• Wind and Structures
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• v.17 no.1
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• pp.107-121
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• 2013

This paper presents an experimental investigation concerning the peak amplitudes of oscillation of a square prism due to Vortex-Induced-Vibrations (VIV) as a function of the mass damping parameter $m^*{\zeta}$(the so called Griffin--plot); $m^*$ and ${\zeta}$ being, respectively, the non-dimensional mass and the mechanical (structural) damping ratio. With this purpose in mind, an electromagnetic actuator has been employed to provide controlled damping. During the experiments the mass--damping parameter was in the range 0.15 < $m^*{\zeta}$ < 2.4. Experiments show that there is a value of $m^*{\zeta}$ below which VIV appears combined with galloping and the prism oscillation increases monotonically with the incoming flow velocity. For $m^*{\zeta}$ >0.3 the present experiments show a well-defined VIV phenomenon and, consequently, a Griffin-plot can be defined.

• Wind and Structures
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• v.16 no.4
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• pp.341-354
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• 2013

This paper presents an experimental investigation concerning the peak amplitudes of oscillation of a square prism due to Vortex-Induced-Vibrations (VIV) as a function of the mass damping parameter $m^*{\zeta}$ (the so called Griffin--plot); $m^*$ and ${\zeta}$ being, respectively, the non-dimensional mass and the mechanical (structural) damping ratio. With this purpose in mind, an electromagnetic actuator has been employed to provide controlled damping. During the experiments the mass--damping parameter was in the range 0.15 < $m^*{\zeta}$ < 2.4. Experiments show that there is a value of $m^*{\zeta}$ below which VIV appears combined with galloping and the prism oscillation increases monotonically with the incoming flow velocity. For $m^*{\zeta}$ >0.3 the present experiments show a well-defined VIV phenomenon and, consequently, a Griffin-plot can be defined.

• Wind and Structures
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• v.32 no.3
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• pp.179-191
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• 2021

A series of wind tunnel tests, including 1:50 sectional model tests, 1:50 free-standing bridge tower tests and 1:70 full-bridge aeroelastic model tests were carried out to systematically investigate the aerodynamic performance of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The test result indicates that there are three wind-resistant safety issues the HZMB encounters, including unacceptable low flutter critical wind speed, vertical vortex-induced vibration (VIV) of the main girder and galloping of the bridge tower in across-wind direction. Wind-induced vibration of HZMB can be effectively suppressed by the application of aerodynamic and mechanical measures. Acceptable flutter critical wind speed is achieved by optimizing the main girder form (before: large cantilever steel box girder, after: streamlined steel box girder) and cable type (before: central cable, after: double cable); The installations of wind fairing, guide plates and increasing structural damping are proved to be useful in suppressing the VIV of the HZMB; The galloping can be effectively suppressed by optimizing the interior angle on the windward side of the bridge tower. The present works provide scientific basis and guidance for wind resistance design of the HZMB.

• Journal of Korean Society of Steel Construction
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• v.13 no.3
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• pp.301-311
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• 2001

For a rectangular-highrise building with aspect ratio about six, the resonant wind speed of wind-induced vibration or galloping start wing speed can be within the design wind speed. The wind-induced vibration and galloping of highrise building with aspect ratio $H/\sqrt{DB}=6$, side ratio D/B=1 to 2 at intervals of 1/4 D/B were investigated in smooth flow. For the reducing effect of wind-induced vibration of highrise building, rectangular-highrise building with corners cutting about side ratio D/B=2 were investigated. Experimental results show that in the smooth flow non corners-cutting cases have tendency of increasing wind-induced vibration and galloping vibration then corner-cutting section. Therefore, the wind-induced vibrations on rectangular-highrise buildings were reduced effectively by using corner cut method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.303-305
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• 2014

This paper is concerned with the vibration measurement of cable by image processing technique. The measurement system consists of a CCD camera and zoom lens. The image data can be transferred to PC via USB or IEEE1394 port. In this study, a Matlab program was made to process the acquired image data. After acquiring an image data for each frame, this data is binarized for tracing cable vibrations. Then the area occupied by the cable is marked by 1 and the background is covered by 0. In this way, we can calculate the displacement of the cable. Experimental results show that the tracing of cable displacements is possible and natural frequencies and mode shapes can be computed. The accuracy of the image processing system for vibration measurement depends on the maximum frame rate of the CCD camera. The use of a high-speed camera enables us to compute more higher modes. The laboratory experiments guarantee the vibration measurement of real transmission lines.

• Wind and Structures
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• v.15 no.5
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• pp.385-407
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• 2012

Bridge hanger vibrations have been reported under icy conditions. In this paper, the results from a series of static and dynamic wind tunnel tests on a circular cylinder representing a bridge hanger with simulated thin ice accretions are presented. The experiments focus on ice accretions produced for wind perpendicular to the cylinder at velocities below 30 m/s and for temperatures between $-5^{\circ}C$ and $-1^{\circ}C$. Aerodynamic drag, lift and moment coefficients are obtained from the static tests, whilst mean and fluctuating responses are obtained from the dynamic tests. The influence of varying surface roughness is also examined. The static force coefficients are used to predict parameter regions where aerodynamic instability of the iced bridge hanger might be expected to occur, through use of an adapted theoretical 3-DOF quasi-steady galloping instability model, which accounts for sectional axial rotation. A comparison between the 3-DOF model and the instabilities found through two degree-of-freedom (2-DOF) dynamic tests is presented. It is shown that, although there is good agreement between the instabilities found through use of the quasi-steady theory and the dynamic tests, discrepancies exist-indicating the possible inability of quasi-steady theory to fully predict these vibrational instabilities.

• Wind and Structures
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• v.8 no.2
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• pp.107-120
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• 2005

The quasi-steady approaches to simulate the wind induced vibrations of inclined cables, especially on the rain-wind induced vibration, have been tried by many researchers. However, the steady wind force coefficients used in those methods include only the effects of water rivulet, but not the axial flow effects. The problem is the direct application of the conventional techniques to the inclined cable aerodynamics. Therefore, in this study, the method to implement the axial flow effects in the quasi-steady theory is considered and its applicability to the inclined cable aerodynamics is investigated. Then, it becomes clear that the perforated splitter plate in the wake of non-yawed circular cylinder can include the effects of axial flow in the steady wind force coefficients for inclined cables to a certain extent. Using the lateral force coefficients measured in this study, the quasi-steady theory may explain the wind induced instabilities of the inclined cables only in the relatively high reduced wind velocity region. When the Scruton number is less than around 40, the high speed vortex-induced vibration occurs around the onset wind velocity region of the galloping, and then, the quasi-steady approach cannot be applied for estimating the response of wind-induced vibration of inclined cable.

• Wind and Structures
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• v.30 no.6
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• pp.633-648
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• 2020

The objective of this work was to investigate the interference effects of two-parallel bridge decks on aerodynamic coefficients, vortex-induced vibration, flutter instability and flutter derivatives. The two bridges have significant difference in cross-sections, dynamic properties, and flutter speeds of each isolate bridge. The aerodynamic static tests and aeroelastic tests were performed in TU-AIT boundary layer wind tunnel in Thammasat University (Thailand) with sectional models in a 1:90 scale. Three configuration cases, including the new bridge stand-alone (case 1), the upstream new bridge and downstream existing bridge (case 2), and the downstream new bridge and the upstream existing bridge (case 3), were selected in this study. The covariance-driven stochastic subspace identification technique (SSI-COV) was applied to identify aerodynamic parameters (i.e., natural frequency, structural damping and state space matrix) of the decks. The results showed that, interference effects of two bridges decks on aerodynamic coefficients result in the slightly reduction of the drag coefficient of case 2 and 3 when compared with case 1. The two parallel configurations of the bridge result in vortex-induced vibrations (VIV) and significantly lower the flutter speed compared with the new bridge alone. The huge torsional motion from upstream new bridge (case 2) generated turbulent wakes flow and resulted in vertical aerodynamic damping H1^* of existing bridge becomes zero at wind speed of 72.01 m/s. In this case, the downstream existing bridge was subjected to galloping oscillation induced by the turbulent wake of upstream new bridge. The new bridge also results in significant reduction of the flutter speed of existing bridge from the 128.29 m/s flutter speed of the isolated existing bridge to the 75.35 m/s flutter speed of downstream existing bridge.