-slip phenomenon. Examples are given to illustrate various aspects of TTRs in ultra deepwater applications. In addition, this paper also explores likely solutions to TTR design challenges.

Time Domain VIV Prediction for Top Tensioned Risers

2010 ◽  
Author(s):  
Yongming Cheng ◽  
Kostas F. Lambrakos ◽  
Roger Burke ◽  
Paul Stanton
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Production Systems ◽  
Vertical Direction ◽  
Direct Access ◽  
Frequency Domain Method ◽  
Floating Platform ◽  
Prediction Program ◽  
Use Of Time ◽  
The Time Domain

Top Tensioned Risers (TTRs) have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. A TTR system provides direct access to subsea wells from a floating platform for drilling, workover, and completion operations. It is often subjected to Vortex-Induced Vibration (VIV) caused by ambient ocean currents or vessel motions. This paper investigates time domain VIV prediction for TTRs used in a typical Spar floating production system. A typical TTR has strong nonlinear and time-varying dynamic characteristics. The existing gaps between the riser and keel guide and between riser top centralizers and the supporting conductor result in intermittent VIV behaviors of the riser. In addition, hydraulic tensioners are widely used to provide tension to a TTR. The tension from tensioners varies with the riser’s dynamic response especially in the vertical direction. The time domain approach, which has been benchmarked and published in about ten technical papers, is thus more appropriate to predict TTRs’ VIV performance than a frequency domain method. This paper first introduces a typical TTR structure and then presents the analysis methodology and features of the time domain VIV prediction program ABAVIV. An example TTR is used to illustrate intermittent VIV behaviors such as top tension, interaction load at the keel guide, and VIV response at the location of top centralizers. This paper further studies the sensitivity of the VIV response to different current profiles. It finally uses the time domain approach to analyze the VIV response of the riser with its boundary conditions fixed and compares the results with those from a frequency domain program. A conclusion is finally drawn about the use of time domain VIV prediction for Spar TTRs.

Investigation of VIV Fatigue Prediction for a Top Tensioned Riser

2009 ◽  
Author(s):  
Yongming Cheng ◽  
Lixin Xu ◽  
Kostas F. Lambrakos ◽  
Karl Muriby
Keyword(s):  
Production Systems ◽  
Direct Access ◽  
Mode Shapes ◽  
Floating Platform ◽  
Finite Element Program ◽  
Prediction Program ◽  
Mode Cutoff ◽  
Element Program ◽  
Offshore Industry ◽  
The Time Domain

Top tensioned risers (TTRs) have been widely used with floating production systems such as Spars and TLPs in deepwater field developments. A TTR system provides direct access to subsea wellheads from a floating platform for drilling, workover, and completion operations. It is often subjected to Vortex-Induced Vibrations (VIVs) caused by ambient ocean currents. This paper investigates the VIV fatigue prediction for a TTR used with a Spar in deep water. The riser VIV predictions are mainly based on the frequency domain program SHEAR7 that is widely used in the offshore industry. The nonlinear finite element program ABAQUS is used to model the riser for the generation of modal data, including natural frequencies, mode shapes and mode curvatures. The riser is modeled using generic beam elements with equivalent section properties. The model considers the lateral supports from the keel guide and hard tank. The riser tensioner is modeled with non-linear springs. The riser VIV is predicted using different SHEAR7 versions. This paper investigates the sensitivity of the results to key parameters such as the type of lift coefficients, mode bandwidth, mode cutoff, and the Strouhal number. In addition, the time domain VIV prediction program ABAVIV is used to compute the VIV response for a few governing current profiles. The results by SHEAR7 are compared with those by ABAVIV.

Truss Spar Vortex Induced Motions: Benchmarking of CFD and Model Tests

2006 ◽  
Author(s):  
John Halkyard ◽  
Sampath Atluri ◽  
Senu Sirnivas
Keyword(s):  
Fluid Dynamics ◽  
Best Practices ◽  
Turbulence Modeling ◽  
Production Systems ◽  
Model Tests ◽  
The Past ◽  
Helical Strakes ◽  
Truss Spar ◽  
Computational Fluid Dynamics Cfd ◽  
Riser Design

Spar production systems are subject to Vortex Induced Motions (VIM) which may impact mooring and riser design. Helical strakes are employed to mitigate VIM. Model tests are typically required to validate the performance of the strakes. This paper will report on the results of benchmarking studies that have been conducted over the past few years to compare model tests with computational fluid dynamics (CFD). The paper discusses comparisons of CFD with model tests, “best practices” for the use of CFD for these classes of problems and issues related to turbulence modeling and meshing of problems at large Reynold’s numbers. This work is ongoing.

Drilling Riser Design and Analysis for Deepwater Applications

2013 ◽  
Author(s):  
Yongming Cheng ◽  
Tao Qi
Keyword(s):  
High Pressure ◽  
Production Systems ◽  
Dynamic Performance ◽  
Design Procedure ◽  
Dynamic Strength ◽  
Low Pressure ◽  
Strength Analysis ◽  
Global Dynamic ◽  
Analysis Methodology ◽  
Riser Design

A riser is a fluid conduit from subsea equipment to surface floating production systems such as spars, TLPs, and semi-submersibles. It is a key component in a drilling and producing system. Drilling risers include the applications in marine drilling (low pressure) and tie-back drilling (high pressure). This paper discusses drilling riser design and analysis for a deepwater application. This paper first discusses the configuration of marine drilling and tie-back drilling risers. It then presents the drilling riser design procedure and analysis methodology. The riser design and analysis cover the riser tensioner setting, marine operation window, strength and fatigue, etc. A marine drilling riser example is used in the paper to demonstrate the design and analysis for a deepwater application. This paper shows the dynamic strength analysis results for the riser. It then identifies governing locations for the riser design. A tie-back drilling riser example is also provided to illustrate its global dynamic performance. This paper finally discusses the design and analysis challenges of a drilling riser for a deepwater application.

Integrated Analysis of Mooring and Riser Systems for FPSO’s in Harsh Shallow Water Environments

2011 ◽  
Author(s):  
M. Martens ◽  
J. R. Whelan ◽  
Y. Drobyshevski
Keyword(s):  
Shallow Water ◽  
Time Domain ◽  
Integrated Approach ◽  
Integrated Analysis ◽  
Mooring System ◽  
South East Asia ◽  
Riser Design ◽  
Design Case ◽  
East Asia Region ◽  
Design Challenges

Shallow water mooring and riser systems for permanently turret moored FPSOs present significant design challenges. Many FPSOs, in particular in the South-East Asia region, are required to remain on-station in 100-year return period tropical revolving storm (typhoon) conditions. Extreme sea states combined with the restricted height of the water column generate large mooring loads and make it difficult to accommodate conventional riser configurations. Metocean conditions in such areas can be highly directional. This directionality can be exploited by undertaking an integrated mooring and riser design analysis. The critical interface between the mooring and riser systems is the turret offset and the associated turret heave. The conventional approach is to identify a single offset envelope for each design case, comprising the mooring system (intact or damaged) and FPSO condition (loaded or ballasted), which is then used in riser design. This paper presents a more developed approach, the integrated approach, which is based on conducting the mooring and riser analyses simultaneously for a common set of design cases. To exploit the directionality of the metocean conditions, an offset envelope for each governing metocean condition is calculated from time domain mooring simulations, followed by a parameterisation scheme. As a result, multiple turret offsets and associated metocean conditions and FPSO headings are identified which form a family of offsets for each compass octant of the environment. The integrated approach is applied to an example FPSO with an external turret supporting seven risers arranged in double wave tethered configuration. The drivers and advantages for selecting a particular riser configuration are discussed. It is shown how application of an integrated analysis approach leads to less conservative combinations for use in the riser design, and enables the development of a feasible riser system. An optimal mooring pattern, both leg make-up and orientation for riser layout, is also developed.

Global Performance of Floating Production Systems

2002 ◽  
Author(s):  
D.L. Garrett ◽  
J.F. Chappell ◽  
R.B. Gordon
Keyword(s):  
Production Systems ◽  
Global Performance

Research on the Coupling Effects Between Ship Motions and Sloshing

2014 ◽  
Author(s):  
Wenhua Zhao ◽  
Jianmin Yang ◽  
Longbin Tao ◽  
David White
Keyword(s):  
Coupling Effect ◽  
Wave Spectrum ◽  
Model Tests ◽  
Experimental Results ◽  
Ship Motions ◽  
Coupling Mechanism ◽  
Floating Platform ◽  
Coupling Effects ◽  
Band Limited ◽  
Vessel Motion

Floating Liquefied Natural Gas (FLNG) facilities, which are a new type of floating platform, have been developed as an alternative to long pipelines for the exploitation of stranded offshore fields. FLNG vessels will be subjected to very complicated and onerous sea states in some regions and very severe motion responses must be avoided. The vessel motion can induce internal tank sloshing, which can in turn affect the global motion response of the vessel. This coupling response is of great importance for the safe design and operation of FLNG facilities in real sea states. This paper investigates the coupling effect between FLNG roll motions and sloshing. Model tests are carried out for a section of an FLNG vessel containing a tank excited in roll by band-limited white noise waves. During the model tests, the FLNG model is ballasted with fresh water and equivalent steel ballast weights respectively, to quantify the coupling effects due to the internal sloshing. Time histories of the global motions and the internal sloshing oscillations have been measured. Statistical and spectral analyses have been carried out on the measured data. The response amplitude operators are obtained using measured motion spectra divided by the excitation wave spectrum. The influence of the internal sloshing on the global motions has been illustrated through the comparison of the experimental results between the liquid and solid (steel) ballast weight cases. Based on the experimental results, some conclusions regarding the coupling mechanism between FLNG motions and sloshing are drawn.

Vortex-Induced Vibration of a Free-Hanging Riser Under Irregular Vessel Motion

2016 ◽  
Author(s):  
Jungao Wang ◽  
Rajeev Kumar Jaiman ◽  
Peter Francis Bernad Adaikalaraj ◽  
Linwei Shen ◽  
Sue Ben Tan ◽  
...  
Keyword(s):  
Literature Review ◽  
Experimental Validation ◽  
Ocean Current ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Norwegian Sea ◽  
Irregular Wave ◽  
Riser Design ◽  
Similarities And Differences ◽  
Vessel Motion

In this paper, we focus on vortex-induced vibration (VIV) of a free-hanging riser attached to a vessel under irregular wave conditions. The global in-plane responses of the hanging riser are firstly studied numerically in order to generate the equivalent current profile under vessel motion, and a simplified irregular vessel motion-induced VIV prediction methodology is then proposed based on the understanding from previous experimental observations and literature review. Further comparison on irregular vessel motion-induced VIV and ocean current-induced VIV at the same operation site with the same return period is performed to emphasize the importance of vessel motion-induced VIV. Numerical results highlight that vessel motion-induced VIV can cause similar stresses, fatigue damage and drag amplification similar to the steady ocean current cases, especially to the operation site like Norwegian Sea where strong wave field exists with mild current condition. It should be mentioned that although the simplified methodology proposed in this paper requires further experimental validation, it is believed that the presented numerical pre-study would help the industry and the researchers to have initial understanding on the possible occurrence of vessel motion-induced VIV. We further show the similarities and differences of vessel motion-induced VIV with respect to the ocean current-induced VIV and its implications on riser design and operation.

New Frontiers in the Design of Steel Catenary Risers for Floating Production Systems

2001 ◽  
Vol 123 (4) ◽  
pp. 153-158 ◽  
Author(s):  
Basim B. Mekha
Keyword(s):  
New Technologies ◽  
Production Systems ◽  
Random Wave ◽  
Environmental Loads ◽  
Steel Catenary Riser ◽  
Field Development ◽  
Steel Catenary Risers ◽  
Motion Characteristics ◽  
Vessel Motion ◽  
Water Depths

The steel catenary riser (SCR) concept has recently been used in almost every new deepwater field development around the world. Shell pioneered the implementation of the SCR concept in 1994 on its Auger tension leg platform (TLP) in 872 m (2860 ft) water depth. Since then, SCRs have been vital to deepwater field developments. Their use has given a new dimension to oil exploration and transportation in water depths where other riser concepts could not tolerate the environmental loads or would have become very costly. SCR designs are very sensitive to floating support platform or vessel motion characteristics to which they are typically attached. In addition to pipe stresses, the main design issue for the SCR concept is fatigue related. There are two main sources for fatigue: random wave fatigue and vortex-induced vibration (VIV) fatigue. The former is due to wave action and the associated platform motion characteristics. The VIV fatigue is mainly due to current conditions. Fracture mechanics assessment is also an essential issue that must be addressed in the design of SCRs. This paper presents a brief history in the use and development of SCRs since the first project implementation on Auger TLP in 1994. The paper also summarizes major steps that must be considered in the design of SCRs and how to explain their behavior in different water depths and environmental conditions. Existing design boundaries for SCRs are discussed with emphasis on the capabilities of new technologies that enable engineers to go beyond these boundaries. Projects with unique SCR features and their implementation are compiled and presented.

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