• Wind and Structures
• /
• v.7 no.1
• /
• pp.41-54
• /
• 2004

An analysis refinement of the Messina Strait suspension bridge project has been recently required, concerning mainly the yaw angle effects on the multi-box deck section aerodynamics and the vortex shedding at low reduced velocities $V^*$. In particular the possible interaction of the axial flow with the large cross beams has been investigated. An original test rig has been designed at this purpose allowing for both forced motion and free motion aero elastic tests, varying the average angle of attack ${\alpha}$ and the deck yaw angle ${\beta}$. The hydraulic driven test rig allowed for both dynamic and stationary tests so that both the stationary coefficients and the flutter derivatives have been evaluated for each yaw angle. Specific free motion tests, taking advantage from the aeroelastic features of the section model, allowed also the study of the vortex shedding induced phenomena.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.6
• /
• pp.92-100
• /
• 2002

In this study, transonic/supersonic nonlinear flutter analysis system of a complete aircraft including forced harmonic motion pf control surfaces has been effectively developed using the modified transonic small disturbance (TSD) equation. To consider the nonlinear effects, the coupled time marching method (CTM) combining computational structural dynamics (CFD) has been directly applied for aeroelastic computations. The grid system for a complex full aircraft configuration is effectively generated by the developed inhouse code. Intransonic and supersonic flight regimes, the characteristics of static and dynamic aeroelastic effect has been investigated for a complete aircraft model. Also, nonlinear flutter flight simulations for the forced harmonic motion of control surfaces are practically presented in detail.

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

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.7 s.100
• /
• pp.813-820
• /
• 2005

A deployable missile control fin has some structural nonlinearities because of the worn or loose hinges and the manufacturing tolerance. The structural nonlinearity cannot be eliminated completely, and exerts significant effects on the static and dynamic characteristics of the control fin. Thus, It is important to establish the accurate deployable missile control fin model. In the present study, the nonlinear dynamic model of 4he deployable missile control fin is developed using a substructure synthesis method. The deployable missile control fin can be subdivided Into two substructures represented by linear dynamic models and a nonlinear hinge with structural nonlinearities. The nonlinear hinge model is established by using a system identification method, and the substructure modes are improved using the Frequency Response Method. A substructure synthesis method Is expanded to couple the substructure models and the nonlinear hinge model, and the nonlinear dynamic model of the fin is developed. Finally, the established nonlinear dynamic model of the deployable missile control fin is verified by dynamic tests. The established model is In good agreement with test results, showing that the present approach is useful in aeroelastic stability analyses such as time-domain nonlinear flutter analysis.

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

• Structural Engineering and Mechanics
• /
• v.75 no.4
• /
• pp.487-496
• /
• 2020

Most of the previous works on numerical analysis of galloping of transmission lines are generally based on the quasisteady theory. However, some wind tunnel tests of the rectangular section or hangers of suspension bridges have shown that the galloping phenomenon has a strong unsteady characteristic and the test results are quite different from the quasi-steady calculation results. Therefore, it is necessary to check the applicability of the quasi-static theory in galloping analysis of the ice-covered transmission line. Although some limited unsteady simulation researches have been conducted on the variation of parameters such as aerodynamic damping, aerodynamic coefficients with wind speed or wind attack angle, there is a need to investigate the numerical simulation of unsteady galloping of two-dimensional iced transmission line with comparison to wind tunnel test results. In this paper, it is proposed to conduct a two dimensional (2-D) unsteady numerical analysis of ice-covered transmission line galloping. First, wind tunnel tests of a typical crescent-shapes iced conductor are conducted firstly to check the subsequent quasisteady and unsteady numerical analysis results. Then, a numerical simulation model consistent with the aeroelastic model in the wind tunnel test is established. The weak coupling methodology is used to consider the fluid-structure interaction in investigating a two-dimension numerical simulation of unsteady galloping of the iced conductor. First, the flow field is simulated to obtain the pressure and velocity distribution of the flow field. The fluid action on the iced conduct at the coupling interface is treated as an external load to the conductor. Then, the movement of the conduct is analyzed separately. The software ANSYS FLUENT is employed and redeveloped to numerically analyze the model responses based on fluid-structure interaction theory. The numerical simulation results of unsteady galloping of the iced conduct are compared with the measured responses of wind tunnel tests and the numerical results by the conventional quasi-steady theory, respectively.

• Journal of Korean Society of Steel Construction
• /
• v.9 no.2 s.31
• /
• pp.259-267
• /
• 1997

Wind tunnel test results and their interpretations focused on the behavior of girder, which were performed to study the aerodynamic stability of a self-anchored suspension bridge with lateral sag of main cable, are presented in this paper The shape of the girder which has the best aerodynamic stability was selected based on the section model test under uniform and turbulent flow conditions. Good performance of the selected section was confirmed in the full bridge model test. Measured flutter derivatives are presented for further study. Buffeting response was investigated to check the fatigue problem and serviceability of the bridge but it was found to be acceptable from the engineering point of view. Even though the drag coefficient of the girder had high value, the amplitude of the lateral vibration was found to be very low. This may be due to the restraint provided by the lateral sag of the cables.

• Wind and Structures
• /
• v.27 no.5
• /
• pp.293-309
• /
• 2018

The prediction of multimode flutter relies, to a larger extent than bimodal flutter, on accurate modeling of the self-excited forces since it is challenging to perform experimental validation by using aeroelastic tests for a multimode case. This paper sheds some light on the accuracy of predicted self-excited forces by comparing numerical predictions of self-excited forces with measured forces from wind tunnel tests considering the flutter vibration mode. The critical velocity and the corresponding flutter vibration mode of the Hardanger Bridge are first determined using the classical multimode approach. Then, a section model of the bridge is forced to undergo a motion corresponding to the flutter vibration mode at selected points along the bridge, during which the forces that act upon it are measured. The measured self-excited forces are compared with numerical predictions to assess the uncertainty involved in the modeling. The self-excited lift and pitching moment are captured in an excellent manner by the aerodynamic derivatives. The self-excited drag force is, on the other hand, not well represented since second-order effects dominate. However, the self-excited drag force is very small for the cross-section considered, making its influence on the critical velocity marginal. The self-excited drag force can, however, be of higher importance for other cross-sections.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.2
• /
• pp.99-105
• /
• 2017

Wind tunnel test which is one of the method to predict the aeroelastic characteristics has difficulties to make scale-down structural model and achieve a specified free stream velocity. It is very costly and complicated to consider similarity relationships between real structure and scale-down structural model. "Dry Wind-Tunnel(DWT)" was proposed to overcome these difficulties. This is made up of Ground Vibration Test hardware and software to compute the aerodynamic forces. In the present study, program for computing the real-time unsteady aerodynamic forces which is an important part of DWT system was developed by Matlab Simulink and dSPACE. In addition, using this program and software which is a part of the test structure, a real-time flutter analysis was conducted and the results are verified by ZAERO.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.37 no.1
• /
• pp.9-17
• /
• 2017

Characteristics of aerodynamic damping ratios of a helical $180^{\circ}$ model which shows better aerodynamic behavior in both along-wind and across-wind responses on a super tall building was investigated by an aeroelastic model test. The aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement (RD) technique. Further, various triggering levels in evaluation of aerodynamic damping ratios using RD technique were also examined. As a result, it was found that when at least 2000 segments were used for evaluating aerodynamic damping ratio for ensemble averaging, the aerodynamic damping ratio can be obtained more consistently with lower irregular fluctuations. This is good agreement with those of previous studies. Another notable observation was that for square and helical $180^{\circ}$ models, the aerodynamic damping ratios in along-wind direction showed similar linear trends with reduced wind speeds regarding of building shapes. On the other hand, for the helical $180^{\circ}$ model, the aerodynamic damping ratio in across-wind direction showed quite different trends with those of the square model. In addition, the aerodynamic damping ratios of the helical $180^{\circ}$ model showed very similar trends with respect to the change of wind direction, and showed gradually increasing trends having small fluctuations with reduced wind speeds. Another observation was that in definition of triggering levels in RD technique on aerodynamic damping ratios, it may be possible to adopt the triggering levels of "standard deviation" or "${\sqrt{2}}$ times of the standard deviation" of the response time history if RD functions have a large number of triggering points. Further, these triggering levels may result in similar values and distributions with reduced wind speeds and either may be acceptable.