• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.6-15
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• 2008

This paper deals with the aeroelastic instability of vibrating multiple blade rows under aerodynamic coupling with each other. A model composed of three blade rows, e.g., rotor-stator-rotor, where blades of the two rotor cascades are simultaneously vibrating, is considered. The displacement of a blade vibrating under aerodynamic force is expanded in a modal series with the natural mode shape functions, and the modal amplitudes are treated as the generalized coordinates. The generalized mass matrix and the generalized stiffness matrix are formulated on the basis of the finite element concept. The generalized aerodynamic force on a vibrating blade consists of the component induced by the motion of the blade itself and those induced not only by vibrations of other blades of the same cascade but also vibrations of blades in another cascade. To evaluate the aerodynamic forces, the unsteady lifting surface theory for the model of three blade rows is applied. The so-called k method is applied to determine the critical flutter conditions. A numerical study has been conducted. The flutter boundaries are compared with those for a single blade row. It is shown that the effect of the aerodynamic blade row coupling substantially modifies the critical flutter conditions.

• Wind and Structures
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• v.36 no.4
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• pp.263-275
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• 2023

As a new kind of construction facility for high rise buildings, the integral steel platform scaffold system (ISPS) consisting of the steel skeleton and suspended scaffold faces high wind during the construction procedure. The lattice structure type and existence of core tubes both make it difficult to estimate the wind load and calculate the wind-induced responses. In this study, an aeroelastic model with a geometry scale ratio of 1:25 based on the ISPS for Shanghai Tower, with the representative square profile, is manufactured and then tested in a wind tunnel. The first mode of the prototype ISPS is a torsional one with a frequency of only 0.68 Hz, and the model survives under extreme wind speed up to 50 m/s. The static wind load and wind vibration factors are derived based on the test result and supplementary finite element analysis, offering a reference for the following ISPS design. The spacer at the bottom of the suspended scaffold is suggested to be long enough to touch the core tube in the initial status to prevent the collision. Besides, aerodynamic wind loads and cross-wind loads are suggested to be included in the structural design of the ISPS.

• Wind and Structures
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• v.37 no.5
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• pp.331-346
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• 2023

This work investigates the effects of transverse inclination on an aeroelastic prism through forced-vibration wind tunnel experiments. The aerodynamic characteristics are tri-parametrically evaluated under different wind speeds, inclination angles, and oscillation amplitudes. Results show that transverse inclination fundamentally changes the wake phenomenology by impinging the fix-end horseshoe vortex and breaking the separation symmetry. The aftermath is a bi-polar, one-and-for-all change in the aerodynamics near the prism base. The suppression of the horseshoe vortex unleashes the Kármán vortex, which significantly increases the unsteady crosswind force. After the initial morphology switch, the aerodynamics become independent of inclination angle and oscillation amplitude and depend solely on wind speed. The structure's upper portion does not feel the effect, so this phenomenon is called Base Intensification. The phenomenon only projects notable impacts on the low-speed and VIV regime and is indifferent in the high-speed. In practice, Base Intensification will disrupt the pedestrian-level wind environment from the unleashed Bérnard-Kármán vortex shedding. Moreover, it increases the aerodynamic load at a structure base by as much as 4.3 times. Since fix-end stiffness prevents elastic dissipation, the load translates to massive stress, making detection trickier and failures, if they are to occur, extreme, and without any warnings.

• Wind and Structures
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• v.35 no.4
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• pp.255-268
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• 2022

Light-weight or low-damped structures may encounter the unsteady galloping instability that occurs at low reduced wind speeds, where the classical quasi-steady assumption is invalid. Although this unsteady phenomenon has been widely studied for rectangular cross sections with one side perpendicular to the incidence flow, the effect of the mean wind angle of attack has not been paid enough attention yet. With four sectional models of different side ratios and geometric shapes, the presented research focuses on the effect of the wind angle of attack on unsteady galloping instability. In static tests, comparatively strong vortex shedding force was noticed in the middle of the range of flow incidence where the lift coefficient shows a negative slope. In aeroelastic tests with a low Scruton number, the typical unsteady galloping, which is due to an interaction with vortex-induced vibration and results in unrestricted oscillation initiating at the Kármán vortex resonance wind speed, was observed for the wind angles of attack that characterize relatively strong vortex shedding force. In contrast, for the wind angles of attack with relatively weak shedding force, an "atypical" unsteady galloping was found to occur at a reduced wind speed clearly higher than the Kármán-vortex resonance one. These observations are valid for all four wind tunnel models. One of the wind tunnel models (with a bridge deck cross section) was also tested in a turbulent flow with an intensity about 9%, showing only the atypical unsteady galloping. However, the wind angle of attack with the comparatively strong vortex shedding force remains the most unfavorable one with respect to the instability threshold in low Scruton number conditions.

• 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.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.147-160
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• 2007

In this paper, we described the aeroelastic full-bridge model tests that were conducted to investigate the effect of alternative temporary stabilizing measures for thecable-stayed bridge during construction to ensure aerodynamic stability in the event of a typhoon or similar disasters. The effect of alternative temporary stabilizing measures was investigated through various configurations on two cable-stayed bridges with a main span of 475 m and 230 m, respectively. To investigate the bridge's aerodynamic behaviour and dynamic wind force during construction, the deflections at the end of the cantilever, the accelerations atthe top of the pylon and the moments at the lower part of the pylon were measured. As the result, the system with two sets of vertical cables per cantilever seemed to be the overall most effective solution, but the system with single vertical cable may also work. The combined system using the caisson support and vertical cables and the system with two sets of inclined cables per cantilever on the same anchor block may also be a solution. The inclined cables from the caisson to the girder were effective for some early stages of erecting the deck.