Simulation Of Vortex-induced Vibration Research Articles

Numerical Study of Vortex-Excited Vibration of Flexible Cylindrical Structures with Surface Bulge

This study conducted numerical simulations of three-dimensional vortex-induced vibrations (VIV) on cylindrical bodies with various surface protrusion coverage rates, systematically investigating the impact of coverage and protrusion height on the vibrational response of flexible cylinders. The fluid forces on the surface of the riser were resolved using the finite volume method, while the structural forces were solved with the finite element method. A strongly coupled approach was employed for iterative updates between the flow field and structural field data, achieving a bidirectional flow–structure coupling simulation of VIV in a marine environment. The study further explored the performance of surface protrusions in suppressing VIV and considered protrusion heights of 0.1 times the cylinder diameter (0.1D) under coverage rates (CR) of 0%, 10%, 20%, 30%, and 40%, as well as seven different protrusion heights of 0.05D, 0.1D, and 0.15D at a 20% coverage rate. The mechanism of VIV suppression by surface protrusions was identified as altering the separation point of the shear layer and the frequency of vortex shedding through the vortices formed between the surface protrusions. It was found that a 20% coverage rate with a protrusion height of 0.01D (CR20) effectively suppressed the VIV of the cylinder, showing the best performance in VIV suppression, with an efficiency of 30.04%. These results provide a theoretical basis for designing more efficient VIV suppression devices and contribute to enhancing the resistance of marine structures against vortex-induced vibrations.

Reproducing vortex-induced vibrations of rooftop twin-mast by multi-scale coupled simulation of urban wind fields

The Shenzhen Electronics Group (SEG) Plaza in Shenzhen, China, experienced visible vibrations attributed to significant vortex-induced vibrations of the large spacing twin-mast atop the building. The vibration event occurred under complex urban wind environments. In order to reproduce wind fields around SEG Plaza, a multiscale simulation was carried out by integrating the Weather Research and Forecasting (WRF) and Computational Fluid Dynamics (CFD) models. The aerodynamic characteristics and wake modes of twin-mast are investigated by a downscale CFD simulation in detail. Finally, vortex-induced vibration (VIV) of twin-mast was analyzed considering fluid-structure interaction. This work reveals that wind conditions during the SEG Plaza vibration incident were appropriate for the VIV occurrence of twin-mast, and the results of VIV simulation agree well with the field monitoring results by computer vision identification. This study effectively reproduces the full pictures of VIVs of the rooftop twin-mast during this rare event, offering a critical view for the analysis of this event.

A Data-Driven Approach for Generating Vortex-Shedding Regime Maps for an Oscillating Cylinder

This study presents a data-driven approach for generating vortex-shedding maps, which are vital for predicting flow structures in vortex-induced vibration (VIV) wind energy extraction devices, while addressing the computational and complexity limitations of traditional methods. The approach employs unsupervised clustering techniques on subsequences extracted using the matrix profile method from local flow measurements in the wake of an oscillating circular cylinder generated from 2-dimensional computational fluid dynamics simulations of VIV. The proposed clustering methods were validated by reproducing a benchmark map produced at a low Reynolds number (Re = 4000) and then extended to a higher Reynolds number (Re = 10,000) to gain insights into the complex flow regimes. The multi-step clustering methods used density-based and k-Means clustering for the pre-clustering stage and agglomerative clustering using dynamic time warping (DTW) as the similarity measure for final clustering. The clustering methods achieved exceptional performance at high-Reynolds-number flow, with scores in the silhouette index (0.4822 and 0.4694) and Dunn index (0.3156 and 0.2858) demonstrating the accuracy and versatility of the hybrid clustering methods. This data-driven approach enables the generation of more accurate and feasible maps for vortex-shedding applications, which could improve the design and optimization of VIV wind energy harvesting systems.

Effect of grid size and initial conditions on vortex-induced vibration of a circular cylinder

A direct-forcing immersed boundary (DFIB) method was used with an in-house parallelized C++ code to simulate the vortex-induced vibration (VIV) of a one-degree-of-freedom (1-DOF) elastically mounted circular cylinder in the laminar and turbulent flow regimes. The continuity and Navier–Stokes equations were solved numerically together with the equation of motion to study the VIV response of the cylinder in 3-D. The results were analysed and compared with published literature. The importance of conducting a grid independence study at multiple points inside the lock-in (synchronization) region for VIV simulations has been ascertained through detailed comparisons of coarser and finer grids in each of the flow regimes. In addition, for laminar flows, the effect of the grid on the evolution of the vibration response in the lock-in region was discussed. For turbulent flows, the effect of different initial conditions on VIV amplitude was studied, and a hysteresis phenomenon was observed in the initial and upper branches of the lock-in region. The need for multiple calculation methods of vibration amplitudes in turbulent flows was highlighted.

Numerical Simulation of Vortex-Induced Vibration of TTR and SCR

Top tensioned risers (TTRs) and steel catenary risers (SCRs) have been widely used in the field of marine engineering. They are commonly used to transport fluids from subsea wells to surface platforms. Under the action of ocean currents, these risers are often subjected to vortex-induced vibrations (VIVs), which might lead to serious fatigue damage. In this study, VIV around TTR and SCR were numerically simulated using the computational fluid dynamics software FLUENT when the Reynolds number was 4000. In the calculations, the full hexahedron grid and large eddy simulation were used to ensure calculation accuracy from the boundary conditions, as well as solution control. The shape, frequency, and amplitude of VIV produced by TTRs and SCRs at different times and depths were simulated.

Numerical simulation of Vortex-Induced Vibration with bistable springs: Consistency with the Equilibrium Constraint

We present results from two-dimensional numerical simulations based on Immersed Boundary Method (IBM) of a cylinder in uniform fluid flow attached to bistable springs undergoing Vortex-Induced Vibrations (VIV). The elastic spring potential for the bistable springs, consisting of two potential wells, is completely defined by the spacing between the potential minima and the depth of the potential wells. We perform simulations of VIV with linear spring, as well as bistable springs with two different inter-well separations, over a wide range of reduced velocity. As expected, large oscillation amplitudes correspond to lock-in of the lift force with the natural frequency of the spring–mass system. The range of reduced velocity over which lock-in occurs is significantly higher for VIV with bistable springs compared to VIV with linear springs, although the maximum possible amplitude appears to be independent of the spring type. For VIV with bistable springs, the cylinder undergoes double-well oscillations in the lock-in regime. Range of reduced velocity over which lock-in occurs increases when the inter-well distance is reduced. The vortex shedding patterns and amplitude trends look similar at the same equivalent reduced velocity for the different springs. The results here are consistent with our prior theory, in which we propose a new “Equilibrium-Constraint (EC)” based on average kinetic energy budget of the structure. For a given spring potential, the intersection of natural frequency curves with the EC curve yields the possible range of reduced velocities over which lock-in should occur. Our numerical simulations show a collapse of the amplitude-versus-structure frequency data for all the simulations onto roughly the same curve, thus supporting the existence of the EC, and providing an explanation for the trends in the VIV oscillations. The present study provides fundamental insights into VIV characteristics of bistable springs, which may be useful for designing broadband energy harvesters.

Verification of DES for flow over rigidly and elastically-mounted circular cylinders in normal and yawed flow

A computational approach based on a k-ω delayed detached eddy simulation model for predicting aerodynamic loads on a smooth circular cylinder is verified against experiments. Comparisons with experiments are performed for flow over a rigidly-mounted (static) cylinder and for an elastically-mounted rigid cylinder oscillating in the transverse direction due to vortex-induced vibration (VIV). For the static cases, measurement data from the literature is used to validate the predictions for normally-incident flow. New experiments are conducted as a part of this study for yawed flow, where the cylinder axis is inclined with respect to the inflow velocity at the desired yaw angle, β=30∘. Good agreement is observed between the predictions and measurements for mean and rms surface pressure. Three yawed flow cases (β=15∘,30∘,&45∘) are simulated and the results are found to be independent of β (independence principle) when the flow speed normal to the cylinder axis is selected as the reference velocity scale.Dynamic (VIV) simulations for an elastically-mounted rigid cylinder are performed by coupling the flow solver with a solid dynamics solver where the cylinder motion is modeled as a mass–spring–damper system. The simulations accurately predict the displacement amplitude and unsteady loading over a wide range of reduced velocity, including the region where “lock-in” (synchronization) occurs. VIV simulations are performed at two yaw angles, β=0∘ and 45° and the independence principle is found to be valid over the range of reduced velocities tested with a slightly higher discrepancy when the vortex shedding frequency is close to the natural frequency of the system.

Numerical simulation in time domain to study cross-flow VIV of catenary riser subject to vessel motion-induced oscillatory current

The present study proposes a time domain model for the Vortex-induced Vibration (VIV) simulation of a catenary riser under the combination of the current and oscillatory flow induced by vessel motion. In this model, the hydrodynamic force of VIV comprises excitation force, hydrodynamic damping and added mass, which are taken as functions of the non-dimensional frequency and amplitude ratio. The non-dimensional frequency is related with the response frequency, natural frequency, lock-in range and the fluid velocity. The relatively oscillatory flow induced by vessel motion is taken into account in the fluid velocity. Considering that the added mass coefficient and the non-dimensional frequency can affect each other, an iterative analysis is conducted at each time step to update the added mass coefficient and the natural frequency. This model is in detail validated against the published test models. The results show that the model can reasonably reflect the effect of the added mass coefficient on the VIV, and can well predict the riser’s VIV under stationary and oscillatory flow induced by vessel motion. Based on the model, this study carries out the VIV simulation of a catenary riser with harmonic vessel motion. By analyzing the bending moment near the touchdown point, it is found that under the combination of the ocean current and oscillatory flow the vessel motion may decrease the VIV response, while increase the excited frequencies. In addition, the decreasing rate of the VIV under vessel surge is larger than that under vessel heave at small vessel motion velocity, while the situation becomes opposite at large vessel motion velocity.

Discovering time-varying aerodynamics of a prototype bridge by sparse identification of nonlinear dynamical systems.

Vortex-induced vibrations (VIVs) have been observed on a long-span suspension bridge. The nonstationary wind in the field characterized by the time-varying mean wind speed is likely to lead to time-varying aerodynamics of the wind-bridge system during VIVs, which is different from VIVs induced by stationary or even steady wind in wind tunnels. In this paper, data-driven methods are proposed to reveal the time-varying aerodynamics of the wind-bridge system during VIV events based on field measurements on a long-span suspension bridge. First, a variant of the sparse identification of nonlinear dynamics algorithm is proposed to identify parsimonious, time-varying aerodynamical systems that capture VIV events of the bridge. Thus we are able to posit new, data-driven, and interpretable models highlighting the aeroelastic interactions between the wind and bridge. Second, a density-based clustering algorithm is applied to discovering the potential modes of dynamics during VIV events. As a result, the time-dependent model is obtained to reveal the evolution of the aerodynamics of the wind-bridge system over time during an entire VIV event. It is found that the level of self-excited effects of the wind-bridge system is significantly time varying with the real-time wind speed and bridge motion state. The simulations of VIVs by the obtained time-dependent models show high accuracies of the models with an averaged normalized mean-square error of 0.0023. The clustering of obtained models shows underlying distinct dynamical regimes of the wind-bridge system, which are distinguished by the level of self-excited effects.

Numerical simulation of vortex-induced vibration of long flexible risers using a SDVM-FEM coupled method

This paper presents a grid-independent numerical methodology that couples the strip theory based discrete vortex method (SDVM) with the finite element method (FEM) to simulate the vortex-induced vibration (VIV) of a long flexible vertical riser. Based on the strip theory, a three-dimensional flow filed is approximately simulated by a series of computational ‘flow strips’. A Lagrangian discrete vortex method is employed to numerically solve the unsteady vorticity transport equations of each ‘flow strip’. The flexible riser is modelled as a tensioned Bernoulli-Euler beam with the dynamical equation solved by the finite element method in time domain. The two-dimensional DVM code is firstly validated for the VIV simulation of a rigid cylinder that was experimentally studied by Khalak and Williamson (1996). Referring to two typical experimental configurations of Lehn (2003) and Chaplin et al. (2005), the VIV of a long flexible riser immersed in a uniform and stepped incoming flow are numerically simulated, respectively. A good agreement was achieved through detailed comparisons between the present numerical prediction and the experimental data, including the structural in-line and cross-flow VIV response modes, root mean square amplitudes and the dominant frequency. The occurrence of standing and travelling wave responses, dual resonance between in-line and cross-flow motions and figure-eight trajectory are reported. The wake patterns corresponding to two response waves are also presented and investigated. Related to structural local vibration amplitude, two principle vortex patterns resembling the ‘2S’ and ‘2P’ modes are identified in the wake. The standing wave component of structural response determines the vortex shedding pattern. The travelling wave component affects the spanwise vortices shedding at different phases.

Simulation of Vortex-Induced Vibration of Long-Span Bridges: A Nonlinear Normal Mode Approach

Due to the lack of analytic technique for simulating the vortex-induced vibration (VIV) of long-span bridges, a combination of the VIV semi-empirical model with the structural equation of motion is widely employed to calculate the responses of bridge structures. However, the applicability of this method has seldom been investigated before. In this study, the theoretical defects of the conventional combination strategy (i.e. the finite element procedure or the linear normal mode procedure, LNM) are first discussed, a more theoretically reliable approach (the nonlinear norm mode approach, NNM) is then proposed, and the closed-form expression for the NNM of the VIV system is derived. The accuracy of the proposed method is further illustrated by two case studies. This new approach offers a theoretically reliable tool for analyzing the VIV of long-span bridges. It can also be applied to the process of VIV fatigue analysis or control strategy optimization.

Time domain simulation of riser VIV in current and irregular waves

A semi-empirical prediction tool for time domain analysis of cross-flow and in-line vortex-induced vibrations (VIV) is proposed. The model combines concepts from previous publications in a new way, which allows for time domain simulation of VIV together with response phenomena from Morison's equation. To test the prediction tool, a vertical riser exposed to two different flow profiles was modelled, and response predictions were compared to experimental data. The first flow case was steady uniform current, and the second case included irregular waves and current combined. The same empirical coefficients were used to simulate both experiments. In uniform flow, the results were good, although some discrepancies were seen. For the second flow case, the model provided a highly realistic representation of the riser motion. Both when the total response (containing wave and VIV frequencies) and the filtered signal (including only VIV frequencies) were analysed, the predictions followed the measurements closely. Different approaches were subsequently used to find maximum fatigue damage for the riser exposed to current and waves. The industry approach, finding the total damage from independent calculations of wave motion and VIV in uniform current, was compared to the damage produced from the combined analysis. Moderate differences in results between the two strategies were observed. Lastly, the experimental data was analysed to compare riser VIV for the two flow conditions.

CFD Simulation of Vortex Induced Vibration for FRP Composite Riser with Different Modeling Methods

Steel risers are widely used in offshore oil and gas industry. However, the production capacity and depths are limited due to their extreme weight and poor fatigue and corrosion resistance. Nowadays, it is confirmed that fiber reinforced polymer (FRP) composite risers have apparent advantages over steel risers. However, the study of vortex induced vibration (VIV) for composite risers is rarely involved. Three different risers (one steel riser and two composite risers) were compared for their VIV characteristics. The effects of 2D and 3D models and fluid–structure interaction (FSI) were considered. The models of composite risers are established by effective modulus method (EMM) and layered-structure method (LSM). It is found that 2D model are only suitable for ideal condition, while, for real situation, 3D model with FSI has to be considered. The results show that the displacements of the FRP composite risers are significantly larger than those of the steel riser, while the stresses are reversed. In addition, the distributions of the displacements and stresses depend on the geometries, material properties, top-tension force, constraints, etc. In addition, it is obvious that EMM are suitable to study the global working condition while LSM can be utilized to obtain the results in every single composite layer.

Suppression of vortex-induced vibration of a square cylinder via continuous twisting at moderate Reynolds numbers

Vortex-induced vibration (VIV) of elastic structures with a square-shaped prismatic column exposed to flow has a significant impact on many aspects of structural design and stability. The main aim of the present numerical study is to investigate an alternative design of square column for minimizing the impact of VIV on the elastic structures. The numerical study is carried out at moderate Reynolds numbers (1000 ≤ Re ≤ 22000). For both stationary and freely vibrating square cylinders, a systematic validation of the numerical results is performed with the available experimental data. In particular, various turbulence models are explored to assess their effectiveness to capture the separated wake flow dynamics behind the square cylinder. The simulation results via k−ω SST-SAS (Scale Adaptive Simulation) model are found closer to the reported measurements for both stationary and vibrating cases. After establishing the validity of our numerical methodology, the VIV simulations of twisted square cylinders with different twisted angles are performed at the moderate Reynolds numbers. In comparison to the square cylinder counterpart, the results of the twisted square cylinder demonstrate good controlling effect on the VIV response at two oncoming flow directions (0° and 45°). The twisted surface of the cylinder causes the variation of separation or vortex shedding points as well as the frequency of vortex shedding, which in turn affect the distributions of hydrodynamic forces along the cylinder. The power spectral analysis of hydrodynamic forces of twisted square cylinder indicates that the twisted surface has a significant influence on the frequencies of both drag and lift forces. Finally, comparisons of the detailed flow patterns, the 3D vortex structures and the vortex-shedding modes between square and twisted cylinders are presented in detail.

Numerical simulation of VIV for a circular cylinder with a downstream control rod at low Reynolds number

A numerical simulation of the vortex-induced vibration (VIV) at Reynolds number of 500 is carried out for a circular cylinder with a downstream rigidly connected control rod. The mass ratio (m*) and damping ratio (ξ) are fixed as 10 and 5×10−4. The fluid dynamics is obtained by solving arbitrary Lagrangian–Eulerian (ALE) Navier–Stokes equations, and the structure dynamics is solved using Newmark-β method. The grid convergence is tested using five different grids to select the proper mesh. The model and computational method are validated by comparing with the previous research, and a good agreement is reached. The VIV of the cylinder system at eight different gap ratios (G∕D=0.01∼2) are simulated. The responses of the cylinder system are discussed following the classification of the flow patterns at different gap ratios. The same VIV characteristic can be observed in the same flow pattern. The sub-harmonic resonance is observed in the VIV of the cylinder system for large reduced velocity as G∕D<0.7. A simple formula is used to explain the sub-harmonic resonance. The vortex shedding mode and the frequency of the lift force on the cylinders in the lock-in regime are used to validate the formula. The smaller the gap ratio is, the more lock-in regimes can be excited, and the higher-order sub-harmonic resonance can be observed. The control rod has a great influence or even is decisive on the VIV of the cylinder system at small gap ratio. As the gap ratio increases, the effect of the control rod is becoming weak. Besides the natural frequency of the cylinder system, the frequency corresponding to the vortex shedding mode is observed in the lift coefficient of the cylinders.

Simulation of vortex-induced vibrations of a cylinder using ANSYS CFX rigid body solver

This article simulates the vortex-induced oscillations of a rigid circular cylinder with elastic support using the new ANSYS CFX rigid body solver. This solver requires no solid mesh to setup FSI (Fluid Structure Interaction) simulation. The two-way case was setup in CFX only. Specific mass of the cylinder and flow conditions were similar to previous experimental data with mass damping parameter equal to 0.04, specific mass of 1 and Reynolds number of 3800. Two dimensional simulations were setup. Both one-degree-of-freedom and two-degree-of-freedom cases were run and results were obtained for both cases with reasonable accuracy as compared with experimental results. Eight-figure XY trajectory and lock-in behavior were clearly captured. The obtained results were satisfactory.

Implementing Vibration Framework for Simulation of VIV on Rigid Pier by SPH

It is worth mentioning that the effect of waves on fixed and floating platforms is considered as an important element when designing any offshore structures. This paper is developed a numerical model to simulate current and wave interaction with a vertical cylinder as a platform leg using Smooth Particle Hydrodynamics (SPH) method for solving hydrodynamics part and using Finite Element Method (FEM) for structural part. SPH method is Lagrangian meshless based which is accurate enough for free surface modeling in comparison with other Eulerian mesh based methods. Capability of this method to calculate inline and cross flow forces on cylinder taking into consideration different time solution algorithms. The results showed that SPH not only creates much better result for simulating Vortex Induced Vibration (VIV) but also using the predictor-corrector algorithm for time step algorithm can leads to the most accurate results for predicting lift force.

Numerical study of vortex-induced vibration of pivoted cylinders

This study was motivated by an idea of harvesting abundant renewable energy in the ocean currents. In order to capture the energy in the ocean currents, vortex-induced vibration (VIV) is exploited and a new configuration of a cylinder is considered. In particular, we investigate numerically the effect of the cross-sectional shape of a cylinder on VIV, when the cylinder is pivoted at a point in the wake. Three different cross-sectional shapes are tested in this study; their ratios of the minor axis to the major axis are 0.6, 0.8 and 1. We compare numerically hydrodynamic drag and lift forces on the stationary elliptic cylinders. The VIV simulations of these three cylinders show that two ellipses with smaller ratios have two times larger displacements than the circular cylinder with ratio 1. Such a superior performance of the elliptic cylinders is observed over a wide range of reduced velocities. A simplified model of a pivoted cylinder is analyzed to confirm that drag forces contribute positively to excitation torques and consequently VIVs. In order to take advantage of the drag forces which work favorably on VIVs, the pivot should be placed in the wake.

Modeling and Simulation of Vortex Induced Vibration on the Gas Transporting GRP Pipeline Riser

Modeling and Simulation of Vortex Induced Vibration on the Gas Transporting GRP Pipeline Riser

Numerical Simulation of Vortex-Induced Vibration with Three-Step Finite Element Method and Arbitrary Lagrangian-Eulerian Formulation

Numerical simulations were performed in this paper to investigate an elastically mounted circular cylinder subjected to vortex-induced vibration (VIV). A three-step finite element method (FEM) is introduced for solving the incompressible fluid flow equations in two dimensions. The computational procedure is coupled with a mesh movement scheme by use of the arbitrary Lagrangian-Eulerian (ALE) formulation on account of the body motion in the flow field. On running the numerical simulations, the Reynolds number was kept constant of Re = 100 and the reduced velocity [Formula: see text] = U/([Formula: see text] D) was varied from 3.0 to 10.2 by changing the natural frequency [Formula: see text] of the cylinder. The mass ratio m* = 4m/ρπD2 and damping ratio ξ are set to be 10.0 and 0.01, respectively, where U is free-stream velocity, D the diameter of the circular cylinder, m the mass of the cylinder per unit length, and ρ the density of the fluid. Numerical results are examined for the response amplitude of transverse direction as well as the phase angle, φ, between the lift force and the transverse displacement of the cylinder. The numerical results reveal that the transverse amplitudes present only two branches, namely, initial branch and lower branch, rather than three branches as the results obtained from high-Re experiments with low m∗ξ. On the other hand, the phase angles present almost linear increase with the reduced velocity in the synchronization region. However, experiments concerned with high Re exhibit a sudden jump in phase angle of approximate [Formula: see text]. The difference between the present study and the high-Re experiment is attributed to no substantial vortex shedding mode transition at the present numerical results of laminar flow.