• 제목/요약/키워드: Velocity Suppression

검색결과 106건 처리시간 0.027초

Mechanism on suppression in vortex-induced vibration of bridge deck with long projecting slab with countermeasures

  • Zhou, Zhiyong;Yang, Ting;Ding, Quanshun;Ge, Yaojun
    • Wind and Structures
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    • 제20권5호
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    • pp.643-660
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    • 2015
  • The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

Vibration Suppression Control for Mechanical Transfer Systems by Jerk Reduction

  • Hoshijima, Kohta;Ikeda, Masao
    • International Journal of Control, Automation, and Systems
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    • 제5권6호
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    • pp.614-620
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    • 2007
  • This paper considers vibration suppression of a mechanical transfer system, where the work is connected with the hand flexibly. We adopt the idea of jerk reduction of the hand. From the equation of motion, we first derive a state equation including the jerk and acceleration of the hand, but excluding the displacement and velocity of the work. Then, we design optimal state feedback for a suitable cost function, and show by simulation that jerk reduction of the hand is effective for vibration suppression of the work and improvement of the settling time. Since state feedback including the jerk and acceleration is not practical, we propose a computation method for optimal feedback using displacements and velocities in the state only.

유체유동에 의한 유연한 파이프의 불안정과 진동억제에 미치는 부가질량의 영향 (Effects of Attached Masses on the Instability and Vibration Suppression of a Flexible Pipe Conveying Fluid)

  • 류봉조;정승호;이종원
    • 소음진동
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    • 제10권2호
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    • pp.280-290
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    • 2000
  • The paper deals with vibration suppression and dynamic stability of a vertical cantilevered pipe conveying an internal flowing fluid and having an attached mass. Real pipe systems may have some valves or mechanical attached parts, which can be regarded as attached lumped masses. The effect of attached mass on the dynamic stability of a cantilevered pipe conveying fluid is investigated for different locations and magnitudes of the attached mass. The flow rate was controlled through motor pump output and measured by a flow meter. Experimental resutls in the vicinity of flutter fluid velocity were compared with theoretical predictions. It has been found that the experimental results are in substantial agreement with the theoretical predictions. Finally, in order to suppress the vibration of the pipe subjected to a disturbance, and control technique using an internal flowing fluid is introduced.

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컨테이너 크레인의 슬라이딩 모드제어 (Sliding-Mode Control of Container Cranes)

  • 이숙재;홍금식
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2004년도 추계학술대회 논문집
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    • pp.151-157
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    • 2004
  • In this paper, we propose a simple control scheme, based on second order sliding modes, which guarantees a fast and precise container transfer and the swing suppression during the container movement, despite of model uncertainties and unmodeled dynamic actuators. In the actual case, the swing suppression is obtained by constraining the system motion on a suitable surface which involves both the desired path and the swing angle. Strictly speaking, the trolley velocity is modified on-line, on the actual swing angle, to obtain the suppression of the oscillations not only at the end of the transport but during transfer as well. Such controller has been tested on a laboratory-size model of the 3Dcrane, and some experimental results are reported.

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미분무수 소화 노즐의 분무 특성 예측을 위한 CFD기법의 적용 (APPLICATION OF CFD TECHNIQUE TO PERFORMANCE PREDICTION OF SPRAY CHARACTERISTICS OF WATER-MIST FIRE SUPPRESSION NOZZLES)

  • 정희택;이창효;최병일;한용식;옥영욱
    • 한국전산유체공학회지
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    • 제11권4호
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    • pp.56-61
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    • 2006
  • Numerical simulation has been performed to investigate the characteristics of the mist flow through the fire suppression nozzles. The commercial CFD software, FLUENT with the proper modeling was applied for analyzing both the internal and external flow of the spray nozzles. Computations were made for the full cone nozzle in the operation range of the low pressure and high flow-rate. To validate the present computational procedure, numerical results are compared with measurements in terms of K-factor, SMD, axial spray velocity and spray angles. Numerical results suggested that the present numerical model can be used as an adequate tool for a design purpose of mist-spray nozzles.

지하 전력구내 OF 케이블의 화염전파속도 특성 실험 (Experiment on the Characteristics of Surface Flame Propagating Velocity of Oil filled Cable in the Underground Utility)

  • 이재하;정진용;홍기배;유홍선
    • 한국안전학회지
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    • 제20권2호
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    • pp.44-49
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    • 2005
  • Real-scale experimental study was performed to characterize the surface flame propagating velocity along the OF cable in the underground utility fire. Temperatures of oil filled OF cable and dried OF cable with the diameter of 90mn were measured using thermocouple and data log system. The hexane and alkyl-benzene oil were used as a fire source using the ignition device. As a result while the surface flame propagating velocity of the three cables was $0.06\~0.09cm/s$, the surface flame propagating velocity of the one cable was $0.028\~0.032cm/s$. Therefore, it was found that the surface propagating flame velocity of the three OF cables is $2.1\~2.8times$ faster than that of one OF cable case. The results show that the surface propagating flame velocity became larger as increase of the number of cable, the volume of alkyl-benzene oil in the cable. The characteristics of surface propagating flame velocity in the OF cable can be helpful to fire suppression system in utility.

Analysis and active control for wind induced vibration of beam with ACLD patch

  • Li, Jinqiang;Narita, Yoshihiro
    • Wind and Structures
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    • 제17권4호
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    • pp.399-417
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    • 2013
  • The structural vibration suppression with active constrained layer damping (ACLD) was widely studied recently. However, the literature seldom concerned with the vibration control on flow-induced vibration using active constrained layer. In this paper the wind induced vibration of cantilevered beam is analyzed and suppressed by using random theory together with a velocity feedback control strategy. The piezoelectric material and frequency dependent viscoelastic layer are used to achieve effective active damping in the vibration control. The transverse displacement and velocity in time and frequency domains, as well as the power spectral density and the mean-square value of the transverse displacement and velocity, are formulated under wind pressure at variable control gain. It is observed from the numerical results that the wind induced vibration can be significantly suppressed by using a small outside active voltage on the constrained layer.

Suppression of aerodynamic response of suspension bridges during erection and after completion by using tuned mass dampers

  • Boonyapinyo, Virote;Aksorn, Adul;Lukkunaprasit, Panitan
    • Wind and Structures
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    • 제10권1호
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    • pp.1-22
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    • 2007
  • The suppression of aerodynamic response of long-span suspension bridges during erection and after completion by using single TMD and multi TMD is presented in this paper. An advanced finite-element-based aerodynamic model that can be used to analyze both flutter instability and buffeting response in the time domain is also proposed. The frequency-dependent flutter derivatives are transferred into a time-dependent rational function, through which the coupling effects of three-dimensional aerodynamic motions under gusty winds can be accurately considered. The modal damping of a structure-TMD system is analyzed by the state-space approach. The numerical examples are performed on the Akashi Kaikyo Bridge with a main span of 1990 m. The bridge is idealized by a three-dimensional finite-element model consisting of 681 nodes. The results show that when the wind velocity is low, about 20 m/s, the multi TMD type 1 (the vertical and horizontal TMD with 1% mass ratio in each direction together with the torsional TMD with ratio of 1% mass moment of inertia) can significantly reduce the buffeting response in vertical, horizontal and torsional directions by 8.6-13%. When the wind velocity increases to 40 m/s, the control efficiency of a multi TMD in reducing the torsional buffeting response increases greatly to 28%. However, its control efficiency in the vertical and horizontal directions reduces. The results also indicate that the critical wind velocity for flutter instability during erection is significantly lower than that of the completed bridge. By pylon-to-midspan configuration, the minimum critical wind velocity of 57.70 m/s occurs at stage of 85% deck completion.

Internal Flow Characteristics in the Draft Tube of a Francis Turbine

  • Wei, Qingsheng;Zhu, Baoshan;Choi, Young-Do
    • Journal of Advanced Marine Engineering and Technology
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    • 제36권5호
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    • pp.618-626
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    • 2012
  • Suppression of abnormal flow phenomena in the Francis hydro turbine is very important to improve the turbine performance. Especially, as cavitation and cavitation surge makes serious problems when the turbine is operated in the range of partial flow rate, optimum method of suppressing the abnormal flow characteristics is required necessarily. Moreover, as swirl flow in the draft tube of the Francis turbine decreases pressure at the inlet of the draft tube, suppression of the swirl flow can be an useful method of suppressing the occurrence of cavitation. In order to clarifying the possibility of suppressing the swirl flow by J-Groove in the draft tube, a series of CFD analysis has been conducted in the range of partial load, designed condition and excessive flow rate of a Francis turbine. A kind of J-Groove is designed and applied to the draft tube of the Francis hydro turbine model. The pressure contours, circumferential velocity vectors and vortex core regions in the draft tube are compared by the conditions with or without J-Groove. In addition, a group of data about the velocity in the draft is presented to show the influence of J-Groove.

A-mode 불안정성 영역에서 교란유동장에 놓인 원형실린더 후류의 천이지연과 유동공진의 발생 (Suppression of Wake Transition and Occurrence of Lock-on Downstream of a Circular Cylinder in a Perturbed Flow in the A-mode Instability Regime)

  • 김수현;배종헌;유정열
    • 대한기계학회논문집B
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    • 제31권8호
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    • pp.702-710
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    • 2007
  • Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.