• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.821-832
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• 2011

Recently, the noise of vehicle is the one of the key factors for customers to purchase a vehicle and the most important part which is related to the noise is the exhaust system. Thus, car makers have their own ways to assess this exhaust noise not only to decrease the level of noise but to enhance the feeling of it. Typically, to do these things in the early stage of development, the tuning code of the exhaust system has to be made by CAE tool, which is very reliable but expensive, and the prototype parts of this code would be made for the validation test. Then this process can be iterated to meet the target of the performance. In this study, a new algorithm which adapts the '3 dimensional convective sound wave theory 'and 'Doppler effect' has been developed. With this new algorithm, a brand new system for the calculation of tail pipe noise has been developed and validated by acoustic wind tunnel test. As a result of this study, various comparisons and have been carried out, for example, the comparison with other CAE tool has been performed for the validity and the improvement of the new calculation code could be achieved.

• 한국항공우주학회지
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• 제46권5호
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• pp.376-384
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• 2018

본 연구에서는 투과면을 이용하는 음향상사법으로 제자리 비행하는 UH-1H 로터 블레이드 주위의 원방 소음을 예측하였다. 두께 소음과 하중 소음, 그리고 충격파 및 끝단 후류 등에 의해 발생하는 유동 소음을 예측하기 위해 블레이드 표면을 포함하는 투과면을 구성하였다. 3차원 압축성 Euler 방정식 및 Navier-Stokes 방정식을 적용하여 공력 해석을 수행하고 비교하였다. 투과면의 위치에 따라 High Speed Impulsive 소음을 예측 및 검증하였다. 블레이드 끝단에서 발생하는 충격파에 의한 소음원이 지배적인 요소임을 확인하였으며, 충격파를 온전히 포함하도록 투과면을 구성하는 것이 중요함을 보였다.

• 한국철도학회논문집
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• 제17권4호
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• pp.233-244
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• 2014

이 연구에서는 자기부상열차-가이드웨이 상호작용 해석기법을 현장에서 계측된 자료를 활용하여 검증한다. 자기부상열차의 차체와 대차는 병진운동과 회전운동을 하는 강체 질량으로 모사한다. 대차의 부상전자석에서 발생하는 부상력은 능동 제어 알고리즘에 의해 제어된다. 가이드웨이는 Euler-Bernoulli beam을 사용하여 수치 모형을 구성한다. 대차의 회전 운동으로 인한 부상공극의 변화와 가이드웨이에 작용하는 위치의 변화를 엄밀히 고려하여 자기부상열차-가이드웨이 상호작용계의 동적거동 해석을 수행한다. 인천공항 자기부상철도 노선에서 계측된 실측 자료를 이용하여 해석기법을 검증한다. 해석 결과와 현장 계측 결과의 비교를 통해 해석 기법의 정확성을 검증하고, 대상 구조물이 설계 기준을 만족하도록 안전하게 설계되고 시공되었음을 확인한다.

• Water Engineering Research
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• 제3권2호
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• pp.75-84
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• 2002

An Euler-Lagrange two-phase flow model is presented fur simulation sheet-flow transport under wave and current. The flow is computed by solving the Reynolds Averaged Navier-Stokes equation in conjunction with the k-$\varepsilon$ turbulence model for turbulence closure. The sediment transport is introduced as a motion of granular media under the action of unsteady flow from the Lagragian point of view. In other word, motion of every single particle is numerically traced with Movable Bed Simulator (MBS) code based on the Distinct Element Method (DEM), in which the frequent interparticle collision of the moving particles during the sheet-flow transport is sophisticatedly taken into account. The particle diameter effect on time-dependent developing process of sheet-flow transport is investigated, by using three different diameter sizes of sediment. The influence of an imposed current on oscillatory sheet-flow transport is also investigated. It is concluded that the sediment transport rate increases due to the relaxation process related to the time-lag between flow velocity and sediment motion.

• 한국전산유체공학회지
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• 제20권2호
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• pp.103-108
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• 2015

Fluid-body interaction analysis of floating body with six degree-of-freedom motion is presented. In this study, three-dimensional incompressible Navier-Stokes equations are employed as a governing equation. The numerical method is based on a finite-volume approach on a cartesian grid together with a fractional-step method. To represent the body motion, the immersed boundary method for direct forcing is employed. In order to simulate the coupled six degree-of-freedom motion, Euler's equations based on rigid body dynamics are utilized. To represent the complex body shape, level-set based algorithm is utilized. In order to describe the free surface motion, the volume of fluid method utilizing the tangent of hyperbola for interface capturing scheme is employed. This study showed three different continuums(air, water and body) are simultaneously simulated by newly developed code. To demonstrate the applicability of the current approach, two different problems(dam-breaking with stationary obstacle and water entry) are simulated and all results are validated.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.588-594
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• 2001

본 연구를 통해 초음속 전투기 날개의 공력-구조를 동시에 고려한 다학제간 설계를 수행하였다. 공력해석을 위해 사용된 3 차원 Euler Code는 수렴 속도를 개선하기 위해 Multigrid를 적용하였으며, 3차의 transfinite interpolation을 사용하여 O-H type의 공력해석 격자계를 생성하였다. 구조 분야는 절점당 54개의 자유도를 가지는 9 절점 쉘 혼합 유한요소(9-node shell mixed finite element)를 사용하여 해석을 수행하였다. 설계변수는 공력쪽으로 날개의 평면형상에 관련된 변수 3개, 구조쪽은 날개 윗면과 아래면의 표피두께에 관련된 4개의 설계변수 사용하였으며, D-optimality 조건을 만족시키는 실험점들에 대해 공력해석과 구조해석이 연동된 정적 공탄성 해석을 수행한 후, 반응면 기법을 이용하여 목적함수와 제약조건에 대한 반응면을 구성하였다. 단일점 설계를 수행한 후 이를 바탕으로 3개의 설계점을 동시에 고려한 다점 설계를 수행하였으며, 공력만을 고려한 설계 결과와 공력-구조를 동시에 고려한 다학제간 설계결과의 비교를 통해 다학제간 설계의 타당성과 우수성을 입증하였다.

• 대한기계학회논문집B
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• 제22권6호
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• pp.757-770
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• 1998

A Navier-Stokes code with a low Reynolds number k-.epsilon. turbulence model was tested to investigate its predictability for the unsteady transitional boundary layer flow due to rotor-stator interaction. A preliminary calculation with three different numbers of time steps 300, 600, and 1000 for a rotor wake passing period was carried out to see the effects of time steps on the unsteady flow and pressure fields due to rotor-stator interaction. Numerical solutions showed that unsteady pressure was much more sensitive to the number of time steps and over 600 time steps should be used to get a numerical solution independent of the number of time steps for a rotor wake passing period. The original low Reynolds number k-.epsilon. turbulence model showed very poor prediction of the unsteady transitional boundary layer flow due to rotor-stator interaction. This was due to the excessive production of turbulent kinetic energy near the leading edge. A modification suggested by Launder was incorporated and the modified model captured well the wake induced transitional strip. Present solutions also showed improved prediction over previous Euler/boundary layer solution in terms of the onset of unsteady transition and its extent.

• 대한기계학회논문집B
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• 제22권6호
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• pp.771-787
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• 1998

A Navier-Stokes code with a modified low Reynolds number k-.epsilon. turbulence model was used to study the unsteady transitional boundary layer flow due to rotor-stator interaction. The modification, proposed by Launder, to improve prediction of stagnation flows was incorporated to the low Reynolds number k-.epsilon. turbulence model by Fan-Lakshminarayana-Barnett. Numerical solution is shown to capture well the calmed laminar flow as well as the wake induced transitional strip due to rotor-stator interaction and shows improvement, in terms of onset of transition and its length, over previous Euler/boundary layer solution. The turbulent kinetic energy shows local maximum along the upstream rotor wake in the wake induced transitional strip and this characteristics is observed untill the end of transition. The wake induced strip also shown apparent even in the laminar sublayer as the upstream rotor wake penetrates inside the boundary layer.

• 한국인터넷방송통신학회논문지
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• 제12권6호
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• pp.141-146
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• 2012

본 논문에서는 영상 기반 자동 착륙 시스템 개발과 이 시스템을 사용하는 멀티로터 플랫폼 개발에 대해서 소개 한다. 멀티로터 플랫폼은 뉴턴 오일러 개념을 근간으로 하는 강체 운동 모델링을 하였고, LQR 제어 기법을 통한 제어기 튜닝 및 시뮬레이션을 하였다. 영상기반 자동 착륙 시스템은 멀터로터 시스템에 탑재된 단일 카메라를 사용하여 추가적인 임무장비 없이 증강 현실 알고리즘을 사용하여 마커를 탐지하고 정밀한 착륙을 유도하도록 GCS와 연동 코드를 구현 하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제26권5호
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• pp.596-606
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• 2002

The three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, PAM-FLOW based on FEM method has been applied to analyze the flow field around the high speed train which is entering into a channel. From the present study, the pressure and flow transients were calculated and analyzed. The generation of compression wave was observed ahead of train and the high pressure in the gap between the train and the tunnel was also found due to the blockage effects. It was found that abrupt fluctuation in pressure exists in the region from train nose to shoulder of train corresponding to 10％ of total length of train during tunnel entry. Computed time history of aerodynamic forces of train during tunnel entry show that drag coefficient rapidly rises and saturates at about non-dimensional time 0.31. The total increase of drag coefficient before and after tunnel entry is about 1.1%. Transient profile of lift force shows similar pattern to drag coefficient except abrupt drop after saturation and lift force in the tunnel increases 0.08% more than that before tunnel entry.