Cross-Flow Vortex-Induced Vibration Simulation of Flexible Risers Employing Structural Systems of Different Nonlinearities With a Wake Oscillator

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Shuai Meng ◽  
Xuefeng Wang
Keyword(s):  
Structural Model ◽  
Cross Flow ◽  
Linear Structure ◽  
Structural Systems ◽  
Axial Deformation ◽  
Vortex Induced Vibration ◽  
Wake Oscillator ◽  
Structural Nonlinearities ◽  
Flexible Risers ◽  
Vibration Simulation

To achieve a reliable structural model for vortex-induced vibration (VIV) the prediction of flexible risers, this paper employs structural systems with different geometrical nonlinearities (including a linear structure, a nonlinear one, a coupled cross-flow, and axial nonlinear one) and a classical oscillator to simulate cross-flow VIV. By comparing the experimental and simulation results, it is found that when the drag coefficient is assumed to be a fixed constant along the cylinder (i.e., the damping model is linear function of current velocity), it can affect the vibration amplitude considerably and may alter the dominant modes. When the excited mode of VIV is bending-stiffness dominant, the cross-flow structural nonlinearities can have a profound stiffening effect on vibration response. Although the introduction of axial deformation can reduce this function, the coupled cross-flow and axial nonlinearities still have the effect of decreasing the VIV amplitude.

Experimental Investigation of the Effects of the In-Line Top-Motion on the Vortex-Induced Vibration Response of a Flexible Riser

2020 ◽  
Author(s):  
Wei Yang ◽  
Chuanzhen Ma ◽  
Zhuang Kang ◽  
Cheng Zhang ◽  
Shaojie Li
Keyword(s):  
Experimental Investigation ◽  
Vibration Frequency ◽  
Flow Direction ◽  
Excitation Frequency ◽  
Cross Flow ◽  
Excitation Amplitude ◽  
Flexible Cylinder ◽  
Amplitude Analysis ◽  
Vortex Induced Vibration ◽  
Flexible Risers

Abstract In order to understand the relation between top-motion and VIV of flexible risers, this paper presents an experimental investigation on concomitant vortex-induced vibration and top-motion excitation with flexible risers. The riser can was mounted vertically, with the diameter of 2 cm and the length of 5 m. The responses of amplitude, frequency and other parameters were analyzed in detail under conditions of different excitation amplitude and frequency in uniform flow. It was found that the concomitant VIV and top-motion excitation significantly affects the flexible cylinder response when compared to the pure VIV tests. The amplitude analysis results show that when the reduced velocity is small (less than about 15), the top-motion excitation has an important influence on amplitude of in-line directions. However, the excitation amplitude and frequency of in-line direction have a little influence on amplitude of cross flow direction. The frequency analysis results show that when the reduced velocity is small (less than about 5), the riser motion amplitude is small and irregular in different excitation and when the reduced velocity is large (5 < Ur < 55), the in-line vibration frequency is two times the cross-flow vibration frequency. A strong connection between the top-motion excitation frequency and the vibration frequency was also found. Overall, some phenomena and characteristics observed in the VIV considering top-motion excitation are different from those in classic VIV, which may provide basic reference for the VIV investigation involving the effect of floating bodies.

Passive Suppression Mechanisms in Laminar Vortex-Induced Vibration of a Sprung Cylinder With a Strongly Nonlinear, Dissipative Oscillator

2017 ◽  
Vol 84 (8) ◽  
Author(s):  
Antoine Blanchard ◽  
Lawrence A. Bergman ◽  
Alexander F. Vakakis
Keyword(s):  
Parameter Space ◽  
Stokes Equations ◽  
Density Ratio ◽  
Cross Flow ◽  
Nonlinear Energy Sink ◽  
Spectral Element ◽  
Body Motion ◽  
Vortex Induced Vibration ◽  
Wake Oscillator ◽  
Viv Suppression

We study cross-flow vortex-induced vibration (VIV) of a linearly sprung circular cylinder equipped with a dissipative oscillator with cubic stiffness nonlinearity, restrained to move in the direction of travel of the cylinder. The dissipative, essentially nonlinear coupling between the cylinder and the oscillator allows for targeted energy transfer (TET) from the former to the latter, whereby the oscillator acts as a nonlinear energy sink (NES) capable of passively suppressing cylinder oscillations. For fixed values of the Reynolds number (Re = 48, slightly above the fixed-cylinder Hopf bifurcation), cylinder-to-fluid density ratio, and dimensionless cylinder spring constant, spectral-element simulations of the Navier–Stokes equations coupled to the rigid-body motion show that different combinations of NES parameters lead to different long-time attractors of the dynamics. We identify four such attractors which do not coexist at any given point in the parameter space, three of which lead to at least partial VIV suppression. We construct a reduced-order model (ROM) of the fluid–structure interaction (FSI) based on a wake oscillator to analytically study those four mechanisms seen in the high-fidelity simulations and determine their respective regions of existence in the parameter space. Asymptotic analysis of the ROM relies on complexification-averaging (CX-A) and slow–fast partition of the transient dynamics and predicts the existence of complete and partial VIV-suppression mechanisms, relaxation cycles, and Hopf and Shilnikov bifurcations. These outcomes are confirmed by numerical integration of the ROM and comparisons with spectral-element simulations of the full system.

scholarly journals Prediction of Vortex-Induced Vibration Response of Deep Sea Top-Tensioned Riser in Sheared Flow Considering Parametric Excitations

2020 ◽  
Vol 27 (2) ◽  
pp. 48-57
Author(s):  
Guanghai Gao ◽  
Yunjing Cui ◽  
Xingqi Qiu
Keyword(s):  
Prediction Model ◽  
Deep Sea ◽  
Nonlinear Partial Differential Equations ◽  
Solution Process ◽  
Cross Flow ◽  
Vortex Induced Vibration ◽  
Sheared Flow ◽  
Wake Oscillator ◽  
Real Size ◽  
Heave Motion

AbstractIt is widely accepted that vortex-induced vibration (VIV) is a major concern in the design of deep sea top-tensioned risers, especially when the riser is subjected to axial parametric excitations. An improved time domain prediction model was proposed in this paper. The prediction model was based on classical van der Pol wake oscillator models, and the impacts of the riser in-line vibration and vessel heave motion were considered. The finite element, Newmark-β and Newton‒Raphson methods were adopted to solve the coupled nonlinear partial differential equations. The entire numerical solution process was realised by a self-developed program based on MATLAB. Comparisons between the numerical calculation and the published experimental test were conducted in this paper. The in-line and cross-flow VIV responses of a real size top-tensioned riser in linear sheared flow were analysed. The effects of the vessel heave amplitude and frequency on the riser VIV were also studied. The results show that the vibration displacements of the riser are larger than the case without vessel heave motion. The vibration modes and frequencies of the riser are also changed due to the vessel heave motion

Dynamic Response of a Fluid-Conveying Riser Subject to Vortex-Induced Vibration: Integral Transform Solution

2014 ◽  
Author(s):  
Jijun Gu ◽  
Zhenhua Song ◽  
Kang Zhang ◽  
Liguo Su ◽  
Menglan Duan
Keyword(s):  
Differential Equations ◽  
Dynamic Response ◽  
Integral Transform ◽  
Fluid Velocity ◽  
Critical Evaluation ◽  
Cross Flow ◽  
Coupled System ◽  
Vortex Induced Vibration ◽  
Wake Oscillator ◽  
Line Force

Analysis of dynamic response of a fluid-conveying riser is an important aspect in subsea production system. In the present paper, dynamic response of a pinned-pinned riser subject to external fluid force was solved by the generalized integral transform technique (GITT). A nonlinear wake oscillator models was used to represent the cross-flow and in-line force acting on the riser, leading to a coupled system of second-order Partial Differential Equations (PDEs). The GITT approach was used to transform the system of PDEs to a system of Ordinary Differential Equations (ODEs), which was numerically solved by using the Adams-Moulton and Gear method (DIVPAG) developed by the International Mathematics and Statistics Library (IMSL). Numerical results were presented for comparison to those given by the numerical and experimental results, allowing a critical evaluation of the technique performance. The influence of conveying fluid velocity and mean top tension were evaluated to show that they should not be negligible in numerical simulation of Vortex-Induced Vibration of a long flexible riser.

A Phenomenological Model for Vortex-Induced Motions of the Monocolumn Platform and Comparison With Experiments

2009 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Rodolfo T. Gonc¸alves ◽  
Andre´ L. C. Fujarra ◽  
Kazuo Nishimoto ◽  
Marcos D. Ferreira
Keyword(s):  
Time Domain ◽  
Phenomenological Model ◽  
Structural Model ◽  
Design Phase ◽  
Van Der Pol ◽  
Floating Structures ◽  
Towing Tank ◽  
Wake Oscillator ◽  
Two Degree Of Freedom ◽  
Comparison With Experiments

Vortex-Induced Motions (VIM) of floating structures is a very relevant subject for the design of mooring and riser systems. In the design phase, Spar VIM behavior as well as Semi Submersible and Tension Leg Platform (TLP) flow-induced motions are studied and evaluated. This paper discusses flow-induced behavior on the Monocolumn concept by presenting a phenomenological model and comparing its results with a set of experiments that took place in the IPT Towing Tank - Brazil (September 2008). The experimental results have shown some fundamental differences from previous VIM tests on other units such as Spars. This numerical model attempts to identify these disparities in order to better understand the mechanics of this phenomenon. The model is based on a time-domain, two degree-of-freedom structural model coupled with a van der Pol type wake oscillator. The comparison was performed in order to calibrate the model, to study and better understand the tests results, and finally to identify important aspects to investigate in further experiments.

The Study on the Influence of Pipe-Soil Interaction on VIV for Different Free Span Types

2017 ◽  
Author(s):  
Chongyao Zhou ◽  
Gang Xu ◽  
Zhiming Huang ◽  
Dagang Zhang ◽  
Naiquan Ye ◽  
...  
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Sensitivity Study ◽  
Structural Damping ◽  
Flexible Pipe ◽  
Wake Oscillator Model ◽  
Wake Oscillator ◽  
Different Types ◽  
Main Factors ◽  
Parameter Influence

Subsea pipeline laid on the seabed will experience free span when the lay path is long and seabed is rugged. Hydrodynamic loads caused by the currents around the pipeline can induce oscillations in both cross-flow and in-line directions. This phenomenon is called vortex-induced vibration (VIV) which is the most common case that could induce serious fatigue problems. The pipe-soil interaction is one of the main factors that influence the vibration. In this paper, a study focusing on the effect of pipe-soil interaction on VIV for different types of free span is presented. The Milan wake oscillator is applied to calculate the dynamic response induced by VIV in Orcaflex, and the results are compared with experimental data to identify its validity. A sensitivity study is also performed to study the parameter influence of the Milan wake oscillator model. Four types of free span (including the multiple free spans) are modeled in Orcaflex and time domain VIV analysis is carried out to study the influence of pipe-soil interaction. Comparison among different types of free span is discussed. The influence of structural damping is studied for flexible pipe only because its influence on steel pipe is negligible. The influence of structural damping on flexible pipe is studied by means of a predefined moment-curvature curve. In addition, several cases are studied to investigate the influence of tension on VIV by Milan wake oscillator.

A Double Birkhoff Wake Oscillator for the Modeling of Vortex-Induced Vibration

2011 ◽  
Author(s):  
R. H. M. Ogink
Keyword(s):  
Free Vibration ◽  
Added Mass ◽  
Mass Force ◽  
Near Wake ◽  
Vibration Measurements ◽  
Vortex Induced Vibration ◽  
Fluid Forces ◽  
Wake Oscillator ◽  
Model Equations ◽  
Far Wake

A double Birkhoff wake oscillator for the modeling of vortex-induced vibration is presented in which the oscillating variables are assumed to be associated with the boundary layer/near wake and the far wake. The fluid forces are assumed to consist of a potential added mass force and a force due to vortex shedding. In the limit of vanishing incoming flow velocity, the model equations reduce to a form similar to the Morison equation. The results of the double wake oscillator have been compared with forced vibration measurements and free vibration measurements over a range of mass and damping ratios. The model is capable of describing the most important trends in both the forced and free vibration experiments. Specifically, the double wake oscillator is able to model both the upper and lower branch of free vibration.

scholarly journals Numerical and Experimental Research on the Effect of Platform Heave Motion on Vortex-Induced Vibration of Deep Sea Top-Tensioned Riser

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Jie Zhang ◽  
Ying Zeng ◽  
Yougang Tang ◽  
Wenyun Guo ◽  
Zhenkui Wang
Keyword(s):  
Parametric Excitation ◽  
Deep Sea ◽  
Frequency Component ◽  
Vortex Induced Vibration ◽  
Wake Oscillator ◽  
Validation Experiment ◽  
Simulation And Experiment ◽  
Prediction And Control ◽  
Heave Motion ◽  
And Control

The prediction and control of vortex-induced vibration (VIV) is one of the key problems for riser design. The effect of platform heave motion on VIV of deep sea top-tensioned riser (TTR) is presented by means of numerical simulation and experiment in this research. First, the heave motion was modeled as a parametric excitation, and the governing equation of VIV of riser considering the parametric excitation was established. Then, the dynamic response of TTR was calculated numerically by the finite difference method based on the Van der Pol wake-oscillator model. Finally, a validation experiment was carried out at the towing tank of Tianjin university. The results show that the VIV response at the bottom of riser is significantly increased due to the platform heave motion, especially in the situation of low current velocity. The larger amplitude and the higher frequency of the platform heave motion with the greater influence are generated on VIV of TTR. In particular, the value of 0.5 times, 1 time, or other multiples of the platform heave frequency will be included in the vibration frequency component of TTR when the platform heave amplitude is large and the frequency is high.

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