• Title/Summary/Keyword: 유동 운동학

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Development of an Unstructured 2-D Chimera Technique for Overlapped Bodies in Relative Motion (2차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체간의 상대운동 해석기법 개발)

  • An, Sang-Jun;Gwon, O-Jun;Jeong, Mun-Seung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.2
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    • pp.17-25
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    • 2006
  • In the present study, a 2-D chimera technique for overlapped bodies in relative motion is developed using unstructured triangular meshes. The solid boundary nodes located next to the intersecting point between bodies are merged to the intersecting point to assure accurate representation of the intersecting region. In order to assign proper value of flow variables at the nodes located out of the computational field, interpolation is conducted for non-active nodes. For validation, the motions of a NACA64A006 airfoil and a NACA0012 airfoil with a plane flap are computed and the results are compared with other simulations. The motion of a launching missile ejected from a NACA0012 airfoil is also simulated.

Experimental Study on the Characteristics of Turbulent Wall Pressure Fluctuation Over Compliant Coatings (유연재 코팅 평판의 난류 변동압력 특성에 관한 실험적 연구)

  • Park, Kyung-Hoon;Lee, Seung-Jae;Shin, Ku-Kyun
    • The Journal of the Acoustical Society of Korea
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    • v.26 no.6
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    • pp.293-300
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    • 2007
  • Turbulent boundary layer over an underwater vehicle is formed when it moves underwater and wall pressure fluctuation within the turbulent boundary layer generates flow-induced noise by exciting the elastic hull of the underwater vehicle. One of the methods to reduce this flow noise is to attach a compliant layer on the surface of the vehicle. In order to observe the possibility of noise reduction in the water when the compliant layer treatments are applied on the surface, three types of specimens those are a bare steel plate, a steel plate coated with neoprene and a steel plate with polyurethane coating material are tested at various flow speeds in a low noise cavitation tunnel. This paper presents the results of measurements and analysis of wall pressure fluctuations which is a main source of flow noise, within the turbulent boundary layer on three specimens. Its results could be shown that about 10dB reduction of wall fluctuation pressure at high frequencies was achieved due to the dissipation of turbulent energy by the compliant coating while it makes the turbulent boundary layer thicker and changes the behavior of turbulent flow in the layer.

A computational study on compressible flow of humid air around airfoil (익형 주위의 압축성 습공기 유동에 대한 수치 해석적 연구)

  • ;Zvi Rusak
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.4
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    • pp.1-7
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    • 2003
  • 습공기에 포함된 수증기가 상(Phase)변화를 일으킬 때 잠열이 발생하고 이 잠열은 익형 주위의 압축성 유동 상태량들을 변화시키므로, 이러한 열 증가가 유동에 끼치는 영향에 대하여 수치해석을 통하여 연구 수행하였다. 수치해석은 Rusak 과 Lee [1]가 최근에 연구 수행한 미교란 방법(small-disturbance approach)에 근거하여 이루어졌다. 고전적 핵 생성 모델과 작은 물방울 성장(droplet growth)모델을 이용한 이 방법에서는 비평형 균질 응축과정에서 일어나는 열 방출을 묘사한다. 응축에 의한 열전달, 압축성 유동의 운동에너지, 그리고 유동의 열적 상태량들 사이에서 일어나는 비선형 상호영향을 조사하고, 또한 주어진 문제를 지배가호 있는 상사 파라미터들을 제시하였다. 계산 결과들은 Euler 방정식을 사용하여 얻은 선행 수치계산들과 비교하여 잘 일치됨을 보였다. 상사법칙은 유동 동역학과 응축 상태량들이 상당히 비슷하게 거동하는 다양한 유동 형태들을 제안한다. 압축성 습공기 유동은 유체기계에 사용되는 익형들의 공력 성능을 증가시키는데 응용될 수 있다.

Numerical Analysis of the Vortex Shedding past a Square Cylinder with Moving Ground (지면 운동에 따른 정사각주 후류의 와류 유동장 수치 해석 Part I. 고정 지면과 이동 지면 비교)

  • Kim, Tae-Yoon;Lee, Bo-Sung;Lee, Dong-Ho;Kohama, Y.
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.6
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    • pp.1-7
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    • 2005
  • Incompressible Reynolds-averaged Navier-Stokes equations with $\varepsilon{-SST}$ turbulence model are adopted for the investigation of the flow fields between the square cylinder and the ground. When the grounds moves, the diminish of the shear layer intensity on the ground promotes the interaction between the lower and the upper separated shear layer of the cylinder. Hence vortex shedding occurs at the lower gap height than stationary ground. In the moving ground, the secondary shedding frequency disappears due to the absence of the separation bubble on the ground which exists in the stationary ground. In addition, the shedding frequency and aerodynamic coefficients in the moving ground become higher than those of the stationary ground.

A numerical simulation of flow around an impulsively translating two dimensional circular cylinder using the diffusion vortex method (순간적으로 병진운동하는 2차원 원형실린더 주위 유동장의 확산와류방법 연구)

  • Seo, Ho-Won
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.6
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    • pp.9-15
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    • 2004
  • In this study the development of the two dimensional flowfield around an impulsively translated circular cylinder is numerically simulated using the diffusion vortex method. A detailed streamline pattern of fore wake and main wake of Re=1200, 9500 flowfields are investigated. The results of streamline pattern, the size of main wake and the axial velocities along the rear symmetry axis of the circular cylinder show good agreement with the reported experimental results. The long term wake delvelopment for Re=1200 flowfield was calculated up to ${\tau}=50$. The vortex shedding frequency shows the similar value as that of reported.

Development of a 3-D Viscous Flow Solver Based on Unstructured Hybrid Meshes (비정렬 혼합 격자계 기반의 삼차원 점성 유동해석코드 개발)

  • Jung, Mun-Seung;Kwon, Oh-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.8
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    • pp.677-684
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    • 2007
  • In the Present Study, a 3-D viscous flow solver, based on unstructured hybrid meshses containing tetrahedra, prisms and pyramids, has been developed. A finite-volume discretization scheme is used for solving the compressible Navier-Stokes equations. A cell-vertex median dual volume is used for spatial discretization. The one-equation Spalart-Allmaras turbulence model has been adopted to evaluate the eddy viscosity. Validation were made by computing laminar and turbulent flows around a 3-D wing for steady flows and turbulent flows around an oscillating 3-D wing in harmonic motion for unsteady flows.

Chaos의 세계 I

  • 서용권
    • Journal of the KSME
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    • v.29 no.5
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    • pp.520-524
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    • 1989
  • chaos란 "질서 있는 무질서"를 의미한다. chaos의 큰 특징은 초기조건에의 민감성이다. 역으로 말 하면, 주어진 운동은 초기조건에 민감하므로 chaotic한 운동을 한다고 말할 수 있겠다. 제2장에서 는 유동문제의 대표격인 Lorenz chaos를 살펴보고, 3장에서는 동역학 문제인 Duffing-Holmes방 정식, 4장에서는 map의 대명사인 logistic map을, 5장에서는 기타 무수히 많은 분야 중 기계공 학에 가장 가까운 것들을 골라 연구된 내용을 소개하고 그 특징들을 살펴본다. 6장과 7장에서는 chaos의 정량화를 위한 Lyapunov지수와 fractal dimension의 개념과 그 계산 방법을 다룬다. 8 장에서는 현재까지도 그 의문이 풀리지 않은, chaos학문의 큰 관심사인, 난류의 시작문제를 취 급하고, 마지막으로 9장에서는 문제점, 과제 및 앞으로의 전망을 살펴보기로 한다. 살펴보기로 한다.

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The Study of The Comparison By the Displacement Term at Cylindercoordination Between The Junger and Feit's Cylinder Motion Equation and Newly produced Cylinder Motion Equation (Junger and Feit의 실린더운동방정식과 새로이 유도된 방정식에서 실린더좌표방향의 진폭항 비교 연구)

  • 조형국
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1997.06a
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    • pp.57-63
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    • 1997
  • 실린더 형태의 관은 산업체나 일반가정에서 자주 사용되어진다. 이러한 실린더 형태의 관들은 유체나 기체를 운반하는데 쓰이며, 운반과정에서 소음이 발생한다. 이러한 소음들의 해석은 우선실린더 방정식을유도하여야 한다. 음향학 분야에서 여러 가지 다른 형태의 실린더 운동 방정식이소개되었다. 예로써, Junger and Feit는 실린더의 벽이 매우 얇고 , 무한히 긴 실린더를 가정하에서 실린더운동방정식을 유동하였다. 본 논문에서는 참고문헌[5]에서 유도된 실린더운동방정식고 Junger and Feit 의 실린더운동방정식에서 실린더 좌표 방향으로 향하는 변위의 항을 비교하고, 임의의 실린더 크기를 가정하여 항의 차이를 그래프로 보였다.

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Development of an Unstructured Parallel Overset Mesh Technique for Unsteady Flow Simulations around bodies with Relative Motion (상대운동이 있는 물체주위의 비정상 유동해석을 위한 병렬화된 비정렬 중첩격자기법 개발)

  • Jung, Mun-Seung;Kwon, Oh-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.2
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    • pp.1-10
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    • 2005
  • An unstructured parallel overset mesh method has been developed for the simulation of unsteady flows around multiple bodies in relative motion. For this purpose, an efficient and robust search method is proposed for the unstructured grid system. A new data-structure is also proposed to handle the variable number of data on parallel sub-domain boundary. The interpolation boundary is defined for data communication between grid systems. An interpolation method to retain second-order spatial accuracy and to treat the points inside the neighboring solid bodies are also suggested. A single store separating from the Eglin/Pylon configuration is calculated and the result is compared with experimental data for validation. Simulation of unsteady flows around multiple bodies in relative motion is also performed.

Prediction of time-series underwater noise data using long short term memory model (Long short term memory 모델을 이용한 시계열 수중 소음 데이터 예측)

  • Hyesun Lee;Wooyoung Hong;Kookhyun Kim;Keunhwa Lee
    • The Journal of the Acoustical Society of Korea
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    • v.42 no.4
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    • pp.313-319
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    • 2023
  • In this paper, a time series machine learning model, Long Short Term Memory (LSTM), is applied into the bubble flow noise data and the underwater projectile launch noise data to predict missing values of time-series underwater noise data. The former is mixed with bubble noise, flow noise, and fluid-induced interaction noise measured in a pipe and can be classified into three types. The latter is the noise generated when an underwater projectile is ejected from a launch tube and has a characteristic of instantaenous noise. For such types of noise, a data-driven model can be more useful than an analytical model. We constructed an LSTM model with given data and evaluated the model's performance based on the number of hidden units, the number of input sequences, and the decimation factor of signal. It is shown that the optimal LSTM model works well for new data of the same type.