Improved In-Line VIV Prediction for Combined In-Line and Cross-Flow VIV Responses

2017 ◽  
Author(s):  
Decao Yin ◽  
Elizabeth Passano ◽  
Carl M. Larsen
Keyword(s):  
Cross Flow ◽  
Test Results ◽  
Marine Structures ◽  
Flexible Pipe ◽  
Forced Motion ◽  
Pipe Model ◽  
Vortex Induced Vibrations ◽  
Harmonic Components ◽  
Operation Phase ◽  
Semi Empirical

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. VIV prediction tools are based on hydrodynamic coefficients, which are obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or cross-flow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software VIVANA to perform combined IL and CF VIV calculation. The key IL results are compared with NDP flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.

Improved In-Line Vortex-Induced Vibrations Prediction for Combined In-Line and Cross-Flow Vortex-Induced Vibrations Responses

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Decao Yin ◽  
Elizabeth Passano ◽  
Carl M. Larsen
Keyword(s):  
Cross Flow ◽  
Hydrodynamic Coefficients ◽  
Marine Structures ◽  
Flexible Pipe ◽  
Flexible Beams ◽  
Forced Motion ◽  
Pipe Model ◽  
Vortex Induced Vibrations ◽  
Flow Vortex ◽  
Semi Empirical

Slender marine structures are subjected to ocean currents, which can cause vortex-induced vibrations (VIV). Accumulated damage due to VIV can shorten the fatigue life of marine structures, so it needs to be considered in the design and operation phase. Semi-empirical VIV prediction tools are based on hydrodynamic coefficients. The hydrodynamic coefficients can either be calculated from experiments on flexible beams by using inverse analysis or theoretical methods, or obtained from forced motion experiments on a circular cylinder. Most of the forced motion experiments apply harmonic motions in either in-line (IL) or crossflow (CF) direction. Combined IL and CF forced motion experiments are also reported. However, measured motions from flexible pipe VIV tests contain higher order harmonic components, which have not yet been extensively studied. This paper presents results from conventional forced motion VIV experiments, but using measured motions taken from a flexible pipe undergoing VIV. The IL excitation coefficients were used by semi-empirical VIV prediction software vivana to perform combined IL and CF VIV calculation. The key IL results are compared with Norwegian Deepwater Programme (NDP) flexible pipe model test results. By using present IL excitation coefficients, the prediction of IL responses for combined IL and CF VIV responses is improved.

VIV of Free Spanning Pipelines: Comparison of Response From Semi-Empirical Code to Model Tests

2010 ◽  
Author(s):  
Elizabeth Passano ◽  
Carl M. Larsen ◽  
Jie Wu
Keyword(s):  
Cross Flow ◽  
Model Tests ◽  
Test Series ◽  
The Finite Element Method ◽  
Field Development ◽  
Long Span ◽  
Flow Response ◽  
Pipe Model ◽  
Vortex Induced Vibrations ◽  
Semi Empirical

The purpose of this paper is to compare predictions of vortex-induced vibrations (VIV) from a semi-empirical program to experimental data. The data is taken from a VIV model test program of a free span pipeline using a long elastic pipe model. Both in-line (IL) and cross-flow (CF) vibrations are compared. The Norwegian Ormen Lange field development included pipelines laid on very uneven seafloors, resulting in many free spans. As part of the preparations for this field development, VIV model tests of single- and multi-span pipelines were carried out at MARINTEK for Norsk Hydro, which later became a part of Statoil. The VIVANA program is a semi-empirical frequency domain program based on the finite element method. The program was originally developed by MARINTEK and the Norwegian University of Science and Technology (NTNU) to predict cross-flow response due to VIV. The fluid-structure interaction in VIVANA is described using added mass, excitation and damping coefficients. Default curves are available or the user may input other data. VIVANA originally included only cross-flow excitation but pure in-line excitation was later added. Recently, simultaneous cross-flow and in-line excitation has also been included. At present, the excitation in the cross-flow and in-line directions is not coupled. Coefficients for simultaneous cross-flow and in-line excitation have been proposed and are available in VIVANA. In this paper, response predicted by VIVANA has been compared to the Ormen Lange model tests for selected test series. The analyses with pure IL loading gave good estimates of IL response up to and beyond the start of CF response. The analyses with combined CF and IL loading gave good response estimates for the test series with a long span. The experiments with short spans tended to give CF and IL mode 1 response while the present version of the program gave IL response at higher modes. The present coefficient based approach is, however, promising. Further work should aim at establishing better coefficients and to understanding the interaction between CF and IL response.

scholarly journals Kill Line Model Cross Flow Inline Coupled Vortex-Induced Vibration

2017 ◽  
Author(s):  
Baiheng Wu ◽  
Jorlyn Le Garrec ◽  
Dixia Fan ◽  
Michael S. Triantafyllou
Keyword(s):  
Bluff Body ◽  
Oil And Gas ◽  
Cross Flow ◽  
The Body ◽  
Bluff Bodies ◽  
Structural Vibrations ◽  
Vortex Induced Vibrations ◽  
Series Of Experiments ◽  
Central Pipe ◽  
Semi Empirical

Currents and waves cause flow-structure interaction problems in systems installed in the ocean. Particularly for bluff bodies, vortices form in the body wake, which can cause strong structural vibrations (Vortex-Induced Vibrations, VIV). The magnitude and frequency content of VIV is determined by the shape, material properties, and size of the bluff body, and the nature and velocity of the oncoming flow. Riser systems are extensively used in the ocean to drill for oil wells, or produce oil and gas from the bottom of the ocean. Risers often consist of a central pipe, surrounded by several smaller cylinders, including the kill and choke lines. We present a series of experiments involving forced in-line and cross flow motions of short rigid sections of a riser containing 6 symmetrically arranged kill and choke lines. The experiments were carried out at the MIT Towing Tank. We present a systematic database of the hydrodynamic coefficients, consisting of the forces in phase with velocity and the added mass coefficients that are also suitable to be used with semi-empirical VIV predicting codes.

Experimental Investigation of Vortex-Induced Vibration Responses of Tension Riser Transporting Fluid

2009 ◽  
Author(s):  
Yongbo Zhang ◽  
Fanshun Meng ◽  
Haiyan Guo
Keyword(s):  
Experimental Investigation ◽  
Frequency Spectrum ◽  
Cross Flow ◽  
Internal Flow ◽  
Strain Gauges ◽  
Test Results ◽  
Amplitude Response ◽  
Flowing Fluid ◽  
Vortex Induced Vibrations ◽  
Vibration Responses

This paper presents the test results of a vertically tensioned riser model under vortex-induced vibrations. The influence of internal flowing fluid and top tensions on the riser behavior is investigated. Twelve strain gauges were mounted on the riser and both the in-line and cross-flow responses at locations were measured. The frequency spectrum and amplitude response were derived from the strain date. The influences of internal flow and top tensions on two kinds of model risers are analyzed and some conclusions are drawn.

Comparison of Calculated In-Line Vortex Induced Vibrations to Model Tests

2012 ◽  
Author(s):  
Elizabeth Passano ◽  
Carl M. Larsen ◽  
Halvor Lie
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Model Tests ◽  
The Finite Element Method ◽  
Response Frequency ◽  
Flow Response ◽  
Vortex Induced Vibrations ◽  
Flow Directions ◽  
The Cross ◽  
Semi Empirical

The purpose of the present paper is to compare vortex-induced vibrations (VIV) in both in-line and cross-flow directions calculated by a semi-empirical computer program to experimental data. The experiments used are the Bearman and Chaplin experiments in which a model of a tensioned riser is partly exposed to current and partly in still water. The VIVANA program is a semi-empirical frequency domain program based on the finite element method. The program was developed by MARINTEK and the Norwegian University of Science and Technology (NTNU) to predict cross-flow response due to VIV. The fluid-structure interaction in VIVANA is described using added mass, excitation and damping coefficients. Later, curves for excitation, added mass and damping for pure in-line VIV response were added. These curves are valid for low current levels, before the onset of cross-flow VIV response. Recently, calculation of response from simultaneous cross-flow and in-line excitation has been included in VIVANA. The in-line response frequency is fixed at twice the cross-flow response frequency and the in-line added mass is adjusted so that this frequency becomes an eigenfrequency. A set of curves based on forces measured during combined cross-flow and inline motions are used. At present, the in-line excitation curves are not dependent on the cross-flow response amplitude. In the paper, in-line and cross-flow response predicted by VIVANA will be compared to the Bearman and Chaplin model tests. The choice of added mass and excitation coefficients will be discussed.

scholarly journals In-Line VIV Based on Forced-Vibration Tests

2019 ◽  
Author(s):  
Decao Yin ◽  
Jie Wu ◽  
Elizabeth Passano ◽  
Halvor Lie ◽  
Ralf Peek ◽  
...  
Keyword(s):  
Response Function ◽  
Forced Vibration ◽  
Cross Flow ◽  
Companion Paper ◽  
Travelling Wave ◽  
Function Approach ◽  
Flexible Pipe ◽  
Wave Effects ◽  
Vibration Tests ◽  
Semi Empirical

Abstract Excitation and added mass functions determined from forced vibration tests of a rigid cylinder undergoing harmonic motion in the flow are used in the semi-empirical software VIVANA to predict the VIV response of pipelines. An advantage of this approach, as opposed to the more-commonly-used response function approach, is that it can account for changing conditions along the length of the pipe, like changing current velocity, seabed proximity, and/or pipe diameter. This makes it useful for pipelines as well as for risers when such changes occur. Further, for pipelines, travelling wave effects play less of a role than for risers, so the VIVANA approach can be simplified by assuming the phase angle of the harmonic response is constant along the span. The interactions between cross-flow and in-line response that complicate the prediction of cross-flow VIV by the excitation function approach, do not arise for pure inline VIV. For the latter case, using the pure in-line forced vibration test data of Aronsen (2007), it is found that both VIVANA approach and simplified ‘SIVANA’ approach thereof predict VIV amplitudes consistent with experiments on flexible pipe (Ormen Lange umbilical VIV tests), and the DNVGL-RP-F105 response function for a range of structural and soil damping values. In a companion paper, this approach is applied partially strake-covered pipeline spans, to show that a relatively small fraction of well-placed strake coverage is enough to suppress in-line VIV.

scholarly journals VIV Responses of Riser With Buoyancy Elements: Forced Motion Test and Numerical Prediction

2017 ◽  
Author(s):  
Jie Wu ◽  
Halvor Lie ◽  
ShiXiao Fu ◽  
Rolf Baarholm ◽  
Yiannis Constantinides
Keyword(s):  
Numerical Methods ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Good Prediction ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Forced Motion ◽  
Vortex Induced Vibrations ◽  
The Difference ◽  
Hydrodynamic Data

Steel Lazy Wave Riser (SLWR) is an attractive deep water riser concept. When subjected to vortex induced vibrations (VIV), the vortex shedding process of the buoyancy element and the bare riser section will be different due to the difference in diameter. VIV responses can be strongly influenced by the dimension of the buoyancy element and its arrangement. Empirical VIV prediction programs, such as VIVANA, SHEAR7 and VIVA, are widely used by the industry for design against VIV loads. However, there is lack of hydrodynamic data to be used in these programs when buoyancy elements are present. Experiment to obtain hydrodynamic data for riser with staggered buoyancy elements was carried out in the towing tank in SINTEF Ocean. A rigid cylinder section with three staggered buoyancy elements was subjected to harmonic forced cross-flow (CF) motions. Hydrodynamic forces on one of the buoyancy elements were directly measured in addition to the measured forces at both ends of the test section. Two buoyancy element configurations were tested and the corresponding hydrodynamic data are compared with that of a bare cylinder. The obtained hydrodynamic data was also used in VIV prediction software and good prediction against existing flexible cylinder staggered buoyancy element VIV test data was achieved. A roadmap to achieve an optimal SLWR design by combining different experimental and numerical methods is suggested.

Experimental and Numerical Analysis of Forced Motion of a Circular Cylinder

2011 ◽  
Author(s):  
Decao Yin ◽  
Carl M. Larsen
Keyword(s):  
Influence Factor ◽  
Amplitude Ratio ◽  
Cross Flow ◽  
Flexible Beam ◽  
Hydrodynamic Coefficients ◽  
Forced Motion ◽  
Vortex Pattern ◽  
Severe Fatigue ◽  
Vortex Induced Vibrations ◽  
Uniform Current

Vortex induced vibrations (VIV) of long, slender marine structures may cause severe fatigue damage. However, VIV is still not fully understood, which calls for further research on this topic. This paper discusses results from experimental and numerical investigations of forces on rigid cylinders subjected to combined in-line (IL) and cross-flow (CF) motions, and it aims at improving the understanding of the interaction between IL and CF response components. Model tests with a long flexible beam were conducted at MARINTEK for the Norwegian Deepwater Programme (NDP). The model was 38 m long and it was towed horizontally so that both uniform and linear sheared current profiles could be obtained. Orbits for cross section motions at selected positions along the beam were identified in these tests. Forced motion experiments using these orbits were later carried out in the Marine Cybernetic Laboratory at Norwegian University of Science and Technology (NTNU). A 2 m long rigid cylinder was towed horizontally and forced to follow the measured orbits with identical amplitude ratio, non-dimensional frequency and Reynolds number as for the flexible beam tests. Parts of the results from these tests were published by Yin & Larsen in 2010. In this paper results from an investigation of trajectories for six positions along the beam in a uniform current condition will be shown. Three orbits have nearly the same CF amplitude ratio at the primary CF frequency, and the other three have similar IL amplitude ratio at the primary IL frequency, which is twice the CF frequency. Hydrodynamic coefficients have been found from experiments and numerical computations were carried out to find vortex shedding patterns for these cases. The main conclusions are that the IL motion component is a significant influence factor, and that higher order displacement components are more pronounced in IL direction than CF. Significant displacements in IL direction at 6 times the primary CF frequency were also observed, the ‘2T’ vortex pattern was captured when strong IL motion components were present. It is also seen that hydrodynamic coefficients should be found for combined CF and IL orbits and thereby improve the empirical models for prediction of VIV.

Forced Motion Experiments With Measured Motions From Flexible Beam Tests Under Uniform and Sheared Flows

2012 ◽  
Author(s):  
Decao Yin ◽  
Carl M. Larsen
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Amplitude Modulation ◽  
Cross Flow ◽  
Hydrodynamic Forces ◽  
Flexible Beam ◽  
Forced Motion ◽  
Vortex Induced Vibrations ◽  
Time Histories ◽  
Orbit Types

Hydrodynamic forces on a cylinder under realistic combinations of in-line (IL) and cross-flow (CF) vortex induced vibrations (VIV) have been investigated. Signals of strain gauges and accelerometers from the Norwegian Deepwater Programme (NDP) tests with a long, slender beam were used to identify cross section orbits. 19 cross sections almost evenly distributed along the pipe were selected, and their motions were applied in controlled motion experiments with a rigid cylinder. Dimensionless parameters like Reynolds number and non-dimensional frequency were identical for the two sets of experiments. Comparison between hydrodynamic coefficients found from forced motion tests with observed motion time histories and periodic approximations are presented. Force histories are also investigated in detail. Orbit types for combined IL and CF VIV are categorized based on relative amplitude and phase, and it is shown that IL motions exhibit chaotic character more easily than CF. Amplitude modulation is observed frequently. Cases where cross section motions are close to periodic have similar hydrodynamic forces as for periodic motion, implying that periodic forced motion tests are relevant to get valid force information. Many cases have amplitude modulated IL motions, while CF motions are quasi-steady. In such cases, IL amplitude modulation can cause abrupt change of IL forces and also 3rd order CF forces, which can accumulate large fatigue damage. When both IL and CF motions are chaotic, the force-motion relationship is impossible to describe by constant coefficients.

Hydrodynamics of Flexible Pipe With Staggered Buoyancy Elements Undergoing Vortex-Induced Vibrations

2017 ◽  
Author(s):  
Mengmeng Zhang ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Jie Wu ◽  
Halvor Lie ◽  
...  
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Forced Oscillations ◽  
Hydrodynamic Characteristics ◽  
Ocean Engineering ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Vortex Induced Vibrations ◽  
Coefficients Identification ◽  
The Relationship

Flexible riser with staggered buoyancy elements has been widely used in ocean engineering, such as steel lazy wave riser, drilling riser, etc. Both the buoyancy elements and the riser may experience vortex induced vibrations (VIV), subject to sea current. However, hydrodynamic characteristics of the buoyancy elements undergoing VIV and influence of buoyancy elements on hydrodynamic force of the bare section are still under discussion. The purpose of this paper is to reveal the hydrodynamic characteristics of flexible riser with staggered buoyancy elements, both for buoyancy element and bare pipe section. The cross flow hydrodynamic coefficients of the flexible riser with 25%, 50% and 100% staggered buoyancy covered are obtained from VIV model tests, using hydrodynamic forces and coefficients identification method. Distribution of the added mass coefficients and excitation coefficients along the flexible riser were investigated, and compared with those on the bare flexible pipe and rigid cylinders under forced oscillations. In addition, the relationship between added-mass coefficients of buoyancy element and that of bare section were obtained.

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