The Effect of the Sea-Bottom Proximity on the Fatigue Life of Suspended Spans of Offshore Pipelines Undergoing Vortex-Induced Vibrations

1982 ◽  
Author(s):  
Demos T. Tsahalis ◽  
Warren T. Jones
Keyword(s):  
Fatigue Life ◽  
Offshore Pipelines ◽  
Sea Bottom ◽  
Vortex Induced Vibrations

The Effect of Seabottom Proximity of the Vortex-Induced Vibrations and Fatigue Life of Offshore Pipelines

1983 ◽  
Vol 105 (4) ◽  
pp. 464-468 ◽  
Author(s):  
D. T. Tsahalis
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Experimental Results ◽  
Offshore Pipelines ◽  
Vortex Induced Vibrations

The effect of the seabottom proximity on the vortex-induced vibrations of suspended spans of offshore pipelines is discussed in the light of recent relevant experimental results. It is shown that the effect of the seabottom proximity is to drastically alter the vortex-induced vibrations of supsended spans resulting into longer fatigue lives or equivalently longer safe lengths. A “generalized” fatigue damage is formulated universally applicable to all suspended spans.

Impact—Response Behavior of Offshore Pipelines

1982 ◽  
Vol 104 (4) ◽  
pp. 325-329 ◽  
Author(s):  
P. G. Bergan ◽  
E. Mollestad
Keyword(s):  
Plastic Material ◽  
Material Behavior ◽  
Hydrodynamic Drag ◽  
Offshore Pipelines ◽  
Sea Floor ◽  
Drag Forces ◽  
Sea Bottom ◽  
Nonlinear Dynamic Equations ◽  
Numerical Formulation ◽  
Inertia Forces

A method for analyzing the dynamic behavior of marine pipelines subjected to impact loads or sudden forced movements is outlined. Inertia forces (also from hydrodynamic mass), hydrodynamic drag forces as well as friction and lift effects for a pipe at the sea bottom are accounted for. An extensive nonlinear formulation is used for the pipe itself; it includes large displacements and elasto-plastic material behavior. Aspects of the numerical formulation of the problem and the solution of the nonlinear dynamic equations are discussed. The examples show computed dynamic response for pipelines lying on the sea floor and for a pipe section freely submerged in water when subjected to various force and displacement histories.

On Remaining Fatigue Life Fracture Mechanics Analysis of Free-Spanning Pipelines Using Shell and Line-Spring Elements

2002 ◽  
Author(s):  
F. Redaelli ◽  
B. Skallerud ◽  
B. J. Leira
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Cross Flow ◽  
Finite Element Program ◽  
Shell Elements ◽  
Cyclic Stresses ◽  
Vortex Induced Vibrations ◽  
Element Program ◽  
Remaining Fatigue Life

The present paper addresses fatigue crack-growth for free-spanning pipelines. The main sources of cyclic stresses which cause the crack-growth are vortex-induced vibrations (VIV) of the pipeline in the cross-flow and in-line directions. In the presence of initial weld defects, such cyclic stresses may lead to leakage and sudden fracture. The crack-growth process is modelled using so-called line-spring elements. These are matched with shell elements which are applied for modelling the pipe itself. The crack-growth is simulated by performing several simulations with different crack sizes. The shape of the crack also allowed to vary during the growth (i.e a/c-ratio). The static equilibrium position of the pipeline for a specific free span is first established by the non-linear Finite Element program ABAQUS. The line-spring elements are matched to interface with the shell elements which represent the pipe outside the region where the crack is located. Based on such simulations, the stress intensity factors at the crack-tip are computed. These calculations are performed for several different crack-sizes. Finally, the remaining fatigue life is estimated by means of fracture mechanics in terms of analytical and semi-empirical approaches.

Fatigue Calculation of Risers Using a Van Der Pol Wake Oscillator Model With Random Parameters

2008 ◽  
Author(s):  
Yahya Modarres-Sadeghi ◽  
Franz S. Hover ◽  
Michael S. Triantafyllou
Keyword(s):  
Fatigue Life ◽  
Standing Wave ◽  
Oscillator Model ◽  
Random Parameters ◽  
Van Der Pol ◽  
Sheared Flow ◽  
Wake Oscillator Model ◽  
Model Scale ◽  
Wake Oscillator ◽  
Vortex Induced Vibrations

Vortex induced vibrations of long distributed structures (risers and mooring cables) is an inherently complicated phenomenon in which due to the riser multi-mode excitations, various combinations of traveling and standing wave patterns along the length is observed. These observations are made based on a series of model scale experiments conducted on a riser for both uniform and linearly sheared flow cases. In these model scale experiments, strain and acceleration measurements are conducted at selected points along the riser. The contour plots of amplitudes of oscillations in these experiments show a mainly traveling wave behavior for linearly sheared flow cases and a mainly standing wave one for the uniform flow cases. In order to model the vortex induced vibrations of the riser used in these experiments, a wake oscillator model is used. In this model, the riser is assumed to be a tensioned string and the wake dynamics is represented by a Van der Pol oscillator whose driving force is in parallel with the riser acceleration. Randomness in the current, added mass and lift coefficients is taken into account by considering random parameters for the wake oscillator model. By using the proper parameters in this wake oscillator model, its results can be compared with the experimental ones. The comparison is made in terms of dynamical behavior (traveling waves versus standing waves, amplitudes and frequencies of oscillations) as well as the fatigue life calculations. The statistics of fatigue life calculations based on the experimental reconstruction compares well with those of the model results showing that the theoretical model can predict fatigue damage of the riser fairly well.

Vortex-Induced Vibrations of Long Marine Risers in Sheared Flows: DNS Studies

2003 ◽  
Author(s):  
Didier Lucor ◽  
X. Ma ◽  
M. S. Triantafyllou ◽  
G. E. Karniadakis
Keyword(s):  
Fatigue Life ◽  
Floating Structures ◽  
Marine Risers ◽  
Sheared Flows ◽  
Vortex Induced Vibrations ◽  
Offshore Industry ◽  
Water Depths

The offshore industry is moving to ever-increasing water depths, producing presently oil in depths of up to 2,500m, requiring detailed fatigue calculations for the risers and tendons used in the floating structures, see [1, 2]. Currents in the ocean are invariably highly sheared, hence the modes that can potentially be excited are many, see [3]. The calculation of how many and which modes are excited, can affect fatigue life very significantly, but there are no guidelines presently available for conducting this calculation.

Effect of Damping on VIV Response in Umbilicals and Flexible Risers

2015 ◽  
Author(s):  
Kay Hansen-Zahl ◽  
Veronica Henøen ◽  
Rolf Baarholm ◽  
Farzan Parsinejad ◽  
Yiannis Constantinides
Keyword(s):  
Fatigue Life ◽  
Internal Pressure ◽  
Contact Force ◽  
Damping Ratio ◽  
Life Assessment ◽  
Stick Slip ◽  
Modal Damping Ratio ◽  
Modal Damping ◽  
Vortex Induced Vibrations ◽  
Flexible Risers

The fatigue life assessment of umbilicals and flexible risers due to vortex-induced vibrations (VIV) require special attention to the structural properties of the flexible bundle due to stick/slip behavior of helical elements in bending. The VIV response on umbilicals and flexible risers is complex, and it is controlled by several parameters. Structural damping is one of these parameters, but this is typically calculated based on the material damping of the structure. Similar to flexible risers and umbilicals, hysteresis damping due to the stick/slip behavior in the helical layers may be significant for cable structures. The purpose of this study is to evaluate the effect of the hysteresis damping on VIV response, and to demonstrate a procedure for consistent VIV fatigue analysis of flexible risers and umbilicals. The stick/slip hysteresis varies with varying contact force, and the contact force is dependent on internal pressure and effective tension. The effect of varying these parameters is included in the study. Furthermore, the study includes different riser system configurations and current profiles. In this paper, the stick/slip hysteresis has been established for two umbilicals and two flexible risers, with varying internal pressure and effective tension. Combined with five different configurations (both shallow and deep water) and 16 different current profiles, the VIV modes have been calculated and the corresponding stick/slip modal damping ratio has been established. Finally, using fatigue current profiles, fatigue life estimates have been made based on different damping ratios, including the estimated stick/slip damping ratio. The study presented in this paper has been carried out as part of the Norwegian Deepwater Programme (NDP).

Alternative Method of Buoy Supporting Riser (BSR) Installation

2011 ◽  
Author(s):  
Ricardo Franciss ◽  
Enrique Casaprima Gonzales ◽  
Jose´ Carlos Lima de Almeida ◽  
Jairo Bastos de Arau´jo ◽  
Antonio Carlos Fernandes
Keyword(s):  
Fatigue Life ◽  
Field Test ◽  
Water Depth ◽  
Monitoring Systems ◽  
Deep Waters ◽  
Alternative Method ◽  
Sea Bottom ◽  
Campos Basin ◽  
Steel Catenary Risers ◽  
Flexible Risers

Due to the 2200m water depth and harsher environmental conditions, one option that Petrobras is considering for the production of the Pre-Salt fields is the use of a subsurface buoy known as a Buoy Supporting Riser (BSR). It is composed of a subsurface tethered buoy, flexible jumpers connecting the Floating Production Unit (FPU) to the BSR and Steel Catenary Risers (SCRs) connecting the BSR to the flowlines on the sea bottom. The main advantages of this system are that it decouples the FPU motions from the SCRs, reducing fatigue damage in the touch down zone. It may also be installed independently of the FPU, except for the flexible jumpers, which would reduce the risers load on the FPU. Petrobras has been studying this concept since 1997 and has established, as a final stage of the study, a field test with the actual installation of the BSR. This was performed through an alternative method using only Petrobras AHTS boats, in order to avoid critical and expensive resources such as lift barges. With the purpose of validating this new installation procedure, Petrobras performed the referred installation of a 27.2m × 27.2m square ring shaped buoy in Congro Field in the Campos Basin over a water depth of 500m. The buoy was positioned at 80m depth, where the incidence of loads caused by waves is negligible, thus increasing the fatigue life of risers. After the BSR installation, the riser pull-in procedure was also conduced. This paper describes why this technology is necessary for these fields and the model tests made to validate the installation procedures. It also discusses how Petrobras tested the pull-in operations for two flexible risers after the actual buoy was installed. Monitoring systems were designed to check all forces and displacements during the referred installation. These actions will consolidate the BSR technology for Petrobras leading to another riser system option for production in ultra deep waters.

Experiences Using DNV-RP-F105 in Assessment of Free Spanning Pipelines

2005 ◽  
Author(s):  
Olav Fyrileiv ◽  
Kim Mo̸rk ◽  
Muthu Chezhian
Keyword(s):  
Fatigue Life ◽  
Research And Development ◽  
Design Methodology ◽  
Cost Effective ◽  
Design Phase ◽  
Vortex Induced Vibrations ◽  
Operational Phase ◽  
Pipeline Failures ◽  
Analytical Tools ◽  
Pipeline Design

Free spans often become a challenge in pipeline design and operation due to pipeline installation on uneven seabed or seabed scouring effects. The costs related to seabed correction and span intervention are in many projects considerable. Therefore it is relevant to investigate whether such intervention work is necessary or not. Despite the complexity inherent in free span response, the spans are often designed applying presumably conservative concepts and very simple analytical tools. The DNV guideline no 14 (GL14) for free spanning pipelines was issued in 1998 and has later been updated and issued as an Recommended Practice (DNV-RP-F105) to account for recent technical research and development and accumulated experience applying GL14 in pipeline projects. This code allows vortex induced vibrations (VIV) as long as the pipeline integrity is ensured, by for example checking that the fatigue life is sufficient. By giving design methodology and acceptance criteria for fatigue, the DNV-RP-F105 approaches the real physics of free spans in a better way than older codes and makes it possible to select cost-effective methods both in the design phase and later when re-assessing spans in the operational phase. This paper will briefly discuss some experiences obtained by using the DNV-RP-F105 in free span design/re-assessment. Some examples of pipeline failures due to free span and vortex induced vibrations will also be presented.

A Review of VIV Responses of Steel Lazy Wave Riser

2016 ◽  
Author(s):  
Airindy Felisita ◽  
Ove T. Gudmestad ◽  
Daniel Karunakaran ◽  
Lars Olav Martinsen
Keyword(s):  
Fatigue Life ◽  
Water Depth ◽  
Lower Cost ◽  
Fatigue Lifetime ◽  
Hydrocarbon Content ◽  
Vortex Induced Vibrations ◽  
Norwegian Continental Shelf ◽  
Arch Shape ◽  
Current Exposure ◽  
Observation Results

The Steel Lazy Wave Riser (SLWR) configuration is considered as one of the favorable solutions for deepwater applications. This is due to the SLWR’s capability to effectively absorb the dynamic motions from the vessel and the relatively lower cost that it offers. However, the application of SLWRs has its own challenges when it comes to fatigue due to Vortex-Induced Vibrations (VIV). The buoyancy section and the touchdown area may be critical to VIV due to curvature and current exposure onto the area. Furthermore, there is only limited previous research on VIV responses of a SLWR configuration. This paper presents a parametric study of VIV responses of various SLWR systems. The study location is the deeper area of the Norwegian Continental Shelf. The main parametric variations are water depth, the length of the buoyancy section, the dimension of the buoyancy modules and the hydrocarbon content. These variations result in different lazy wave configurations, which give different trends of VIV responses. The analysis works are performed using the computer programs Riflex and VIVANA. The observation results show that, for the type of current used in this study, riser configurations at the same water depth tend to have the same level of fatigue life. In addition, risers in shallower water have a lower fatigue life compared to risers in deeper water due to the current profiles used in this study and the higher system stiffness of the risers at shallower water. The results also show that the buoyant section has only little to modest influence on the VIV-fatigue life. The influence will only become apparent when the buoyancy section creates a sufficiently high arch shape in the lazy wave configuration. The riser’s selfweight mainly affects the riser’s fatigue life at the upper catenary part of the riser. Although the upper catenary part of the riser generally has sufficient VIV-fatigue lifetime, a riser with lighter content has a lower fatigue life at this part compared to a riser with heavier content.

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