• Title/Summary/Keyword: Aerodynamic damping

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An Experimental Study on Roll-Damping Characteristics of a Finned Spinning Projectile (회전발사체 미익형상 롤댐핑 특성에 관한 실험연구)

  • Oh, Se-Yoon;Lee, Do-Kwan;Kim, Sung-Cheol;Kim, Sang-Ho;Ahn, Seung-Ki
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.10
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    • pp.894-900
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    • 2012
  • The purpose of this research is to investigate the dynamic roll-damping characteristics of a spin-stabilized projectile in wind-tunnel testing. In the present work, the high-speed wind-tunnel tests for the roll-damping measurements were conducted on a finned spin-stabilized projectile model in the Agency for Defense Development's Trisonic Wind Tunnel at spin rates about 8,000 rpm. The test Mach numbers ranged from 0.6 to 0.9, and the angles of attack ranged from 0 to +15 deg. The evaluation of the bearing friction parameter was also conducted to eliminate the tare damping moment from the aerodynamic damping moment.

Dynamic Characteristics Research of DVD Disk due to Disk-Wall Gap (간격 변화에 따른 DVD 디스크의 동특성 연구)

  • 임효석;이승엽
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.11a
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    • pp.1095-1100
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    • 2003
  • Experimental studies on the aerodynamic coupling effect on natural frequencies, critical speed and flutter instability of DVD disks are investigated in this paper. The experimental results are compared with the theoretical analyses where the aerodynamic effects are represented in terms of elastic, lift and damping and stiffness components. The experiments are performed using a vacuum chamber and DVD disks rotating in vacuum, open and enclosure with several different gaps between disk and wall. The following three results are given. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency decreases as the disk-wall gap is decreased. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

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Experimental analysis of aerodynamic stability of stress-ribbon footbridges

  • Pirner, Miros;Fischer, Ondrej
    • Wind and Structures
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    • v.2 no.2
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    • pp.95-104
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    • 1999
  • The dynamic properties of one-span or multi-span reinforced concrete footbridges of catenary form (see e.g., Fig. 1) include the very low fundamental natural frequency, usually near the step-frequency of pedestrians, and the low damping of bending vibrations. The paper summarized the results of model as well as full-scale measurements with particular reference to the influence of torsional rigidity of the stress-ribbon on the magnitude of aerodynamic response, the results of measurements on footbridges of catenary form being completed by results obtained on footbridges of some other types. Additionally the influence of the local broadening of the bridge deck on the bridge response was tested. Starting from these results the criterion has been derived for the decision, whether the flutter analysis is necessary for the design of the footbridge.

Vibration Characteristics of CD and DVD Disks (CD 및 DVD 디스크의 진동 특성)

  • 이승엽;임효석
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2003.05a
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    • pp.998-1003
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    • 2003
  • The aerodynamically excited vibration and natural frequency of rotating CD and DVD disks are analytically and experimentally studied in this paper The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping components. The explicit expression on natural frequency of the air coupled disk is obtained as functions of the three aerodynamic coefficients. The experiments performed using a vacuum chamber and CD/DVD disks rotating in vacuum, open air and enclosure give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

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Wind-induced response and loads for the Confederation Bridge -Part II: derivation of wind loads

  • Bakht, Bilal;King, J. Peter C.;Bartlett, F.M.
    • Wind and Structures
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    • v.16 no.4
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    • pp.393-409
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    • 2013
  • This paper uses ten years of on-site monitoring data for the Confederation Bridge to derive wind loads and investigate whether the bridge has experienced its design wind force effects since its completion in 1997. The load effects derived using loads from the on-site monitoring data are compared to the load effects derived using loads from the 1994 and 2009 wind tunnel aerodynamic model tests. The research shows, for the first time, that the aerodynamic model-based methodology originally developed in 1994 is a very accurate method for deriving wind loads for structural design. The research also confirms that the bridge has not experienced its specified (i.e., unfactored) wind force effects since it was opened to traffic in 1997, even during the most severe event that has occurred during this period.

Numerical Analysis on Transient Response of Turbine Blandes by Partial Admission (부분 유입되는 터빈 블레이드의 과도 응답 특성에 대한 수치 해석)

  • 이진갑
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.3
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    • pp.396-404
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    • 1998
  • A numerical analysis is presented for the transient behavior of a rotating turbines blades. The response due to partial admission during start-up and resonance pass is considered, Modal analysis and numerical integation method are used for solving the problems A theory for determining the material and aerodynamic damping values of turbine blades is presented. The damping values of the various modeling of blaes-uniform beam and tapered twisted beam-are calculated and the influence on blades response is investigated. The effect of angular velocity on transient response are also shown.

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Ground effects on wind-induced responses of a closed box girder

  • Mao, Wenhao;Zhou, Zhiyong
    • Wind and Structures
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    • v.25 no.4
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    • pp.397-413
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    • 2017
  • When bridges are constructed with lower heights from the ground, the formed channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to "ground effects." So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been performed. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number ($S_t$), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability.

Aerodynamic stability of iced stay cables on cable-stayed bridge

  • Li, Shouying;Wu, Teng;Huang, Tao;Chen, Zhengqing
    • Wind and Structures
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    • v.23 no.3
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    • pp.253-273
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    • 2016
  • Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

A Study on Buffeting Responses of a In-service Steel Cable-stayed Bridge Using Full-scale Measurements (실측 데이터를 이용한 공용중인 강사장교의 버페팅 응답 분석)

  • Lee, Deok Keun;Kong, Min Joon;You, Dong Woo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.36 no.3
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    • pp.349-359
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    • 2016
  • In order to analytically evaluate buffeting responses, the analysis of wind characteristics such as turbulence intensity, turbulence length, gust, roughness coefficient, etc must be a priority. Static aerodynamic force coefficients, flutter coefficients, structural damping ratios, aerodynamic damping ratios and natural frequencies affect the analytical responses. The bridge interested in this paper has being been used for 32 years. As the time passes, current terrain conditions around the bridge are different markedly from the conditions it was built 32 years ago. Also, wind environments were considerably varied by the climate change. For this reason, it is necessary to evaluate the turbulence intensity, length, spectrum and roughness coefficient of the bridge site from full-scale measurements using the structural health monitoring system. The evaluation results indicate that wind characteristics of bridge site is analogous to that of open terrain although the bridge is located on the coastal area. To calculate buffeting responses, the analysis variables such as damping ratios, static aerodynamic force coefficients and natural frequency were evaluated from measured data. The analysis was performed with regard to 4 cases. The evaluated variables from measured data are applied to the first and second analysis cases. And the other analysis cases were performed based on Design Guidelines for Steel Cable Supported Bridges. The calculated responses of each analysis cases are compared with the buffeting response measured at less than 25m/s wind speed. It is verified that the responses by the numerical analysis applying the estimated variables based on full-scale measurements are well agreed with the measured actual buffeting responses under wind speed 25m/s. Also, the extreme wind speed corresponding to a recurrence interval 200 years is derived from Gumbel distribution. The derived wind speed for return period of 200 years is 45m/s. Therefore the buffeting responses at wind speed 45m/s is determined by the analysis applying the estimated variables.

A Study on Estimation of Energy required for Fin Unfolding (공력면 전개에 필요한 전개 에너지의 추산에 관한 연구)

  • Jung, Suk-Young
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.3
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    • pp.283-292
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    • 2009
  • Considering an integral equation governing the motion of unfolding fin, an algebraic equation was acquired to get estimated minimum deployment energy required for the successful fin unfolding under the given wind condition. To complete the integration of moment, some approximations had to be introduced particularly to frictional moment and aerodynamic damping for which deployment angular speed of the unfolding fin was modelled as a function of deployment angle only with assumed profile using expected maximum angular speed. Technique for the estimation of the minimum required deployment energy was finalized by introducing the ideal deployment angular speed representing work done by the fin unfolding device alone during fin unfolding and was confirmed by comparing results from simulation with various aerodynamic conditions and profiles of the hinge torque.