On the Wave and VIV Fatigue of Steel Catenary Risers Connected to Floating Structures

2002 ◽  
Author(s):  
Basim B. Mekha
Keyword(s):  
Fatigue Damage ◽  
Random Wave ◽  
Pipeline System ◽  
Floating Structure ◽  
Drift Motion ◽  
Steel Catenary Riser ◽  
Slow Drift ◽  
Response Amplitude Operators ◽  
Motion Characteristics ◽  
Vessel Motion

The Steel Catenary Riser (SCR) concept has been considered as a vital option for most new deepwater field developments around the world. The use of an SCR, as a pipe connecting the export pipeline system and/or remote wells and infield flowline to a floating structure, has given more flexibility and potential to the oil exploration and transportation in water depths where other riser concepts would not tolerate the hydrostatic loads or would have become very costly. Major design concerns of the SCR pipes connected to a floating structure are the dynamic motion and the fatigue damage. The SCRs are very sensitive to the platform or vessel motion characteristics to which they would be attached as well to the environmental loads. The two main sources of fatigue are the random wave sea states and the associated platform motion and vortex induced vibration (VIV) due to current. The wave sea states are represented by wave spectra while the platform motions are applied as first order Response Amplitude Operators (RAOs) and second order slow drift motions. This paper gives a brief introduction about the development of the fatigue analysis methods that have been used to date. Results of parametric studies investigating several effects on the fatigue damage of the SCRs are presented. Some of these effects include flexible joint rotational stiffness, VIV analysis parameters, slow drift motion effects. The results will be for different size risers and fluid contents.

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.

Time Domain Computation of Riser VIV From Vessel Motions

2006 ◽  
Author(s):  
Yongming Cheng ◽  
Kostas F. Lambrakos
Keyword(s):  
Velocity Profile ◽  
Fatigue Damage ◽  
Time Domain ◽  
Relative Velocity ◽  
Structural Characteristics ◽  
Time Domain Analysis ◽  
Computer Time ◽  
Steel Catenary Riser ◽  
Vessel Motion ◽  
Time Invariant

Intermittent riser VIV behavior caused by vessel motions can affect both riser strength and fatigue life. There are frequency domain codes available that are used routinely to calculate riser fatigue damage from VIV due to currents. These codes are often adapted to calculations of the vessel motion VIV and fatigue damage. The adaptations reduce the intermittent VIV to steady state VIV by assuming an appropriate time invariant velocity profile over the length of the riser. However, since vessel motions cause a relative velocity profile over the riser that varies with time, and the VIV response is intermittent, a time domain VIV code is best suited for such an analysis. The paper demonstrates the use of Technip’s time domain riser VIV code ABAVIV to calculate steel catenary riser VIV response and fatigue damage due to vessel motions. Since time domain analysis is computer time intensive, the paper also outlines an efficient methodology to perform these calculations. The analysis example in the paper is based on surge, pitch, and heave motions which are the most important vessel motions for the riser fatigue damage near the touch down region. The ABAVIV code accounts for the nonlinear structural characteristics of the SCR, and the unsteadiness of the VIV phenomenon for the present application.

scholarly journals Time Domain Simulation of Slow Drift Motion of a Floating Structure in Waves

1989 ◽  
Vol 1989 (166) ◽  
pp. 151-162
Author(s):  
Takeshi Kinoshita ◽  
Kazuhito Takaiwa ◽  
Takahiro Murakami ◽  
Koichi Masuda
Keyword(s):  
Time Domain ◽  
Time Domain Simulation ◽  
Floating Structure ◽  
Drift Motion ◽  
Slow Drift ◽  
Slow Drift Motion

Multi-Pronged Approach for the Design of HP/HT Deepwater Steel Catenary Risers

2019 ◽  
Author(s):  
Gurudutt Bangalore ◽  
Yongming Cheng ◽  
Surya Banumurthy
Keyword(s):  
Problem Solving ◽  
Wall Thickness ◽  
Pipe Wall ◽  
Steel Catenary Riser ◽  
Riser Pipe ◽  
Successful Design ◽  
Steel Catenary Risers ◽  
Grade Material ◽  
Motion Characteristics ◽  
Vessel Motion

Abstract As the industry plans to move forward with the development of high pressure and high temperature (HP/HT) fields, challenges exist for the design of complaint risers in deepwater applications. The conventional wet tree application risers such as Steel Catenary Risers (SCRs) have proven to be mature technologies in the deepwater applications around the world. HP/HT application leads to many challenges in deepwater risers. This paper investigates ways to overcome the design challenges of deepwater SCRs using a multi-pronged approach. The paper first addresses the challenge in riser pipe wall thickness. The HP/HT applications require higher pipe wall thicknesses mainly governed by the burst pressure design requirements. The pipe wall thicknesses required for the HP/HT applications will result in very high installation loads, reeling issues with low D/t, fabrication (welding) challenges, high payloads to the host vessel, etc. Any optimization to the wall thickness design in terms of using higher grade material, advancements in welding technology and advantages to be gained in the use of design codes can potentially help in overcoming of these challenges. The pipe sizes used in the HP/HT applications can pose significant challenges to the touchdown zone (TDZ) of standard steel catenary riser configurations, in terms of experiencing large TDZ compressions and having fatigue life concerns. Use of different SCR problem-solving approaches — TDZ clump weights, Lazy Wave Steel Riser (SLWR) and weight optimized risers will be reviewed in this paper. Vessel motion characteristics can significantly affect the riser performance. Vessels with improved motions, particularly from the riser response viewpoint, can play a significant role in the selection of optimum riser configurations. This has to be achieved in the early stages of the project. Some of the work done recently in development of the optimized vessel performance particularly in the case of semi-submersibles and their implications on the riser design are studied in this paper. Design of the risers in HP/HT fields in deepwater applications presents significant challenges and requires a multi-dimensional problem solving approach. An example is provided in this paper for the investigation. A multi-pronged approach has to be adopted for the successful design of riser system for HP/HT deepwater applications.

scholarly journals Research on Hydroelastic Response of an FMRC Hexagon Enclosed Platform

Symmetry ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1110
Author(s):  
Wei-Qin Liu ◽  
Luo-Nan Xiong ◽  
Guo-Wei Zhang ◽  
Meng Yang ◽  
Wei-Guo Wu ◽  
...  
Keyword(s):  
Time Domain ◽  
Numerical Models ◽  
Structural Response ◽  
Deep Ocean ◽  
Surface Model ◽  
Large Area ◽  
Floating Structure ◽  
Small Depth ◽  
Response Amplitude Operators ◽  
Hydroelastic Response

The numerical hydroelastic method is used to study the structural response of a hexagon enclosed platform (HEP) of flexible module rigid connector (FMRC) structure that can provide life accommodation, ship berthing and marine supply for ships sailing in the deep ocean. Six trapezoidal floating structures constitute the HEP structure so that it is a symmetrical very large floating structure (VLFS). The HEP has the characteristics of large area and small depth, so its hydroelastic response is significant. Therefore, this paper studies the structural responses of a hexagon enclosed platform of FMRC structure in waves by means of a 3D potential-flow hydroelastic method based on modal superposition. Numerical models, including the hydrodynamic model, wet surface model and finite element method (FEM) model, are established, a rigid connection is simulated by many-point-contraction (MPC) and the number of wave cases is determined. The load and structural response of HEP are obtained and analyzed in all wave cases, and frequency-domain hydroelastic calculation and time-domain hydroelastic calculation are carried out. After obtaining a number of response amplitude operators (RAOs) for stress and time-domain stress histories, the mechanism of the HEP structure is compared and analyzed. This study is used to guide engineering design for enclosed-type ocean platforms.

ECA Methodology for Fatigue Design of Risers and Flowlines

2007 ◽  
Author(s):  
C. H. Luk ◽  
T. J. Wang
Keyword(s):  
Fracture Mechanics ◽  
Design Method ◽  
Steel Catenary Riser ◽  
Fatigue Design ◽  
Wide Range ◽  
Fatigue And Fracture ◽  
Level 3 ◽  
Fatigue Loads ◽  
Vessel Motion ◽  
Level 2

Engineering Criticality Assessment (ECA) is a procedure based on fracture mechanics that may be used to supplement the traditional S-N approach and determine the flaw acceptance and inspection criteria in fatigue and fracture design of risers and flowlines. A number of design codes provide guidance for this procedure, e.g. BS-7910:2005 [1]. However, more investigations and example studies are still needed to address the design implications for riser and flowline applications. This paper provides a review of the existing ECA methodology, presents a fracture mechanics design method for a wide range of riser and flowline fatigue problems, and shows flaw size results from steel catenary riser (SCR) and flowline (FL) examples. The first example is a deepwater SCR subjected to fatigue loads due to vessel motion and riser VIV. The second example is a subsea flowline subjected to thermal fatigue loads. The effects of crack re-characterization and material plasticity on the Level-2 and Level-3 ECA results of the SCR and flowline examples are illustrated.

Sensitivity Study of Critical Parameters Influencing the Uncertainty of Fatigue Damage in Steel Catenary Risers

2010 ◽  
Author(s):  
Feng Zi Li ◽  
Ying Min Low
Keyword(s):  
Fatigue Damage ◽  
Cost Effective ◽  
Sensitivity Study ◽  
Structural Safety ◽  
Critical Parameters ◽  
Design Parameters ◽  
Steel Catenary Riser ◽  
Bending Stresses ◽  
Steel Catenary Risers ◽  
Touchdown Point

The most challenging aspect of a deepwater development is the riser system, and a cost-effective choice is the Steel Catenary Riser (SCR). Fatigue is often a governing design consideration, and it is usually most critical at the touchdown point (TDP) where static and dynamic bending stresses are highest. Unfortunately, it is also at this region that uncertainty is the maximum. The increased uncertainty casts doubt on the applicability of generic safety factors recommended by design codes, and the most consistent way of ensuring the structural safety of the SCR is to employ a reliability-based approach, which has so far not received attention in SCR design. As the number of basic random variables affects the complexity of a reliability analysis, these variables should be selected with caution. To this end, the aim of this paper is to draw up a comprehensive list of design parameters that may contribute meaningfully to the uncertainty of the fatigue damage. From this list, several parameters are selected for sensitivity studies using the commercial package Orcaflex. It is found that variations in seabed parameters such as soil stiffness, soil suction and seabed trench can have a pronounced influence on the uncertainty of the fatigue damage at the touchdown point.

An Investigation into the Motion Behaviour of a Wind Farm Mothership

2015 ◽  
Author(s):  
Blanca Peña ◽  
Erik P. ter Brake ◽  
Kyriakos Moschonas
Keyword(s):  
Numerical Simulations ◽  
Wind Farm ◽  
Wind Farms ◽  
Weather Conditions ◽  
Offshore Wind ◽  
Financial Benefit ◽  
Offshore Wind Farms ◽  
Motion Characteristics ◽  
Vessel Motion ◽  
Motion Behavior

A number of UK Round Three offshore wind farms are located relatively far from the coast making crew transfer to the sites time consuming, more prone to interruption by weather conditions and increasingly costly. In order to optimize the functionality of a permanent accommodation vessel, Houlder has developed a dedicated Accommodation and Maintenance Wind Farm vessel based on an oil & gas work-over vessel that has been successfully deployed for many years. The Accommodation and Maintenance (A&M) Wind Farm vessel is designed to provide an infield base for Marine Wind Farm operation. The A&M vessel is designed for high operability when it comes to crew access and performance of maintenance and repair of wind turbine components in its workshops. Also general comfort on board is of high regard. As such, the seakeeping behavior of the unit is of great importance. In this publication, the seakeeping behavior is presented on the basis of numerical simulations using 3D diffraction software. The first design iteration is driven by achieving high maneuverability and good motion characteristics for operational up-time and personnel comfort on board the vessel. Model test data of the original work-over vessel has been used to validate and calibrate the numerical simulations. On this basis, parametric studies can be performed to fine-tune a potential new hull form. In turn, this could reduce the number of required physical model tests providing a potential financial benefit and optimized delivery schedule. The vessel motion behavior was tested against the acceptability criteria and crew comfort guidelines of motion behavior for a North Sea environment.

Sign in / Sign up

Export Citation Format

Share Document