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The dynamic interaction between pipeline vibration and local scour is investigated numerically. The sediment scour model is adopted to calculate the local scour below pipeline. The general moving objects (GMO) model fully coupled with the fluids is established to simulate the pipeline vibration. The present results are consistent with the previous experimental results and show good agreement. The scour depth and scour hole scale are closely related to the amplitude of pipeline vibration. The effects of initial gap-to-diameter ratio, reduced velocity, and pipeline diameter on the local scour and pipeline vibration are investigated. [ABSTRACT FROM AUTHOR]

Vortex-Induced Vibration (VIV) for flexible cylinders is a typical fluid–structure interaction problem, and it becomes more complex when the time-varying axial tension effect is considered. An available force–decomposition model is proposed in this paper to investigate the cross-flow VIV response characteristics with time-varying tension. VIV hydrodynamic forces are all based on forced vibration experimental data, and structural stiffness will be updated at each time step to take the tension variation into account. Firstly, this VIV model is compared against the published experimental results of a small-scale cylinder with constant and time-varying tensions. Next, 60 cases of a long flexible cylinder are designed to investigate the time-varying tension effect comprehensively. Several new phenomena such as amplitude modulation, time-lag, frequency transition, mode jump and multi-frequencies response superposition are captured in the response comparison with the constant tension case. The effects of initial phase, amplitude and frequency of the varying tension are respectively discussed in detail. The Mathieu-type resonance between VIV and time-varying tension excitation is proved existent. The response displacement and strain will enlarge significantly at ω T = 2 ω C T , to which enough attention needs to be paid. [ABSTRACT FROM AUTHOR]

The sharp interface immersed boundary method is assessed for suitability and accuracy in simulating flow-induced vibration, specifically the phenomenon of vortex-induced vibration (VIV) in the two-dimensional flow past an elastically-mounted cylinder. Inherent to immersed boundary methods are the spurious force oscillations observed when the immersed boundary moves across the underlying grid. This deficiency in immersed boundary methods is acute in flows featuring fully-coupled fluid–structure interaction, where these oscillations are fed directly back into the coupled system and have the potential to significantly affect the solution. Here, the immersed boundary method is tested and compared directly and in detail to an accurate and validated spectral-element method. The immersed boundary method performs well for the given problem, excepting a few cases, such as those featuring disordered vortex-shedding. A heuristic model is developed to analyze the frequency content of the observed spurious force oscillations and their potential to affect the global solution. A guide to the resolution required for spatial accuracy is proposed, that around 40 points should span the peak-to-peak distance of any significant oscillation. [ABSTRACT FROM AUTHOR]

This paper investigates the phase angles of the vibrations and hydrodynamic forces by the model testing of a flexible riser's vortex-induced vibration (VIV) under uniform flow. The VIV displacement of the riser is derived from the measured strains in the cross-flow (CF) and inline (IL) directions. Then, the hydrodynamic forces are obtained by the dynamic equation of an Euler-Bernoulli beam based on the results of VIV displacement. The characteristics of the phase angle of displacement and the hydrodynamic forces are analyzed. The results show that the phase angles of displacement and the hydrodynamic forces are almost identical at different cross sections of the riser under uniform flow. Moreover, within two adjacent vibration nodes in IL direction, the phase angle almost kept constant, while had a 180 deg change at the two sides of each vibration node. When the reduced velocity varies from 5.25 to 7.5, the phase angles of displacement derived from the flexible riser's VIV are 45 deg larger than those from the rigid cylinder's self-excited vibration. [ABSTRACT FROM AUTHOR]

We propose a generalized strip modelling method that is computationally efficient for the VIV prediction of long flexible cylinders in three-dimensional incompressible flow. In order to overcome the shortcomings of conventional strip-theory-based 2D models, the fluid domain is divided into “thick” strips, which are sufficiently thick to locally resolve the small scale turbulence effects and three dimensionality of the flow around the cylinder. An attractive feature of the model is that we independently construct a three-dimensional scale resolving model for individual strips, which have local spanwise scale along the cylinder's axial direction and are only coupled through the structural model of the cylinder. Therefore, this approach is able to cover the full spectrum for fully resolved 3D modelling to 2D strip theory. The connection between these strips is achieved through the calculation of a tensioned beam equation, which is used to represent the dynamics of the flexible body. In the limit, however, a single “thick” strip would fill the full 3D domain. A parallel Fourier spectral/ hp element method is employed to solve the 3D flow dynamics in the strip-domain, and then the VIV response prediction is achieved through the strip–structure interactions. Numerical tests on both laminar and turbulent flows as well as the comparison against the fully resolved DNS are presented to demonstrate the applicability of this approach. [ABSTRACT FROM AUTHOR]

The hydrodynamic character of a wall-free and near-wall circular cylinder oscillating in the transverse direction in a steady current was experimentally investigated at a Reynolds number of . Forces in both the in-line and cross-flow directions were measured by three-dimensional force transducers. The effects of the near wall on the hydrodynamic coefficients of the cylinder at high Reynolds number are studied. Experimental results indicate that: (1) the first-order oscillating drag coefficient obtained in the near-wall cases is larger than the second-order oscillating drag coefficient and is almost one-third of the mean drag coefficient; (2) compared with the wall-free cases, the Strouhal number is bigger, and the lock-in phenomenon occurs at a higher nondimensional frequency in the near-wall cases; (3) the near wall has a significant effect on the power transfer and therefore leads to a larger lift coefficient in phase with the velocity than in the wall-free cases, indicating that hydrodynamic coefficients based on wall-free cylinders may not be suitable for predicting the vortex-induced vibration of pipelines; and (4) as the gap ratio decreases to 0.1, the vortex shedding can be totally suppressed by the near wall. [ABSTRACT FROM AUTHOR]

A brief overview of vortex-induced vibration (VIV) of bridge decks is presented, highlighting special VIV features concerning bridge decks. A popular VIV model (Van der Pol-type model) for bridge decks is examined in detail. Alternatively, a truncated Volterra series-based nonlinear oscillator is introduced to model the VIV system. Typical features of VIV such as the limit cycle oscillation (LCO), frequency shift, hysteresis, and beat phenomenon are parsimoniously and accurately captured in the proposed nonlinear model. As a functional expansion of a nonlinear system, the Volterra series is convenient for estimating the linear and nonlinear contributions to VIV. It is demonstrated that the relative contribution of nonlinear effects in VIV is around 50% of the total response for a range of bridge cross sections. The efficacy of the Volterra series as a reduced-order model (ROM) in capturing aerodynamic nonlinearities eliminates the need for reliance on conventional phenomenological models as it promises to offer a unified framework for nonlinear wind effects on long-span bridges-for example, VIV, buffeting, and flutter. [ABSTRACT FROM AUTHOR]

This paper describes an investigation of vortex-induced vibrations in a submerged floating tunnel (SFT) system. A theoretical model for coupled tube-cable vibration was developed to evaluate the SFT structural dynamic response to water current. The differential equations of the cable and tube coupled motion were derived using the Hamilton principle, and approximate numerical analyses were carried out to determine the coupling effect between cable transverse vibrations and tube vertical vibrations. The results showed that the maximum amplitudes of the cables were greater than the initial disturbance when self-induced resonance occurred. Self-induced resonance can be caused by the vortex-induced vibration of the cables when the flow velocity reaches a certain value. The change in the tube-specific gravity ratio had little effect on the maximum vibration amplitudes of the tube and cables. The vibrations of the tube and cables were more sensitive to changes in the lift coefficient than to the added mass coefficient or the drag coefficient. The coupling effect of tube-cable vibration should be weaker with smaller cable angles; after careful consideration, a reasonable choice of angle for the cables was determined to be 45°. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes an experimental investigation into the effect of restricting the vortex-induced vibrations of a spring-mounted rigid cylinder by means of stiff mechanical end-stops. Cases of both asymmetric and symmetric restraint are investigated. Results show that limiting the amplitude of the vibrations strongly affects the dynamics of the cylinder, particularly when the offset is small. Fluid-structure interaction is profoundly affected, and the well-known modes of vortex shedding observed with a linear elastic system are modified or absent. There is no evidence of lock-in, and the dominant impact frequency corresponds to a constant Strouhal number of 0.18. The presence of an end-stop on one side of the motion can lead to large increases in displacements in the opposite direction. Attention is also given to the nature of the developing chaotic motion, and to impact velocities, which in single-sided impacts approach the maximum velocity of a cylinder with linear compliance undergoing VIV at lock-in. With symmetrical end-stops, impact velocities were about one-half of this. Lift coefficients are computed from an analysis of the cylinder motion between impacts. [Copyright &y& Elsevier]

Abstract: Vortex-induced vibration (VIV) tests on full-scale cylinders are undertaken to study the vibration performance of steel tubes connected with typical joints in transmission towers, including [-shaped gusset plate connection, U-shaped gusset plate connection, cross-gusset connection and the flange. Due to the asymmetric flexural stiffness for the cross section of the [-shaped or U-shaped gusset plate, VIV is only generated about the minor axis. The paper presents the relationship between the slenderness ratio and the occurrence wind speed of VIV about the minor axis. Moreover, it has been shown that VIV can occur not only in laminar flows, but also in turbulent flows, and the amplitude decreases as the turbulence intensity rises. The amplitude is affected by the wind attack angle, and drops as the wind attack angle decreases. It is revealed that for the cylinders connected with [-shaped gusset plates with the slenderness ratio of 100∼200, the value of Strouhal number ranges from 0.20 to 0.21and the reduced velocity from 5.0 to 5.5. [Copyright &y& Elsevier]

Abstract: This paper presents a selective review of recent research on vortex-induced vibrations of isolated circular cylinders and the flow and vibration of circular cylinders in a tandem arrangement; a common thread being that the topics raised are of particular interest to the author. The influence of Reynolds number on the response of isolated cylinders is presented and recent developments using forced vibration are discussed. The response of a cylinder free to respond in the in-line and transverse directions is contrasted with that of a cylinder responding in only one direction. The interference between two circular cylinders is discussed and prominence given to the case of cylinders in a tandem arrangement. The origin of the time–mean lift force on the downstream cylinder is considered together with the cause of the large amplitude transverse vibration experienced by the cylinder above vortex resonance. This wake-induced vibration is shown to be a form of vortex-induced vibration. [Copyright &y& Elsevier]

Abstract: A general low-order fluid–structure interaction model capable of evaluating the multi-mode interactions in vortex-induced vibrations of flexible curved/straight structures is presented. Cross-flow motions due to unsteady lift forces of inclined sagged cables and tensioned beams in uniform currents are investigated. In contrast to a linear equation governing the transverse motion of straight beams or cables typically considered in the literature, coupled horizontal/vertical (axial/transverse) displacements and geometric nonlinearities of curved cable (straight beam) are accounted for. A distributed nonlinear wake oscillator is considered in the approximation of space–time varying hydrodynamics. This semi-empirical fluid force model in general depends on the mass-damping parameter and has further been modified to capture both the effects of varying initial curvatures of the inclined cylinder and the Reynolds number. Numerical simulations are performed in the case of varying flow velocities and parametric results highlight several meaningful aspects of vortex-induced vibrations of long flexible cylinders. These comprise multi-mode lock-in, sharing, switching and interaction features in the space and time domains, the estimated maximum modal and total amplitudes, the resonant nonlinear modes of flexible cylinders and their space–time modifications, and the influence of fluid/structure parameters. A shortcoming of single-mode or linear structural model is underlined. Some quantitative and qualitative comparisons of numerical/experimental results are discussed to demonstrate the validity and required improvement of the proposed modelling and analysis predictions. [ABSTRACT FROM AUTHOR]

Abstract: Vortex-induced vibration (VIV) of long flexible cylindrical structures (e.g. risers, pipelines, tendons, mooring lines) enduring ocean currents is ubiquitous in the offshore industry. Though significant effort has gone into understanding this complicated fluid–structure interaction problem, major challenges remain in modeling and predicting the response of such structures (for example a riser). The work presented in this paper provides a systematic approach to estimate and analyze the vortex-induced motions of a marine riser. A systematic framework is developed, which allows reconstruction of the riser motion from a limited number of sensors placed along its length. A full reconstruction criterion is developed, which classifies when the measurements from the sensors contain all information pertinent to riser VIV response, and when they do not, in which case additional, analytical methods must be employed. Reconstruction methods for both scenarios are developed and applied to experimental data. Finally, a systematic study on the error during the reconstruction is also undertaken. The methods developed in this paper can be applied to: improve understanding of the vortex shedding mechanisms, including the presence of traveling waves and higher-harmonic forces; develop tools for in-situ estimation of fatigue damage on marine risers; and estimate the vortex-induced forces on marine risers. [ABSTRACT FROM AUTHOR]

Abstract: Significant past effort has gone into understanding the complicated flow–structure interaction problem of vortex-induced vibration (VIV) of long flexible cylindrical structures (e.g., risers, mooring lines, tendons, conductors) in the ocean environment. However, major challenges persist with regard to riser VIV modeling and response prediction. The existing prediction schemes are based on a number of hypotheses, experimental facts and data like strip theory, energy balance, correlation length and, most importantly, the use of lift force coefficient databases. Recent advances in observing the VIV motions on experimental risers with high confidence shows that some of these assumptions may not be valid. One important source of the discrepancies between theoretical estimates and experimental observations arise from the use of experimentally obtained lift coefficient databases. These databases were obtained under the laboratory conditions of limited Reynolds number, and under the assumption that the cross-flow motions are not influenced by restraining the in-line motions. In this paper we develop a method to improve the modeling capability of riser VIV by extracting empirical lift coefficient databases from field riser VIV measurements. The existing laboratory-based lift coefficient databases are represented in a flexible parameterized form using a set of carefully chosen parameters. Extraction of the lift coefficient parameters is posed as an optimization problem, where the objective is to minimize the error between the prediction using a theoretical model and the experimental data. Application of the method to data from the Norwegian Deepwater Programme experiments shows that the new optimal databases significantly reduce the error in estimating the riser VIV cross-flow response. [Copyright &y& Elsevier]

Although there are a great many papers dedicated to the problem of a cylinder vibrating transverse to a fluid flow (Y-motion), there are almost no papers studying the more practical case of vortex-induced vibration in two degrees of freedom (XY-motion) where the mass and natural frequencies are precisely the same in both X and Y directions. We have designed the present pendulum apparatus to achieve both of these criteria. Even down to the low mass ratios, where m&ast;=6, it is remarkable that the freedom to oscillate in-line with the flow, affects the transverse vibration surprisingly little. There is, however, a dramatic change in the fluid–structure interactions when mass ratios are reduced below m&ast;=6. A new amplitude response branch with significant streamwise motion appears, in what we call the “super-upper” branch, yielding massive amplitudes of 3 diameters peak-to-peak (A&ast;Y∼1.5). We discover a corresponding periodic vortex wake mode, comprising a triplet of vortices being formed in each half cycle, in what we define as a “2T” mode. The extensive studies of VIV for Y-only body motions, built up over the last 35 years, remain of strong relevance, for m&ast;>6. It is only for “light” bodies, m&ast;<6, that one observes a rather marked departure from previous results. [Copyright &y& Elsevier]