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  1. This paper reviews the state-of-the-art and –practice on various methodologies developed to control the wind-induced vibration of tall buildings. Tall buildings experience wind-induced vibration in the along- and across-wind directions depending on the wind direction, building shape, height, and structural properties. It is possible to control the wind response of buildings through passive, active, and semi-active systems. Damping systems, which are widely used to reduce the structural vibrations, are reviewed, and their performance in alleviating the building vibration is discussed. It was found that the application of conventional dampers needs to be reassessed to ensure their efficiency in dissipating the energy, especially caused by wind loads. Specific attention has been given to the aerodynamic modification of building shapes considering their effectiveness and high popularity within the wind engineering community. A comprehensive review of the existing wind tunnel experiment and Computational Fluid Dynamics (CFD) studies are conducted here to present the past and recent achievements on the response mitigation of tall buildings. A comparative study on the performance of different systems has been provided that can provide a commencing point for future studies. The existing challenges and their solutions are explained, and suggestions for future studies are proposed. It is expectedmore »that the information provided in this paper will facilitate further research in the area of wind-induced vibration mitigation approaches of tall buildings.« less
  2. This paper presents a quasi-steady technique that combines aerodynamic force coefficients from straight-line wind tunnel tests with empirically developed tornado wind speed profiles to estimate the time history of aerodynamic loads on lattice structures. The methodology is specifically useful for large and geometrically complex structures that could not be modeled with reasonable scales in the limited number of tornado simulation facilities across the world. For this purpose, the experimentally developed tornado wind speed profiles were extracted from a laboratory tornado wind field and aerodynamic force coefficients of different segments of a lattice tower structure were assessed for various wind directions in a wind tunnel. The proposed method was then used to calculate the wind forces in the time domain on the model lattice tower for different orientation angles with respect to the tornado’s mean path based on the empirical tornado wind speed profiles and the measured aerodynamic force coefficient of each tower segment, where the wind field at the tower location was updated at each time step as the tornado went past the tower. A tornado laboratory simulation test was conducted to measure the wind loads on a scaled model of a lattice tower subject to a translating tornado formore »the purpose of validation of the proposed method. The moving average of the horizontal wind force on the lattice tower model that was calculated with this method compared very well with that measured in a laboratory tornado simulator, which paves the way for the use of straight-line wind tunnels to assess tornado-induced loads on a lattice structure and possibly other similar structures.« less
  3. Wake-induced aerodynamics of yawed circular cylinders with smooth and grooved surfaces in a tandem arrangement was studied. This pair of cylinders represent sections of stay-cables with smooth surfaces and high-voltage power conductors with grooved surfaces that are vulnerable to flow-induced structural failure. The study provides some insight for a better understanding of wake-induced loads and galloping problem of bundled cables. All experiments in this study were conducted using a pair of stationary section models of circular cylinders in a wind tunnel subjected to uniform and smooth flow. The aerodynamic force coefficients and vortex-shedding frequency of the downstream model were extracted from the surface pressure distribution. For measurement, polished aluminum tubes were used as smooth cables; and hollow tubes with a helically grooved surface were used as power conductors. The aerodynamic properties of the downstream model were captured at wind speeds of about 6-23 m/s (Reynolds number of 5×10^4 to 2.67×10^5 for smooth cable and 2×10^4 to 1.01×10^5 for grooved cable) and yaw angles ranging from 0º to 45º while the upstream model was fixed at various spacing between the two model cylinders. The results showed that the Strouhal number of yawed cable is less than the non-yawed case at amore »given Reynolds number, and its value is smaller than the Strouhal number of a single cable. Additionally, compared to the single smooth cable, it was observed that there was a reduction of drag coefficient of the downstream model, but no change in a drag coefficient of the downstream grooved case in the range of Reynolds number in this study.« less
  4. Inclined cables used in bridges or other infrastructures are vulnerable to unsteady wind-induced loads producing moderate- to large-amplitude vibration that may result in damage or failure of the cables, resulting in catastrophic failure of the structure they secure. In the present study, wind-induced response of an inclined smooth cable was studied through wind tunnel measurements using a flexible cable model for a better understanding of the vibration characteristics of structural cables in atmospheric boundary layer wind. For this purpose, in-plane and out-of-plane responses of a sagged and a non-sagged flexible cable were recorded by four accelerometers. Four cases with different yaw and inclination angles of a cable with approximate sag ratios of 1/10 were studied to investigate the wind directionality effect on its excitation mode(s) and response amplitude. Cable tension was also measured during all experiments to assess the correlation of wind speed, excitation vibration mode, and natural frequency of the cable with change in cable tension. Additionally, two inclined cables with no sag were tested to determine the influence of sag of a cable on its vibration characteristics. In the second part of this study, a series of finite element analyses were conducted to predict the wind-induced aerodynamic dampingmore »of an inclined bridge cable. Experimental results showed that excitation mode(s) of a cable depend on wind speed, inclination angle, and sag ratio and cable tension. First, second, and third vibration modes were observed at a low wind speed for different test cases, whereas higher vibration modes were observed to contribute to the cable response at high wind speeds. Moreover, it was seen that the cable tension significantly increased with wind speed resulting in increased value of the excited natural frequency. Numerical results obtained through finite element analysis of an inclined full-scale cable showed that the criteria that are based on section models can underestimate the critical reduced velocity for dry cable galloping.« less
  5. 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 unsteadymore »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.« less
  6. Cables of suspension, cable-stayed and tied-arch bridges, suspended roofs, and power transmission lines are prone to moderate to large-amplitude vibrations in wind because of their low inherent damping. Structural or fatigue failure of a cable, due to these vibrations, pose a significant threat to the safety and serviceability of these structures. Over the past few decades, many studies have investigated the mechanisms that cause different types of flow-induced vibrations in cables such as rain-wind induced vibration (RWIV), vortex-induced vibration (VIV), iced cable galloping, wake galloping, and dry-cable galloping that have resulted in an improved understanding of the cause of these vibrations. In this study, the parameters governing the turbulence-induced (buffeting) and motion-induced wind loads (self-excited) for inclined and yawed dry cables have been identified. These parameters facilitate the prediction of their response in turbulent wind and estimate the incipient condition for onset of dry-cable galloping. Wind tunnel experiments were performed to measure the parameters governing the aerodynamic and aeroelastic forces on a yawed dry cable. This study mainly focuses on the prediction of critical reduced velocity 〖(RV〗_cr) as a function of equivalent yaw angle (*) and Scruton number (Sc) through measurement of aerodynamic- damping and stiffness. Wind tunnel tests usingmore »a section model of a smooth cable were performed under uniform and smooth/gusty flow conditions in the AABL Wind and Gust Tunnel located at Iowa State University. Static model tests for equivalent yaw angles of 0º to 45º indicate that the mean drag coefficient 〖(C〗_D) and Strouhal number (St) of a yawed cable decreases with the yaw angle, while the mean lift coefficient 〖(C〗_L) remains zero in the subcritical Reynolds number (Re) regime. Dynamic one degree-of-freedom model tests in across-wind and along-wind directions resulted in the identification of buffeting indicial derivative functions and flutter derivatives of a yawed cable for a range of equivalent yaw angles. Empirical equations for mean drag coefficient, Strouhal number, buffeting indicial derivative functions and critical reduced velocity for dry-cable galloping are proposed for yawed cables. The results indicate a critical equivalent yaw angle of 45° for dry-cable galloping. A simplified design procedure is introduced to estimate the minimum damping required to arrest dry-cable galloping from occurring below the design wind speed of the cable structure. Furthermore, the results from this study can be applied to predict the wind load and response of a dry cable at a specified wind speed for a given yaw angle.« less