• Title/Summary/Keyword: 수치풍동

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Evaluation of Flutter Velocity of Bridge Deck Section using Distributed Computing Environment (분산형 전산환경을 활용한 교량 거더의 플러터 발생풍속 산정)

  • Lee, Kuen-Bae;Kim, Chongam
    • 한국방재학회:학술대회논문집
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    • 2011.02a
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    • pp.75-75
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    • 2011
  • 본 논문에서는 진동중인 교량 거더에 작용하는 풍하중을 산정하고 그에 따른 플러터 발생풍속을 예측하기 위하여 분산형 전산환경을 활용한 수치해석 연구를 수행하였다. 분산형 전산환경은 웹 포탈을 기반으로 수치해석 환경을 제공하는 수치풍동 시스템으로서, 전산유체역학(CFD : Computational Fluid Dynamics)에 대한 전문지식이 부족한 사용자들도 격자생성, 수치해석자를 이용한 계산, 가시화 등의 전 과정을 편리하게 수행할 수 있는 차세대 토목분야 연구 환경이다. 본 시스템은 그리드스피어(GfidSphere)를 기반으로 구성되었으며, 기본적으로 사용자 관리, 세션 관리, 그룹 관리, 레이아웃 관리 등을 제공하여 사용자가 포탈을 통해서 다양한 서비스를 쉽게 사용할 수 있는 환경을 구축하도록 도와준다. 수치해석을 위한 유체 지배방정식은 2차원 비정상 비압축성 RANS(Reynolds-Averaged Navier-Stokes) 방정식이며, pseudo compressibility 방법을 적용하였다. 비정상 유동장을 해석하기 위하여 이중시간 전진법(dual time stepping)을 사용하였으며, 수렴가속화를 위해 Multi-grid 기법을 적용하였다. 또한 난류 유동장 해석을 위해서 $k-{\omega}$ SST 난류 모델을 사용하였으며, 난류 천이 과정에서의 유동을 모사하기 위하여 Total stress limitation 방법을 적용하였다. 교량 거더의 연직과 회전방향의 2자유도 움직임을 모사하기 위하여 동적격자 기법을 도입하였다. 교량 거더 주변의 비정상 유동해석 결과를 통해, 거더 표면에서 떨어져나가는 크고 작은 와류의 영향으로 양력 및 모멘트 계수 그래프가 중첩된 진폭과 주기를 갖고 주기적으로 나타나는 것을 확인할 수 있었다. 또한 계산된 비정상 공기력을 적용한 2자유도 플러터 방정식을 통하여 플러터 발생풍속을 산정하였다. 최종적으로 본 연구에서 계산된 결과의 타당성을 검증하기 위하여 수치적으로 구한 플러터 발생풍속과 기존의 실험 및 수치해석 결과를 비교하였으며, 결과는 잘 일치하였다.

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A Study on the Flow Characteristics in the Upstream- and Downstream-Diaphragm Ludwieg Tubes (상류막 방식과 하류막 방식의 Ludwieg Tube에서 발생하는 유동특성에 관한 연구)

  • Shin, Choon-Sik;Kim, Heuy-Dong
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.11a
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    • pp.363-366
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    • 2010
  • Among the many different types of wind tunnels, Ludwieg Tube(LT) is the most suitable facility for high Reynolds number testing. Depending on the location of diaphragm, there are two types of LTs. In the present study, a computational work has been carried out to compare the operation characteristics of upstream- and downstream-diaphragm LTs. Two-dimensional, axisymmetric, unsteady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. Based on the present results, the flow mechanism of the starting process was discussed in detail using wave diagrams and characteristics of starting time and working time were investigated.

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An Unsteady Numerical Method of Autorotation and the Effect of 2D Aerodynamic Coefficients (자동회전의 비정상 수치해법과 2차원 공력계수의 영향)

  • Kim, Hak-Yoon;Sheen, Dong-Jin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.2
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    • pp.121-130
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    • 2009
  • An unsteady numerical simulation method for an autorotating rotor in forward flight was developed. The flapping and rotational equations of motion of autorotation are continuously integrated for given time steps, meanwhile the induced velocity field at disc plane is obtained by the dynamic inflow theory embodying the unteadiness. The transitions from arbitrary initial states to equilibrium states were simulated. Steady autorotations as numerical solutions of equations were predicted by using two sources of blade airfoil data. The simulations using airfoil data which were obtained by a two dimensional Navier-Stokes solver in terms of angles of attack and Reynolds numbers have shown good agreements with wind tunnel experimental results.

Combustion Characteristics of Hypersonic SCRamjet Engine (극초음속 스크램제트 엔진의 연소특성)

  • 원수희;정은주;정인석;최정열
    • Journal of the Korean Society of Propulsion Engineers
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    • v.8 no.1
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    • pp.61-69
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    • 2004
  • This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of model SCRamjet engine combustor, where a hydrogen jet injected into a supersonic cross flow and in a cavity Combustion phenomena in a model SCRamjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, was observed around separation region of upstream of the normal injector and inside of cavity. The results show that the separation region and cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs in the separation-freestream and cavity-freestream interface.

A Study of Aerodynamic Modelling for Fin Unfolding Motion Analysis (공력면 전개 모사를 위한 공력 모델링 연구)

  • Jung, Suk-Young;Yoon, Sung-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.5
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    • pp.420-427
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    • 2008
  • For simulation of a fin unfolding motion for the various aerodynamic conditions, equations and moments applying to the unfolding fin were modelled. Aerodynamic roll moment consists of the static roll moment and the damping moment, which were obtained through wind tunnel tests and numerical analyses respectively. Panel method was used to compute the roll damping coefficient with deflected fin, whose angle was equivalent to angle of attack due to the deployment motion. Roll damping coefficient is a function of angle of attack, sideslip angle, and deployment angle but not of angular velocity of deployment. Simulation with aerodynamic damping model gave more similar deployment time compared to fin deployment test results.

A Study of Computation Methods for Dynamic Damping Coefficients of an Airship (비행선의 동적 감쇠계수 계산 방법에 관한 연구)

  • Park, Su Hyeong;Jang, Byeong Hui;Kim, Yu Jin;Gwon, Jang Hyeok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.5
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    • pp.10-17
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    • 2003
  • Dynamic stability is critically required to stabilize an airship which is statically unstable. Numerical computations were performed in order to support and confirm the foced oscillation wind tunnel tests. To analyze the low-speed flow filed around the airship, a low-Mach number preconditioned method was applied. Using two computation methods, variations of the dynamic damping coefficients were examined. Numerical results show that it is dynamically stable for three directional moments, but unstable for normal or side force. It is revealed that the damping coefficients are more sensitive to the direction of the angular rate than the angle of attack or the magnitude og angular rate.

Application of CFD in The Analysis of Aerodynamic Characteristics for Aircraft Propellers (전산유체역학을 이용한 항공기 프로펠러 공력특성 연구)

  • Cho, Kyuchul;Kim, Hyojin;Park, Il-Ju;Jang, Sungbok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.11
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    • pp.917-926
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    • 2012
  • The analysis of aerodynamic characteristics for aircraft propellers is studied to develop high efficiency composite propellers. It is to verify the accuracy and reliability of predicting the efficiency characteristics of aircraft propellers by applying nonlinear numerical analysis. The numerical simulation method incorporated the CFD code, which is based on RANS (Reynolds Averaged Navier-Stocks) equation. The study includes a comparative analysis between the numerical simulation results and the wind tunnel test results of the full-scale aircraft propeller. The comparison shows that thrust and power coefficients of the propeller calculated by nonlinear numerical analysis are higher than those based on the results generated from the wind tunnel test. The efficiency of the propeller calculated by numerical analysis matches closely to the efficiency based on the wind tunnel test results. The verification results are analyzed, then, will be used in optimizing the design and manufacture of the subject aircraft propeller studied.

Structural Analysis of Cheju-style Plastic Greenhouse Model for Crop Growing Based on the Wind Load (풍하중을 고려한 제주형 작물재배용 비닐하우스모델의 구조해석)

  • 민창식;김용호;권기린
    • Journal of Bio-Environment Control
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    • v.7 no.3
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    • pp.181-190
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    • 1998
  • An elastic analysis under wind load was performed for the double layered plastic greenhouse model developed particularly for minimizing damages under typhoons at Cheju Citrus Research institute in Seagipo city. General EVA film was used for the inner covering and the developed special film which would break the wind pressure down was used for the outer covering. The wind tunnel test showed this special film reduced the wind speed up to 86 to 98% under well controlled situation. Based on the elastic analysis performed in the study, the behavior of the greenhouse was changed significantly due to the boundary conditions. Not like other researchers before we applied dead load of the concrete support to the ground pipe and fixed support boundary conditions at the 4 corner pipes. The analysis shows that the greenhouse was lifted and pulled the pipe out of the ground due to the sucking wind pressure. The behavior of the greenhouse was quite similar to that one real greenhouse failure. Therefore, not only we need to find the realistic boundary conditions for the supports, but also need to find how to rest the pipe supports on the ground without economic loss.

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체공형 부양선(Aerostat) 개념설계

  • Lee, Yung-Gyo;Kim, Dong-Min;Yeom, Chan-Hong
    • Aerospace Engineering and Technology
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    • v.4 no.1
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    • pp.31-38
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    • 2005
  • Conceptual design of an Aerostat was completed. Configuration was determined based on wind tunnel test results of aeostat hulls to have longitudinal static stability. Hull surface area and volume were obtained by using of Cubic spline method for given configuration and length. Final length of a hull was determined by iteration process. Cable tension and payload were estimated for conceptual design. A parametric study was performed for various weight and misson altitude. As results, a 30m class aerostat was designed and described.

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Evaluation of Yacht Sails Performance by CFD and Experiments (요트 세일의 성능에 관한 수치해석 및 실험)

  • Yoo Jae-Hoon;Ahn Hae-Seong
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.1
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    • pp.125-133
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    • 2006
  • It is important to understand flow characteristics and performances of sails for both sailors and designers who want to have efficient thrust of yacht In this Paper the viscous flows around sail-like rigid wings, which are similar to main and jib sails of a 30 feet sloop, are calculated using a CFD tool. Lift, drag and thrust forces are estimated for various conditions of gap distance between the two sails and the center of effort of the sail system is obtained. Wind tunnel experiments are also carried out to measure aerodynamic forces acting on the sails system and to validate the computation. It is found that the combination of two sails produces the lift force larger than the sum of that produced separately by each sail and the gap distance between the two sails is an important factor to determine total lift and thrust.