Vortex-induced Vibration Mitigation Research Articles

An amplitude-dependent nonlinear approach for vortex-induced vibration evaluation of long-span bridges with inhomogeneous cross-sections

In the design of modern long-span bridges, inhomogeneous cross sections are increasingly used to meet various requirements, posing challenges in the investigation of vortex-induced vibration (VIV). This paper introduces a nonlinear approach with a focus on amplitude dependency in VIV for inhomogeneous bridges. It presents an inhomogeneous vortex-induced force model with amplitude-dependent parameters to capture spanwise variations in aerodynamics. These parameters are identified through multiple sectional wind tunnel tests. VIV amplitudes are determined by searching for solutions under the zero-damping condition for VIV. An illustrative bridge with an inhomogeneous fairing design is employed as an engineering application. The approach is rigorously validated with experimental data and applied to assess the prototype VIV behavior of the bridge with different fairing lengths. An optimal fairing length, constituting 40% of the main girder length in the mid-span, is identified to strike a balance between VIV performance and material usage. Discussion for the prediction results provides insights into the effects of fairing length inhomogeneity on VIV. In practice, deploying fairings in the large mode shape sections of the main girder achieves VIV mitigation comparable to a full-span installation.

Robust damping improvement against the vortex-induced vibration in flexible bridges using multiple tuned mass damper inerters

The tuned mass damper inerter (TMDI) is considered as one of countermeasures to mitigate the very-low-frequency vertical bending vortex-induced vibration (VIV) in flexible bridges. However, the control robustness of the TMDI against the system uncertainty is a serious concern due to the limited inerter span capacity. In this paper, the multiple tuned mass damper inerter (MTMDI) is used instead of identical TMDIs to provide a robust equivalent damping ratio against the uncertain VIV within the entire lock-in wind speed range. A design framework of the MTMDI considering the inerter span length is proposed based on a universal VIV model suitable for the fully closed, centrally slotted, and semi-closed box decks. In the framework, the fluctuation of VIV characteristics with the wind speed, the probability of occurrence of the VIV, and the uncertainties in VIV characteristics and deck dynamics are considered, simultaneously. Two objection functions are defined to focus on the maximizing the equivalent damper ratio and reducing the VIV mitigation failure, respectively. Finally, numerical analysis of a flexible bridge-MTMDI system subjected to the VIV is performed. The results show that the wind speed probability distribution plays a role of weighting coefficient in the MTMDI optimization. The choice of the objective function depends on the mass ratio of the MTMDI and the level of the system uncertainty. The well-optimized MTMDI achieved a more robust control result than the TMDI within the entire lock-in wind speed range.

Study on VIV performance of streamlined steel box girder of a sea-crossing cable-stayed bridge

The frequent occurrence of vortex-induced vibrations (VIVs) poses significant challenges for the operations of large-span sea-crossing bridges subjected to wind loads. A wind tunnel test device for large-scale section models is developed for a sea-crossing bridge to investigate the VIV performance of a streamlined box girder. A new type of aerodynamic countermeasure combining horizontal stabilizers and deflectors is proposed to address vertical and torsional VIV mitigation. To achieve optimal control effects, adjustments are made to the layout of deflectors and the width of horizontal stabilizers. The effects of varying structural damping ratios and low turbulence on vertical VIVs are also thoroughly examined. The VIV triggering mechanism of the girder by maintenance rails is revealed through numerical simulations using the Shear Stress Transport (SST) k−ω model. Finally, the suppression mechanism of the countermeasures is elucidated. The instantaneous vorticity distribution indicates that implementing the countermeasures effectively reduces the size of alternating shedding vortices on the trailing edge of the main girder. This research provides valuable insights into the VIV mitigation of streamlined box girders.

Shaping bridge decks for VIV mitigation: A wind tunnel data-driven adaptive surrogate-based optimization method

Vortex-induced vibration (VIV) of deck girders frequently drives the wind-resistant design of wind-sensitive bridges from the preliminary to final design stages. Shaping bridge decks is a proven strategy to mitigate VIV. While significant shape modifications are commonly restricted to preliminary design stages, only minor medications are possible at advanced design stages, typically involving adding flow modifiers or changing the shape and location of existing appendages. These mitigation strategies have been implemented in the last decades by carrying out expensive wind tunnel campaigns and following heuristic design rules. This paper proposes an experimental data-driven adaptive surrogate-based optimization approach to systematically identify optimum deck shapes that minimizes the economic cost of the bridge while fulfilling the VIV project specifications. The methodology is conceived to carry out simultaneously the general and detailed shape design of the final deck configuration by harnessing a sequential sampling plan aiming at reducing the sectional model construction costs. The proposed holistic design framework is successfully applied to a real application case involving 26 wind tunnel tests of 1.8-meter wide sectional models to figure out the optimal gap distance and location of maintenance tracks of a twin-box deck equipped with all the appendages included in the final deck design.

Benchmarking of VIV numerical analysis with prototype response for fatigue assessment of inverse catenary coldwater pipelines

High density polyethylene pipe has been used to draw coldwater for low temperature thermal desalination plants since the year 2006 at Lakshadweep Islands, India. The pipeline endured in-line oscillations due to shear current in one of the desalination plants, and this gave an opportunity to observe the response parameters of the prototype pipeline. The recorded oscillation parameters are utilized as a benchmark to verify the results of the vortex induced vibration (VIV) analysis in frequency domain and time domain, and the results show good concurrence. The in-line fatigue damage assessment is carried out for a range of current profiles showing the need for mitigation of pipeline VIV. The helical strakes on a partial length of the pipeline is modeled numerically showing significant suppression of VIV response as well as substantial increase in fatigue life of the pipeline. The benchmarking of the VIV response analysis with prototype measurements enhances the reliability of using numerical VIV fatigue analysis and mitigation measures.

Influence of the installation of a trailing edge flap on the vortex induced vibrations of a wind turbine blade

This work explores the use of a trailing edge flap for the mitigation of the Vortex Induced Vibrations (VIV) of a wind turbine blade in standstill. Fluid structure interaction simulations are performed, coupling a computational fluid dynamics code with a multi-body structural solver. A publicly available 96 m long wind turbine blade is selected for the study, and labeled as IEA 10MW. The effects of a flap actuation in the range [−90°, 90°] are analyzed, for a given set of inflow conditions, and compared to the aeroelastic response of the original IEA 10MW geometry. While the consideration of the flap does lead to reductions on the amplitude of the edgewise vibrations, these are only noticeable when operating outside of the design limits of the aerodynamic device. A simple non-dimensional analysis seems to indicate that the potential of the flap installation with regards to VIV mitigation is very limited, as the instability is only shifted towards different inflow conditions and the expected effects on the maximum amplitude of vibrations are minor.

Aerodynamic mechanism of triggering and suppression of vortex-induced vibrations for a triple-box girder

With the objective of exploring the aerodynamic mechanism of triggering and suppression of vortex-induced vibration (VIV) for a triple-box girder, wind tunnel tests involving both static and dynamic pressure measurements, as well as CFD simulation for flow visualization were carried out on a bare girder. Both vortex-induced vibrations and surface pressures were obtained from static and dynamic sectional model tests for three typical wind incidence angles, namely α = 0°, +3°, and −3°. Results indicated that vortices shed regularly from the downwind sides of both windward box and middle box, then impinged on the upwind sides of middle box and leeward box respectively, resulting in prominent fluctuating pressures here, which was likely to render the triple-box girder more susceptible to VIV. Specifically, fluctuating lift of middle box was the main trigger of VIV at wind incidence angle α = +3°, while that of leeward box was the main trigger at α = 0° and −3°. The regular vortex shedding and impinging process could be effectively suppressed by the grid plates over girder slots, which was favorable to VIV mitigation. When VIV occurred, self-excited force became the main component of the fluctuating force, and it could be the major driver of the large-amplitude oscillation.

Parameters optimization and performance evaluation of multiple tuned mass dampers to mitigate the vortex-induced vibration of a long-span bridge

Vortex-induced vibration(VIV) is one of the primary dynamic problems of long-span bridges, which affects the safety and serviceability of bridges. The control and mitigation of VIV is a hotspot to researchers. Multiple tuned mass dampers(MTMD) consist of a set of tuned mass dampers(TMD) with varied frequencies and damping ratios, which is a common method for vibration control of structures. In this study, a concept of complex effective mass is proposed, which can entirely represent the dynamic effect of MTMD on bridges, and a derivative-based MTMD optimization process for VIV control of long-span bridges is presented. The VIV mitigation of a six-span continuous steel box-girder bridge is used to analyze the performance and mechanism of MTMD from the aspects of frequency domain and time domain. Optimal parameters of MTMD for suppressing VIV are obtained by the proposed algorithm. The results indicate that MTMD can significantly reduce the displacement amplitude of the beam due to VIV, and the performance of MTMD is better than that of single tuned mass damper(STMD) with the same mass ratio. The optimal performance of MTMD is independent of the mass distribution of the sub-TMDs. Moreover, the damping ratio of MTMD is much lower than that of STMD, but it can still help the vibration of the primary structure to decay faster. Complex mode theory and transfer function theory are used to explain this phenomenon. It indicates that the performance of MTMD does not depend on its damping ratio but is due to the phase interference between complex modes, and a one-way energy barrier between the bridge deck and MTMD can be formed, which prevents the transfer of vibration energy from MTMD to the primary structure after unloading. Finally, the stroke of MTMD in the control of long-span bridge VIV is analyzed, and a simplified formula is proposed.

Experimental investigation on vortex-induced vibrations of a triple-box girder with web modification

Split type box girder is a recommendable structural style for long-span cable-supported bridges due to its excellent aeroelastic stability. A major issue of this kind of girder is its susceptibility to vortex-induced vibration (VIV), which has not been adequately investigated. This paper presents an experimental study on VIV of a triple-box girder with three different web modifications (namely curved web and linear-type webs with different slopes). Both small- and large-scale sectional models were employed for wind tunnel tests considering the Reynolds number effect. Results indicated that the triple-box girder showed poor VIV performances in both construction and completed phases. Generally, linear-type web was superior to curved web in terms of VIV performance. Increasing the structural damping and turbulence intensity of incoming flow were helpful for VIV mitigation. Geometric profiles and arrangement of appurtenant facilities on the girder have significant effects on the VIV performance. Aerodynamic optimal schemes were proposed for VIV mitigation both in construction and completed phases. Obvious discrepancies in VIV responses were observed between the small- and large-scale tests for several scenarios. Possible factors being responsible for the discrepancies were Reynolds number, turbulence intensity, nonlinearity of model structural damping, blockage ratio and geometric accuracy of the sectional models.

Prediction and Suppression of Vortex-Induced Vibration for Steel Tubes with Bolted Joints in Tubular Transmission Towers

In this paper, a series of full-scale wind tunnel tests are conducted to study the vortex-induced vibration (VIV) of the steel tubes connected with C-shaped bolted joints. The dynamic properties of VIV responses of the steel tubes are analyzed and discussed in terms of probability density functions (PDFs) and power spectral density (PSD) functions. Based on the wind tunnel test results, a new empirical formula is derived to estimate the VIV critical wind speed of the tube with C-shaped joints, and an improved model is developed to predict the maximum VIV response of the steel tube. The proposed models are further validated through an independent wind tunnel test. In order to suppress excessive VIV responses of steel tubes, a passive vibration control approach is employed by installing a discrete cross-fin spoiler (DCFS) in various designs on the testing tubes. Key design factors of the DCFS, which are related to the VIV suppression effectiveness, are studied through wind tunnel tests, and the relatively optimal design of DCFS is recommended for VIV mitigation.

Mitigation of Vortex-Induced Vibration of Cylinders Using Cactus-Shaped Cross Sections in Subcritical Flow

Flexible cylinders, such as marine risers, often experience sustained vortex-induced vibrations (VIVs). Installing helical strakes on a riser is the most widely used technique to mitigate VIVs. This study was inspired by the giant Saguaro Cacti which can withstand strong wind with a shallow root system. In this study, numerical simulations of flow past a stationary cylinder of a cactus-shaped cross-section in a two-dimensional flow field at a subcritical Reynolds number of 3900 were performed. Results show that cylinders of a cactus-shaped cross-section have a lower lift coefficient without increasing drag compared to those of a circular cylinder. VIV experiments on a single flexible pipe as well as on a set of two tandem-arranged flexible pipes were conducted at different reduced velocities to investigate the effects of the streamwise spacing and wake of the cactus-like body shape on VIV mitigation. Experimental results show that the cactus-like body shape can mitigate VIV responses of the cylinder at upstream position with no cost of increased drag; however, similar to helical strakes, the efficiency of VIV mitigation for the cylinder at downstream position is reduced. Although the cactus-like body shapes tested in this study were not optimized for oscillation suppression, still this study suggests that modification of the cross-sectional shape to a well-designed cactus-like shape has potentials to be used as an alternative technology to mitigate VIV of marine risers.

Experimental study of cactus-like body shape on flow-induced vibration mitigation of clustered cylinders

Abstract Vortex-Induced Vibration (VIV) is a major contributor to the fatigue damage of marine risers which are often arranged in an array configuration. In addition to helical strakes and fairings, studies have been strived in searching for possible VIV suppression techniques. Inspired by giant Saguaro Cacti, flexible cylinders of different cactus-shaped cross sections were tested in a water tunnel facility, and test results showed that cactus-like body shapes reduced VIV responses of a cylinder at no cost of significant increase of drag. A series of experiments were conducted on a pair of two tandem-arranged flexible cylinders and an array of four cylinders in a square configuration to investigate the effects of wake on the dynamic responses of cylinders and the VIV mitigation effectiveness of the cactus-like body shape. Results showed that the cylinders in a square configuration, either at the upstream or downstream positions, might have larger dynamic responses than those of a single cylinder. The cactus-like body shape could mitigate VIV responses of cylinders at upstream positions in an array configuration; however, similar to helical strakes, the mitigation efficiency was reduced on downstream cylinders. Note that the cactus-like cross-sectional shape investigated was not optimized for VIV suppression. The present study indicates that the modification of the cross-sectional shape of a cylinder to a well-designed cactus-like shape may be used as an alternative technique to mitigate the VIV of marine risers.

An elastic rotative nonlinear vibration absorber (ERNVA) as a passive suppressor for vortex-induced vibrations

Vortex-induced vibration (VIV) is a self-excited and self-limited flow-induced vibration phenomenon of importance for both the academic and the technological communities. Particularly for the offshore engineering scenario, VIV plays an important role in the structural fatigue analysis. Hence, VIV suppression is a relevant topic. Among different solutions for VIV mitigation, this paper focuses on the numerical analysis of an elastic rotative nonlinear vibration absorber (ERNVA) as a device for passive suppression. The ERNVA consists of a mass placed at the tip of an axially elastic beam hinged to the cylinder by means of a linear dashpot. In this paper, the hydrodynamic loads are calculated using a wake-oscillator model, allowing comprehensive parametric studies for assessing the influence of the ERNVA parameters on its efficiency for the whole range of reduced velocities associated with the lock-in. Among other novel results, it is found that ERNVA can lead to a $$25\%$$ decrease in the maximum oscillation amplitude, being significantly more efficient than its counterpart characterized by a rigid rotating arm. Passive suppression is obtained not only for the peak, but within a certain range of reduced velocities. Curves showing the influence of the ERNVA parameters on the force coefficients for different values of reduced velocity are also innovative.

Aerodynamic performance of Π-shaped composite deck cable-stayed bridges including VIV mitigation measures

This study systematically investigates the influence of the cross-sectional aspect ratio (B/H) and four different aerodynamic mitigation measures, i.e., the fairing, lower central stability plate, inverted L-shaped edge plate, and lower horizontal edge plate, on the performance of cable-stayed bridges, with π-typed composite deck, i.e., π section, due to vortex-induced vibrations (VIV). The study utilized wind tunnel tests and limited CFD simulations by varying bridge dimensions. First, based on a survey of existing cable-stayed bridges with the π-typed composite deck, three-section models with different aspect ratios were studied and their corresponding vibration characteristics for the vertical and torsional VIVs were analyzed. Then, the vibration suppression effects of mitigation measures with several variants in shape were investigated to determine an effective mitigation measure, i.e., with favorable aerodynamic stability, for the π section deck. The vibration suppression mechanism for three selected cases was further assessed using numerical simulation. The results show that: (a) for the π section model with the aspect ratio in the range of 9.05–11.96, increasing the ratio value will delay the onset wind speed of the vertical and torsional VIVs; (b) In the case of a low ratio of the torsional frequency to vertical bending frequency, there are often special phenomena where the vertical and torsional vibrations coexist. However, a larger aspect ratio would result in more independent vertical and torsional vibrations; (c) Regarding the vibration suppression effect, based on the limited studied cases, a small fairing can be superior to large fairings; (d) Different forms of the lower central stability plate have a good suppression effect on the vertical VIV; (e) The use of inverted L-shaped edge plate with a ​= ​23H and b ​= ​12H is identified to result in the best vibration suppression for both the vertical and torsional vibrations among the considered mitigation measures, where a and b are the size parameters of the inverted L-shaped edge plate; and (f) The lower horizontal edge plate cannot effectively improve the torsional VIV performance. This study offers guidance on the performance of composite cable-stayed bridge with the π section in isolation and equipped with mitigation measures to aid in the engineering design practice.

Vortex generator’s effect on trailing edge vortex shedding and fluid structure interaction

An initial study of the effects vortex generators (VGs) have on the mitigation of vortex-induced vibrations (VIVs) of hydrofoils have been performed at the Waterpower laboratory of the Norwegian University of Science and Technology. The VGs are placed close to the trailing edge of a blunt hydrofoil. Reasonable design parameters of the VGs were found from the literature with regard to which would induce the strongest vortices with the lowest drag. Vibration frequencies of the hydrofoil were measured using flush mounted strain gauges located close to the trailing edge. This paper presents the design of the VGs and some initial results of the experiments performed with these devices. The preliminary results indicate a possible mitigation of VIVs. This could be because of the interference between the primary vortices generated by the hydrofoil and the longitudinal vortices generated by the VGs, but further work is necessary to make a conclusion.

Parameter determination of the tuned mass damper mitigating the vortex-induced vibration in bridges

This paper investigates the parameter determination of the tuned mass damper (TMD) for mitigating the vortex-induced vibration (VIV) in bridges. At present, there is no consensus on design formulas for the TMD in the VIV mitigation. An equivalent damping ratio is proposed to characterize the TMD contribution to the VIV mitigation based on a semi-empirical nonlinear model. The effects of the uncertainties in aerodynamic parameters and structural parameters on the control effect of the TMD are studied. Three typical design formulas for the TMD are compared from the perspective of the effectiveness, robustness, and reliability. The results show that the equivalent damping ratio depends only on the TMD parameters and is sensitive to the uncertainty in the stiffness of the bridge. The vortex-induced amplitude at lock-in is moderate to the uncertainties in aerodynamic parameters. The design formulas for the free-vibration suppression are the most robust option that avoids a high probability of failure, which are recommended for the TMD mitigating the VIV in bridges. At last, a numerical example of the deep-water non-navigable bridge of the Hong Kong-Zhuhai-Macao Bridge is performed to confirm the rationality of the suggested design formulas.

Experimental investigation on multi-mode vortex-induced vibration control of stay cable installed with pounding tuned mass dampers

In this paper, pounding tuned mass dampers (PTMDs) were designed to mitigate the multi-mode vortex-induced vibration (VIV) of stay cable utilizing the viscous-elastic material\'s energy-dissipated ability. The PTMD device consists of a cantilever metal rod beam, a metal mass block and a specially designed damping element covered with viscous-elastic material layer. Wind-tunnel experiment on VIV of stay cable model was set up to validate the effectiveness of the PTMD on multi-mode VIV mitigation of stay cable. By analyzing and comparing testing results of all testing cases, it could be verified that the PTMD with viscous-elastic pounding boundary can obviously mitigate the VIV amplitude of the stay cable. Moreover, the installed location and the design parameters of the PTMD device based on the controlled modes of the primary stay cable, would have a certain extent suppression on the other modal vibration of the stay cable, which means that the designed PTMDs are effective among a large band of frequency for the multi-mode VIV control of the stay cable.

Vortex-induced vibrations mitigation through a nonlinear energy sink

The passive suppression mechanism of the vortex-induced vibrations (VIV) of the cylinder by means of an essentially nonlinear element, the nonlinear energy sink (NES) is investigated. The flow-induced loads on the cylinder are modeled using a prevalent van der Pol oscillator which is experimentally validated, coupling to the structural vibrations in the presence of the NES structure. Based on the coupled nonlinear governing equations of motion, the performed analysis indicates that the mass and damping of NES have significant effects on the coupled frequency and damping of the aero-elastic system, leading to the shift of synchronization region and mitigation of vibration responses. It is demonstrated that the coupled system of flow-cylinder-NES behaves resonant interactions, showing periodic, aperiodic, and multiple stable responses which depend on the values of the NES parameters. In addition, it is found that the occurrence of multiple stable responses can enhance the nonlinear energy pumping effect, resulting in the increment of transferring energy from the flow via the cylinder to the NES, which is related to the essential nonlinearity of the sink stiffness. This results in a significant reduction in the VIV amplitudes of the primary circular cylinder for appropriate NES parameter values.

Analysis of Flow over a Circular Cylinder Fitted with Helical Strakes

The effectiveness of the helical strakes in suppressing the vortex-induced vibration (VIV) of a rigid cylinder is investigated by providing a three start helical strakes around a circular cylinder at two Reynolds numbers (100&28000). While the effect of helical strakes on suppression of vortex shedding has been studied extensively, the mechanism of VIV mitigation using helical strakes is much less well documented in the literature. In the present study, a rigid circular cylinder of diameter d=40mm attached with three-strand helical strakes of dimensions of 10d in pitch and 0.15d in height was tested by simulation. To numerically simulate vortex shedding, CFD is used to calculate the unsteady flow that arises from a fluid moving past an obstruction. A computational grid independence study has been done for flow over the circular cylinder and the grid resolution in which there is faster recovery of coefficient of lift is taken for the simulation. The contours of static pressure, velocity magnitude and vorticity magnitude and the hydrodynamic coefficients Cd and CL are obtained. It is found that, as expected, the straked cylinder has a higher drag coefficient in comparison with a smooth bare cylinder. The helical strakes can reduce VIV by about 99%.

Investigation on the effectiveness of helical strakes in suppressing VIV of flexible riser

The effectiveness of the strakes in suppressing the vortex-induced vibration (VIV) of a long flexible cylinder is investigated by varying the pitch (p) and height (h) of the strakes. Measurements of cross-flow (CF) vibration amplitude, in-line (IL) and CF frequency responses, and hydrodynamic forces are presented for low mass flexible cylinders with helical strakes. Cylinders with aspect ratio of 162 were applied with constant pre-tension to restrict the vibration in IL and CF directions. Six cases with about 180 runs were executed under subcritical Reynolds number (Re = 0.144to 1.384) of uniform flow. Calculation on the laminar boundary layer thickness around a circular cylinder was performed as a benchmark in deciding the height of strakes. Present study shows that at certain strakes’ height which is larger than the laminar boundary layer thickness, significant VIV mitigation is found. However, the suppression effectiveness of helical strakes on flexible cylinder is less notable compared to a rigid cylinder. The change on pitch of strakes affects the occurrence of lock-in region and prevents the frequency to switch into higher mode. On the other hand, increase on the height of strakes narrows the lock-in region and plays the most major role in suppressing the vibration of a cylinder. The hydrodynamics forces indicate an unexpected phenomenon where the bare cylinder possesses higher force coefficients compared to cylinders with helical strakes. However, large drag penalty is still found in a particular case at higher reduced velocity. The most effective configuration of strakes in terms of the dynamic responses is p = 10D and h = 0.15D model. However, model of p = 10D and h = 0.10D performs better in reducing the hydrodynamic forces.