VIV Response of Long Free Spanning Pipelines (original) (raw)
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Evaluation of Vortex Induced Vibration Effective Parameters on Free-Span Subsea Pipelines
International Journal of coastal and offshore engineering, 2019
Subsea pipelines due to the reduction of transfer costs and expedite the offshore operations is one of the all-purpose structures in marine industries. Subsea pipelines are exposed to a variety of hazards, including corrosion and fatigue Etc. Free span exacerbates the fatigue required parameters due to a phenomenon called the Vortex Induced Vibration (VIV). In this research, the influence of the span's length on the free span subsea pipeline has been reviewed with ABAQUS standard code. In this study the previous result has been expanded. The results of the VIV fatigue life are extensible to all of the depth. Achieved Results indicate that the fatigue life of the pipeline even in the worst condition is much higher than the required amount that it represents the upstream design of DNV-RP-F105. In this study the backrest pipeline has been investigated and result show that the pipeline under the different conditions in the backrest, by creating more vibration and displacement on one side of the pipeline reduces the fatigue life of 113 percent compared to snap. The VIV fatigue life has undergone a lot of changes due to span length changes, maximum changes occur between cable and behavioral which the amount of these changes is reduced by 75%. The free span length is another factor in VIV fatigue. VIV fatigue life will be increased by reducing the span length. As well as increasing the flow velocity that is the main factor in creating the VIV is increased fatigue. Therefore, in terms of the accuracy in the choice of the existing conditions of very high importance for the pipeline. Comparison between effect parameters in VIV fatigue life was shown that span length is the most effective parameter.
VIV Analysis of Pipelines Under Complex Span Conditions
Journal of Marine Science …, 2009
Spans occur when a pipeline is laid on a rough undulating seabed or when upheaval buckling occurs due to constrained thermal expansion. This not only results in static and dynamic loads on the flowline at span sections, but also generates vortex induced vibration (VIV), which can lead to fatigue issues. The phenomenon, if not predicted and controlled properly, will negatively affect pipeline integrity, leading to expensive remediation and intervention work. Span analysis can be complicated by: long span lengths, a large number of spans caused by a rough seabed, and multi-span interactions. In addition, the complexity can be more onerous and challenging when soil uncertainty, concrete degradation and unknown residual lay tension are considered in the analysis. This paper describes the latest developments and a 'state-of-the-art' finite element analysis program that has been developed to simulate the span response of a flowline under complex boundary and loading conditions. Both VIV and direct wave loading are captured in the analysis and the results are sequentially used for the ultimate limit state (ULS) check and fatigue life calculation.
A Comparative Study of a Free Span Pipeline Through Numerical Simulations
Volume 6B: Pipeline and Riser Technology, 2014
A subsea pipeline has an important role to produce oil and gas from an offshore petroleum field, connecting a petroleum facility at the open sea and a near shore terminal at the coast. Very often, the pipeline passes over areas with uneven seafloor, and it may present free span portions. The main aim of the present work is improvements on the understanding of undesirable effects of vibrations in a subsea pipeline which presents free span portions along its length. This understanding is fundamental for the safe design and operation of the pipeline with possible reduction of its fatigue life. Dynamic loads can occur as a consequence of the presence of sea currents acting on portions of the pipeline with free spans. Due to this hydrodynamic current loads, the pipeline structure may oscillate in the same direction of the current (Inline) and, in its transverse direction (Cross-Line). This dynamic response at the free span is mainly caused by the Vortex Induced Vibration (VIV). It is very important for the pipeline design because it can result extreme unacceptable stresses as well as in exceeding limits for the fatigue damage of the pipeline. And, this problem of VIV is still not been completely understood. In the present paper, different models to estimate VIV forces due to sea current are discussed. For this purpose, different computer programs were used to predict vibrations in the transverse direction of the current incidence direction, caused by the vortex shedding in a free span of the pipeline. Simulations of the dynamic behavior of a free span portion of the pipeline were carried out by two approaches, respectively: an empirical hydrodynamic VIV force model, in frequency domain and, a semi-empirical VIV force model based on the lift coefficient and Strouhal number, in time domain. Simulations results are analyzed through comparisons with experimental data and also limitations of the each model are discussed.
Dynamic behavior of pipelines and risers due to vortex-induced vibration in time domain
Marine Systems & Ocean Technology, 2011
Vortex-Induced Vibration (VIV) plays an important role in the design of oil and gas production systems in offshore pre-salt fields in Santos Basin, Brazil. The importance is represented by the large depth ofpetroleum reservoirs bellow the subsalt layer, the ultra-deep waterdepth and the far distance ofthe oilfield from the coast. Very aggressive fluid components like C02 and S02 present in the produced petroleum make more complex the necessities in terms of material properties for pipelines and risers, which will increase problems due to the fatigue. The VIV in otfshore structures is complex and still not been completely understood, particularly for current with high Reynolds number (Re). This paper describes a time domain simulation ofthe dynamics ofpipeline and risers subjected to VIV. A semi-empirical model is adopted to calculate the cross-flow force due to VIV based on the lift coefficient and Strouhal number. This force is evaluated by a Morison-type formulation. The flow is assumed two-dimensional and the shedding frequency is not locked on to the structure vibrating frequency. The proposed simulation model is validated through comparisons ofits results with experimental data.
Dominant parameters for vortex-induced vibration of a steel catenary riser under vessel motion
Ocean Engineering
Recent research has confirmed a new type of vortex-induced vibration (VIV) in steel catenary risers (SCRs), purely caused by vessel motion. Vessel motion-induced VIV occurs because the SCR is exposed to the equivalent oscillating current due to its own motions relative to the still water. Preliminary results indicate that vessel motion-induced VIV is quite different from ocean current-induced VIV and is characterized with distinct time-varying features. In the present study, we aim at further summarizing the dominant parameters that govern the general vessel motion-induced VIV responses. Throughout the comparative studies on the instantaneous and statistical VIV responses including strain, displacement, response frequency, fatigue damage and top tension variation, the maximum Keulegan-Carpenter number max KC and the maximum equivalent current velocity V n_max are found to be the two dominant parameters that govern the vessel motion-induced VIV responses. Generally speaking, when max KC is sufficiently large
The present study provides original results of an experimental approach to understand the VIV phenomenon on long flexible cylinders launched in catenary configuration. The tests were carried out in a towing tank by means of a movable floor attached to the carriage car. Three groups of tests were considered, comprising the incidence of uniforme current profiles in catenary arrangements transverse and longitudinal to the inflow, the second one tested in two different directions. The catenary models were built by means of silicone tubes fulfilled with steel microspheres leading to achieve a mass ratio of m * = 3.72. Displacements along the models were measured by means of an underwater image tracking system and a large number of passive targets along the lines. A Galerkin's modal decomposition scheme is applied to obtain the modal-amplitude time histories and then the root-mean-square amplitudes as functions of the modal reduced velocities. Curiously, the modal results are quite characteristic of simpler systems with low m * , particularly in terms of the synchronization behavior observed in VIV reponses of rigid cylinders elastically supported. The modal decomposition procedure , therefore, is presented as a great technique for improvement of the investigations concerning the VIV of long flexible lines, revealing interesting results not yet observed experimentally in a so accurate way.
Experimental Evaluation of Vortex Induced Vibration Response of Straked Pipes in Tandem Arrangements
Volume 5: Ocean Engineering; CFD and VIV, 2012
Vortex induced vibration (VIV) due to steady current flow can be a significant driver in the design of offshore riser systems, affecting riser global configuration, component details and overall subsea architecture. Helical strakes are known to reduce VIV but the degree of effectiveness can vary considerably depending on strake pitch, fin height and more importantly, current flow regime. In addition, the amplitude of VIV and the effectiveness of VIV suppression strakes depends on the inclination of flow to the riser (incidence angle) and presence of wake effects from adjacent risers. Test and field data regarding suppression of riser VIV by strakes is not extensively available in the public domain. This is primarily due to the proprietary nature of the tests conducted in industry. In this paper, a program of testing is devised to better understand strake effectiveness as a function of current incidence angle and the presence of adjacent risers. Experiments have been conducted on sin...
2016
The present study provides original results of an experimental approach to understand the VIV phenomenon on long flexible cylinders launched in catenary configuration. The tests were carried out in a towing tank by means of a movable floor attached to the carriage car. Three groups of tests were considered, comprising the incidence of uniforme current profiles in catenary arrangements transverse and longitudinal to the inflow, the second one tested in two different directions. The catenary models were built by means of silicone tubes fulfilled with steel microspheres leading to achieve a mass ratio of m∗ = 3.72. Displacements along the models were measured by means of an underwater image tracking system and a large number of passive targets along the lines. A Galerkin’s modal decomposition scheme is applied to obtain the modal-amplitude time histories and then the root-mean-square amplitudes as functions of the modal reduced velocities. Curiously, the modal results are quite charact...
Insights on the design of free-spanning pipelines
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 2015
The design of free-spanning pipelines is performed with the aim of ensuring their integrity against permanent loads generated by seabed roughness, functional loads induced by internal pressure and temperature, and dynamic loads induced by marine currents and direct wave action. In particular, a load and resistance factored design is applied that focuses on extreme environmental loads, and a fatigue limit state approach is applied as a consequence of free-span dynamics due to vortex shedding-induced vibration and direct wave action. The pipeline free-span scenario can be permanent, when generated by seabed roughness, or characterized by short- to long-term evolution, when generated by seabed mobility and scouring in shallow waters. Free-span analysis is generally a task involving a number of disciplines and should be carried out using a multidisciplinary approach. The paper illustrates various themes related to free-span analysis: (i) free-span scenarios, (ii) characterization of the...
Vortex-Induced Vibration of Steel Catenary Riser Under Vessel Motion
Volume 2: CFD and VIV, 2014
A truncated steel catenary riser (SCR) model was experimentally tested in the ocean basin by oscillating the top end of the model to simulate the heave and surge vessel motion in order to investigate the vortex-induced vibration (VIV) features. Out-of-plane VIV responses were generally analyzed revealing that although the root mean square (RMS) strain distributed rather broadband, the displacement was quite consistent within a narrowband from 0.2D to 0.3D, and the touch-down point (TDP) area was found not to be the place suffering the maximum out-of-plane VIV response due to near wall effects. What's more, strong wave propagations were firstly reported and summarized as a distinguished feature for VIV of a SCR under vessel motions, and further results reveal that wave propagation during the 'lift up' phase was quite different from that during 'push down' in terms of both wave speed and 'power-in' region location which is assumed to be caused by the tension variation along the model.