Wind-induced Vibration Research Articles

Studying the wind-induced vibrations of a traffic signal structure through long term health monitoring

Recent failures of traffic signal structures have showcased the vulnerability of such structures to wind loading. During the wind-induced vibration of the mast arm, the large mass of the mast arm creates high-level stress at the pole-to-arm connection. Additionally the low mechanical damping results in accumulationof stress cycles ewhich could cause fatigue damage at the pole-to-arm connection. In this study, a traffic signal structure with three vertical traffic lights was selected for long-term health monitoring. The monitored acceleration data at the mast arm tip was used to study the wind-induced behavior and was compared with the theoretical analysis results. The monitored strain data at the pole-to-arm connection was used to evaluate the fatigue damage. Low stress ranges were recorded most of the time, which indicates that the wind-induced fatigue damage might not be a significant concern for the monitored traffic signal structure. However, high stress ranges have been recorded at high wind speeds, indicating fatigue damage can still be an issue at higher wind speed regions. The performance of monitored traffic signal structure was compared with those in the literature. An apparent discrepancy was noticed between their wind-induced behaviors, and the orientation of the attached traffic lights was identified as a key parameter to influence the wind-induced behavior. It was found that at low wind speed, attached vertical traffic lights can reduce the likelihood of vortex-induced vibration and, as a result, lower the stress range at the pole-to-arm connection.

Influence of the Flexible Tower on Aeroelastic Loads of the Wind Turbine

The finite element discretization of a tower system based on the two-node Euler-Bernoulli beam is carried out by taking the cubic Hermite polynomial as the form function of the beam unit, calculating the structural characteristic matrix of the tower system, and establishing the wind turbine-nacelle-tower multi-degree-of-freedom finite element numerical model. The equation for calculating the aerodynamic load for any nacelle attitude angle is derived. The effect of the flexible tower vibration feedback on the aerodynamic load of the wind turbine is studied. The results show that, when the stiffness of the tower is large, the effect of having tower vibration feedback or not on the aeroelastic load of the wind turbine is small. For the more flexible tower system, wind-induced vibration time-varying feedback will cause larger aeroelastic load variations, especially the top of the tower overturning moment, thus causing a larger impact on the dynamic behavior of the tower downwind and crosswind. As the flexibility of the tower system increases, the interaction between tower vibration and pneumatic load is also gradually increasing. Taking into account the influence of flexible towers on the aeroelastic load of a wind turbine can help predict the pneumatic load of a wind turbine more accurately and improve the efficiency of wind energy utilization on the one hand and analyze the dynamic behavior of the flexible structure of a wind turbine more accurately on the other hand, which is extremely beneficial to the structural optimization of wind turbine.

Exploring energy harvesting and vibration mitigation in tall buildings accounting for wind and seismic loads

With the changing climate and the limited supply of fossil fuels available for global energy use, much research has been done to develop innovative methods of producing clean and renewable energy. Out of the various energy sources, wind forces can cause tall buildings to undergo significant vibrations presenting a potential source of clean and renewable energy for buildings and the power grid. To mitigate wind-induced vibrations in tall buildings, viscous dampers have been widely utilized, which, unlike tuned-mass dampers, are also effective in mitigating earthquake-induced vibrations. Contrary to conventional designs, this research explores the use of energy harvesting transducers, in place of viscous dampers, as a means of not only mitigating vibrations under extreme loading conditions (e.g. earthquakes), but also harvesting energy from wind induced vibrations during service conditions and converting it to electricity. This research demonstrates the often conflicting requirements for supplemental damping related to energy harvesting (EH) from wind loads under service conditions vs. vibration mitigation (VM) under extreme events (e.g., earthquakes). Specifically, this research shows that large damping is usually required for VM, whereas small or moderate damping is often required to maximize EH. In doing so, this research develops, and validates using test data, a nonlinear model for an electromagnetic EH transducer, quantifies the EH potential of a selected tall building as a function of the supplemental damping and wind speed showing that EH power generation can reach kWs (as opposed to W), and assesses the seismic performance of the same building as a function of the supplemental damping for two seismic hazard levels. The findings of this research will support future studies pursuing the concept of energy harvesting in structural design.

Full Scale Experiment for Vibration Analysis of Ice-Coated Bundled-Conductor Transmission Lines

Full scale experiment has received increasing attention in recent years for the reliability analysis of power supplies and power systems. In this paper, the vibration behaviours of conductors with and without D-section ice coatings are addressed by virtue of a field test platform consisting of the prototype of a transmission tower-line system. Utilizing fibre Bragg grating sensors, the vibration of conductors under artificial displacement and natural wind excitations are monitored, and their dynamic characteristics are assessed by the spectral analysis and the identification technique of Hilbert-Huang transform. It is revealed that the vibrations of ice-free and ice-coated multi-bundled conductors vary wildly despite under similar artificial displacements and natural wind excitations. The vibration of ice-coated conductors is mainly dominated by their low-order modes, especially in the frequency range of 0.24–2.0 Hz; while the vibration of ice-free conductors gains more benefits from their high-order modes. Compared to the ice-free conductors, the conductors with eccentric ice coating are prone to suffer from galloping under specified wind attack angle; although their vibrations are still controlled by the low-order modes, yet the frequency values of the dominant modes have changed from one wind attack angle case to another. This kind of frequency modulation phenomenon indicates that nonlinear vibration characteristics of ice-coated conductors might change under different wind conditions, which brings great challenges to the research of wind-induced vibration characteristics of ice-coated conductors.

Wind-induced Vibration of High-rise Buildings and Its Countermeasures

This article analyzes the cause of the wind-induced vibration, points out its harm, and finally introduces some countermeasures of it nowadays. To commence, it introduces the phenomenon called Buffeting, Vortex-excited Vibration and Self-excited Vibration that leads to the vibration. Then, it concludes that the vibration will lead to structural damage and make its residents uncomfortable through analyses, indicating that the vibration can be controlled by structural optimizing, aerodynamic measuring and equipping energy dissipation systems. This article simply introduces their principle and application.

Role of dynamic water rivulets in the excitation of rain–wind-induced cable vibration: A critical review

It has been more than 30 years since Hikami Y and Shiraishi N (1988) Rain–wind-induced vibrations of cable-stayed bridges. Journal of Wind Engineering and Industrial Aerodynamics 29: 409–418 first reported the rain–wind-induced vibration (RWIV) of stay cables in the construction stage of Meikonishi Bridge, Japan. After that, considerable research efforts have been devoted to understanding the RWIV of stay cables, and the role of the upper rivulet has been gradually realized and studied. This study presents a selective review on recent progress of RWIV and its controversial excitation mechanism. The available knowledge and up-to-date understanding of this complex fluid-structure interaction are presented in some detail. The formation, dynamics of water rivulet, and its role in affecting the near-wall boundary layer properties and in the excitation scenario of RWIV are of particular interest in this study. Finally, some limitations of previous studies are concluded, with some perspective suggestions for further study of excitation mechanism of RWIV.

Wind-Induced Vibration of Traditional Chinese Citygate Buildings in the Ming-Qing Dynasties – A Case Study of the Nanjing Drum Tower

ABSTRACT Compared to normal traditional Chinese timber buildings, citygate buildings are relatively high, lightweight, and quite vulnerable to wind. The present work aims to carry out a wind-induced vibration study on a traditional Chinese citygate building, the Nanjing Drum Tower, with the method of computational fluid dynamics (CFD) simulation to determine the wind loads and finite element (FE) analysis to assess its structural response. The architectural and structural characteristics of traditional Chinese timber buildings in the Ming-Qing dynasties are analysed. The Nanjing Drum Tower has typical characteristics and is taken as the representative building in this study. The wind pressure coefficients of the drum tower are obtained by CFD simulation with the Reynolds-averaged Navier-Stokes (RANS) model. The structural response of the drum tower under wind loads is analysed based on FE analysis. The obtained results can provide a basis for assessing the wind-induced vibration of traditional Chinese citygate buildings.

Extracting Time-Varying Mean Component of Non-Stationary Winds Utilizing Vondrak Filter and Genetic Algorithm: A Wind Engineering Perspective

The time-varying mean (TVM) component plays a vital role in the characterization of non-stationary winds, whereas it is difficult to extract the TVM accurately or to validate it quantitively. To deal with this problem, this paper first develops two additional conditions for the TVM extraction from the perspective of structural wind-induced vibration response, then presents an approach, based on the combination of Vondrak filter and genetic algorithm (Vondrak-G), to derive the optimal TVM from non-stationary wind speed records as well as its turbulence characteristics (i.e. gust factor, turbulence intensity, and turbulence integral length scale). Furthermore, the wind characteristics obtained by the Vondrak-G approach are compared with those by a conventional approach derived for stationary winds, demonstrating that the results by the Vondrak-G approach are evidently more accurate. This paper aims to provide an effective method for accurately extracting the TVM and then evaluating wind characteristics of the non-stationary wind.

A Framework for Vibration Attenuation in Traffic Mast Arm Structures under Wind Loads

Traffic signals and information signs play a vivid role in maintaining safe travel by guiding drivers on highways and urban roads. Traffic mast arm structures are susceptible to vibrations induced by wind loads. Fatigue-induced failure is common in these structures. However, it is crucial to ascertain the functionality of signal support structures. This paper lays the foundation for a fully computational framework to model and mitigate wind-induced vibrations in traffic lighting support structures by conducting computational fluid dynamics (CFD) simulations, dynamic modeling, and damping enhancement. We validated the CFD simulations by aerodynamic testing. The dependence of flow pattern and aerodynamic loads on Reynolds number reveals the importance of full-scale CFD with large eddy simulation for wind load estimation on mast arm structures. Distributed tuned mass dampers were created by employing available weights of lighting boxes. The results show that distributed tuned lighting boxes are effective for vibration suppression. Besides, damping enhancement can significantly reduce vibration-induced stresses and hence extend the fatigue life. The proposed mitigation technique promises to save construction costs and improve the safety of the traveling public. The procedure followed for creating time histories of wind loads integrated with finite element modeling applies to other vibration lessening techniques for potential inclusion in the AASHTO standard.

FULL-SCALE EXPERIMENTAL TESTING TO INVESTIGATE WIND-INDUCED VIBRATIONS ON CURTAIN WALL SYSTEMS

Curtain walls are dominant cladding components of mid to high-rise buildings in modern architecture. However, the curtain wall systems have been observed highly susceptible to vibrations leading to component or system-level failure during recent extreme wind events. This paper studies the complex mechanisms of wind induced vibration (WIV) functionality at the system-and component-levels. A wind testing experiments for a full-scale single-skin façade panel was conducted at the Wall of Wind experimental facility (WOW EF) at Florida International University (FIU). Effect on the vibration of the curtain wall due to the addition of sunshade fin is also studied. The experimental protocol included testing the samples (with and without sunshade fins) at various wind speeds from 22.3 m/s to 40.1 m/s with 8.9 m/s intervals in open terrain. Effect of wind direction is also considered varying from 0 to 180 degrees with 45-degrees interval. The tests were performed on two sets of panels: (1) a polycarbonate panel (with the geometric properties maintained) to obtain dynamic wind pressure data; (2) actual glazing units that are instrumented with accelerometers and strain gauges at critical sensing locations. The experimental results indicate that the sunshade fins have a stiffening effect on the joints of the curtain walls while overall increasing the wind pressure on the panel. Dynamic amplifications on the glazing were in the order of 1.1 to 1.8 which underline the importance of studying dynamic effects on the façade systems.

Galloping vibration of stay cable installed with a rectangular lamp: Field observations and wind tunnel tests

In recent years, stay cables on cable-stayed bridges have been equipped with various kinds of lamps to lighten the cables at night. Large amplitude vibration of the stay cables of the Kuimen Bridge was observed after some rectangular lamps were installed. The mechanism and countermeasure of the cable vibration of this bridge were investigated in this paper. First, wind-induced responses of six stay cables were extracted from a video observed in the field. Second, according to Den Hartog's theory, a series of force measurement wind tunnel tests on stay cable attached with a rectangular box were carried out to test the possibility of galloping. Third, a series of vibration measurement wind tunnel tests based on 2-dimensional and 3-dimensional test models were carried out to reproduce the vibration of the cable-lamp test model. In the test, the features of wind-induced vibration were studied at the damping level of 0.1%, 0.3%, 0.6% and the inclination angles of the stay cable include 25°, 35°, 40°, and 45°. The results show that the rectangular aluminum alloy box of the lamp on stay cables can result in the unstable galloping vibration at a very low wind velocity. The critical wind velocity of the cable-lamp test model can be as low as 6.3 m/s (damping ratio ζ = 0.1%), which is a wind velocity often encountered. It appears that the critical wind velocity increases with the increase of the structural damping ratio, but is only 9–11 m/s when the damping ratio is 0.6%. It seems that increasing the damping ratio has little effect on suppressing the galloping of the stay cable. Finally, the rectangular aluminum alloy box of the lamp was removed and only an electrical wire was attached on the cable surface. The vibration measurement wind tunnel tests based on the 3-dimensional cable-wire test model indicate that the stay cable attached with an electrical wire is aerodynamically stable if the position angle of the wire is 0°, which is consistent with the actual situation.

Flow around square-like cylinders with corner and side modifications

Shape modification effectively reduces the wind loading and wind-induced vibrations of slender structures. Large-eddy simulation is used to investigate the flow around multiple square-like cylinders at a Reynolds number of 22,000. Based on a standard square cylinder, six square-like cylinders are simulated with sharp/rounded corners and straight/concave/convex sides. The combination of rounded corners and convex sides enables the best aerodynamic performance. Furthermore, a parametric study on the round-convex cylinder is conducted considering a fixed corner radius and various side curvatures B/K (B: nominal side length; K: side radius). The results show that both the aerodynamic characteristics of and the flow features around the cylinder change considerably with varying B/K and that three distinct flow regimes are observed. In Stage I (0 ≤ B/K ≤ 0.71), the flow separates at the front corners, and the aerodynamic forces decrease gradually. In Stage II (0.71 < B/K < 1.00), the shear layer separating at the front corner-side region reattaches to the lateral sides. The fluctuating coefficients rise at B/K = 0.74; thereafter, the aerodynamic forces drop and are minimized at B/K = 1.00. In Stage III (1.00 ≤ B/K ≤ 1.77), flow separates at the lateral sides, and the aerodynamic forces recover gradually.

Wind-induced vibration mitigation of video screen rooms in high-rise buildings

Video walls, made of closely spaced video screen systems, are currently very used in architecture and interior design applications. To have a continuous image, the gaps between the screens must be limited as much as possible and the vibration of the supporting structure must be reduced to avoid ponding and consequent screens damage. The problem is particularly important when video walls are in rooms inside high-rise buildings that, due to their high deformability, experience significant wind-induced drifts and accelerations. In this case, it is convenient to mount video screens on a three-dimensional lightweight frame substructure (video wall room), supported by the building’s floor. To ensure the limitation of the relative displacements between the screens in case of strong winds, the substructure can be equipped with base isolators capable of mitigating the global response when the buildings’ induced accelerations overcome specific thresholds. This paper is aimed at investigating the wind-induced response of video screen rooms located inside wind-excited high-rise buildings and at providing guidance for the design of the base isolation devices. The floors’ accelerations measured during aeroelastic wind tunnel tests on a high-rise building are applied as base accelerations to a finite element method model of the video room. The parameters of the constitutive behavior of the base isolation system are optimally calibrated as a function of the wind speed and position over the building height.

Aerodynamic characteristics of a square cylinder with corner fins

This paper investigates the effect of fitting fins at the corners of a square cylinder on aerodynamic characteristics of the cylinder via wind tunnel tests and large eddy simulations (LES). Although it has been recognized that the corner fins have a remarkable effect on aerodynamic characteristics of a square cylinder, no study has been carried out to systematically evaluate this effect and reveal the underlying mechanism. Three types of corner fin configurations, i.e. fins fitted only to the leading corners, fins fitted only to the trailing corners, and fins fitted to both leading and trailing corners were studied. It was found that the corner fins significantly influence aerodynamic characteristics, such as mean drag coefficient, fluctuating lift coefficient, and vortex shedding of the cylinder. The influences of these corner fin configurations are very different. In general, the leading and trailing fins have an opposite effect on these characteristics. The mechanisms underlying these effects were clarified based on the flow regime visualized via LES. The interesting findings have practical significances not only for reducing aerodynamic forces and wind-induced vibration of infrastructures, but also for enhancing wind-induced vibration-based energy harvesting.

Response control of wind turbines with ungrounded tuned mass inerter system (TMIS) under wind loads

Wind turbine towers are sensitive to wind loads and lose efficiency when suffering excessive wind-induced vibrations. Structural control techniques such as tuned mass dampers (TMD) can be used to reduce the vibration response of the tower. However, the additional mass of this system would occupy a large amount of space within the wind turbine device, which can inconvenience installation and maintenance. An inerter is a high-efficiency two terminal mechanical element for vibration control with the characteristic of mass and damping enhancements. An ungrounded tuned mass inerter system (TMIS) –composed of a tuned mass, a tuned spring and an inerter subsystem – has potential to control wind-induced vibration efficiently. In this study, a simple design method for wind turbine towers equipped with a TMIS under wind loads is proposed, based on structural performance demand as well as control cost. A 1.5 MW wind turbine tower benchmark model is adopted to exemplify the proposed design method. Comparative analyses are conducted between a conventional TMD and the TMIS. Results show that the TMIS can achieve the same vibration control effect as the TMD while using a smaller tuned mass. A sensitivity study of the TMIS is also carried out to investigate the impact of mechanical element parameters on the performance of the vibration mitigation system. It is concluded that the optimal designed TMIS has the advantage of lightweight tuned mass over TMDs in wind-induce vibration control of wind turbine towers.

Optimal Design of Mega-Frame Core Wall Structures Equipped with Viscous Damped Outriggers for Human Comfort Performance under Wind Loading

Megatall and supertall buildings often adopt megastructure systems characterized by secondary structure systems, and the serviceability problem caused by wind-induced vibrations often becomes the dominant factor in the structural design. Because the deformation of a supertall building usually presents bending characteristics, a viscous damped outrigger can reduce the wind-induced vibration of a supertall building with the installation of a small number of viscous dampers. However, time history analysis of the prototype model considering the nonlinear characteristics of viscous dampers is time-consuming, which is not conducive for iterative design optimization. Additionally, the conventional simplified model composed of one cantilever beam cannot be used for the analysis and design of a viscous damped outrigger. In this study, a simplified wind-induced vibration prediction model is proposed based on the mechanical characteristics of megastructures. This simplified model is a plane model that includes both core walls and frames whose member size can be extracted from the original structure. Parametric analysis shows that the simplified model has high acceleration prediction accuracy. An optimal design method combined with the simplified model, which aims to minimize the damped outrigger system cost, is proposed. A 600-m supertall building is presented as a case study. The accuracy and effectiveness of the simplified model and the optimal design method proposed in this study are illustrated. Thus, applying this optimal design method in combination with the simplified model can save significant analysis and design time and is conducive to the application of viscous damped outriggers in practical engineering.

Universal simplified spectral models and closed form solutions to the wind-induced responses for high-rise structures

High-rise structures are characterized as wind-sensitive vertical structures, estimating the wind-induced vibration response is a key to the structural design procedure. This study presented universal wind load spectral models for high-rise structures, including tri-para and κ model for along-wind load characterized by power dissipating with frequency and analog filter model for cross-wind load dominant by power concentration induced by vortex excitation. The spectral models appear to provide good agreement with wind tunnel data of buildings with various configurations. With analog filter approach, the along-wind spectra can be approximated by a linear filter polynomial and the cross-wind spectra is expressed by a quadratic filter polynomial. Thus forming a simple differential equation for the along- and cross-wind excitation based on a pseudo idea white noise. The closed form solutions to the wind-induced responses are derived based on analog filter approach. The Lyapunov equations are also provided in the state-space for high-rise structures with and without extra damping devices. The presented closed form solutions can provide a powerful tool in codification and vibration control optimization.

Toward A Mobile Robot for Vibration Control and Inspection of Power Lines

Abstract As power demand across communities increases, focus has been given to the maintenance of power lines against harsh environments such as wind-induced vibration (WIV). Inspection robots and fixed vibration absorbers (FVAs) are the current solutions. However, both solutions are currently facing many challenges. Inspection robots are limited by their size and considerable power demand, while FVAs are narrowband and unable to adapt to changing wind characteristics and thus are unable to reposition themselves at the antinodes of the vibrating loop. In view of these shortcomings, we propose a mobile damping robot (MDR) that integrates inspection robots mobility and FVAs WIV vibration control to help maintain power lines. In this effort, we model the conductor and the MDR by using Hamilton’s principle, and we consider the two-way nonlinear interaction between the MDR and the cable. The MDR is driven by a proportional-derivative (PD) controller to the optimal vibration location (antinodes) as the wind characteristics vary. The numerical simulations suggest that the MDR outperforms FVAs for vibration mitigation. Furthermore, the key parameters that influence the performance of the MDR are identified through a parametric study. The findings could setup a platform to design a prototype and experimentally evaluate the performance of the MDR.

A piezoelectric wind energy harvester excited indirectly by a coupler via magnetic-field coupling

Energy harvesting from wind-induced vibration energy using piezoelectric materials has received great attention because of the self-powered demand for wireless sensor networks. To improve the reliability, output performance and environmental adaptability (or designability of the structure), a piezoelectric wind energy harvester excited indirectly by a coupler via magnetic-field coupling (MC-PWEH) is proposed in this paper. The MC-PWEH is mainly composed of a piezoelectric transducer and a coupler consisting of a flexible beam, a cylinder, some exciting magnets and added coupler mass. By introducing the interaction of the piezoelectric transducer sealed in the chamber and the cylinder via the magnetic coupling, the interactive vortex-induced vibration (VIV) and galloping is realized and the composite vibration energy is transformed into electric energy. The feasibility of the structure and principle of the MC-PWEH is proved through theoretical simulations and experiments. The results indicated that the piezoelectric transducer began to oscillate strongly and generate fairly high output voltage when the wind speed exceeded a low critical wind speed, accompanied by a coupling phenomenon of VIV and galloping, and then finally converged to a stable value when the wind speed exceeded a high critical value. Moreover, the critical wind speeds, bandwidth of wind speed, natural frequency and power generation performance of the MC-PWEH could be adjusted by changing the structural parameters. Under the transducer proof mass of 50 g, the optimal wind speed bandwidth for the MC-PWEH to output voltage greater than 3.5 V obtained was 25.84 m⋅s−1 that occupies 86.12% of the experimental wind speed bandwidth. The achieved maximum output power was 4.73 mW at the optimal external load resistance of 1000 kΩ and wind speed of 24 m⋅s−1.

Parametric study on module wall-core system of concrete modular high-rises considering the influence of vertical inter-module connections

High-rise modular buildings are attractive for metropolises, but few applications exist. One reason is the lack of relevant knowledge about their lateral force resistance. Existing high-rise modular buildings generally adopt cast-in-situ concrete cores, which can work with precast module walls in concrete modular buildings to resist lateral loads together. This study aims to parametrically examine the module wall-core system. A typical 40-story public residential building in Hong Kong was selected as the case building and re-designed to be a concrete modular building. A method called generalized modulus reduction method was adopted to consider the influence of vertical grouted connections on lateral behavior of slender precast concrete walls. A three-dimensional finite element model using this method was established to study the influence of three parameters on the structural responses of the case building under the Hong Kong code-specified wind loads, which were the module wall thickness, the reduced lateral stiffness of module walls, and the defect distribution scenarios of vertical inter-module connections. Results show that the developed method can well consider the influence of vertical grouted connections. The module wall-core system can provide sufficient stiffness and strength for the case building, and module walls play a leading or even a major role. It is beneficial to increase the thickness of module walls due to reduced site work for core walls without adverse effects on the structural responses of buildings. With the reduced lateral stiffness of module walls, the case building’s deflection increases speedily, with more serious wind-induced vibration and more vulnerable core walls. When more defective vertical inter-module connections are concentrated on the bottom stories, there are relatively small impacts on overall structural responses of the case building, while strong adverse impacts on core walls at the corresponding bottom stories. For ensuring safer structural design, the influence of vertical inter-module connections on the global lateral force resistance of concrete modular high-rises cannot be ignored.