• KIEAE Journal
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• 제17권1호
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• pp.69-75
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• 2017

Purpose: Heat transfer analysis of recently developed 'slim type double-skin system window' were presented. This window system is designed for curtain wall type façade that main energy loss factor of recent elegant buildings. And the double skin system is the dual window system integrated with inner shading component, enclosed gap space made by two windows when both windows were closed and shading component effectively reflect and terminate solar radiation from outdoor. Usually double-skin system requires much more space than normal window systems but this development has limited by 270mm, facilitated for curtain wall façade buildings. In this study, we estimated thermophysical phenomena of our double-skin curtain wall system window with solar load conditions at the summer season. Method: A fully 3-Dimentional analysis adopted for flow and convective and radiative heat transfer. The commercial CFD package were used to model the surface to surface radiation for opaque solid region of windows' frame, transparent glass, fluid region at inside of double-skin and indoor/outdoor environments. Result: Steep angle of solar incident occur at solar summer conditions. And this steep solar ray cause direct heat absorption from outside of frame surface rather than transmitted through the glass. Moreover, reflection effect of shading unit inside at the double-skin window system was nearly disappeared because of solar incident angle. With this circumstances, double-skin window system effectively cuts the heat transfer from outdoor to indoor due to separation of air space between outdoor and indoor with inner space of double-skin window system.

• 공업화학
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• 제34권3호
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• pp.307-312
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• 2023

본 연구는 수소 경제 사회의 안전 확보를 위해 수소 연료전지 후단 배출된 미반응 수소를 안정적으로 산화하는 방안에 대해 논의하였다. 안전 시스템은 미반응 수소를 에너지원 없이 제거할 수 있는 상온 산화촉매를 충진하였으며, 이때 반응으로 배출되는 산화열은 안정적으로 회수할 수 있는 열 회수 장치를 연계하고자 하였다. 그 결과, 수소 산화 시스템의 충진 조건에 따라 시스템 내 압력 및 유체 흐름이 변화함을 CFD 분석을 통해 확인하였다. 또한 배가스 온도, 열 회수기 내 유량 및 압력조건을 최적화하여 300 ℃ 이상의 배가스 산화 열원을 40 ℃ 이상의 온수를 확보하는 방식으로 폐열을 회수할 수 있음을 확인하였다. 본 연구를 통해 수소 연료전지와 같은 중·소규모 사업장에 적용된 수소 활용 공정을 실증 규모로 평가하여 안전 시스템으로의 가능성을 확인하였다. 추후 실증화 연구를 통해 예측하지 못한 수소 안전사고에 대해 대응할 수 있는 안전 가이드로 활용될 수 있다고 판단된다.

• 인터넷정보학회논문지
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• 제17권6호
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• pp.71-79
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• 2016

컴퓨터 성능이 발전하면서 물리, 화학, 재료과학, 생명과학 등에 이용하는 계산과학(Computational Science)이 주목을 받고 있다. 국내에서는 이러한 계산과학 문제를 해결하기 위해 학생 및 연구자들이 EDISON 플랫폼을 이용하고 있다. EDISON 플랫폼은 5개 분야(전산열유체, 나노물리, 계산화학, 구조동역학, 전산설계)문제 해결 환경을 위한 교육-연구용 웹 포털을 제공하는 서비스이다. 시스템의 규모 및 사용자층이 늘어남에 따라, 서비스 제공뿐만 아니라 실제 운영되는 시스템의 데이터 관리 체계를 효율적으로 운용할 필요성이 대두되고 있다. 본 논문에서는 기존 EDISON 플랫폼과 웹 포털 간의 데이터 동기화 문제를 해결하였고, EDISON 웹 포털이 통합됨에 따라, 사용자의 데이터 및 파일을 통합 관리하기 위해서 EDISON 플랫폼의 파일관리 서비스를 구현하여 파일관리 효율성을 향상 시켰다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.671-679
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• 2008

The effect of Pre-cooled Turbojet Engine installation and nozzle exhaust jet on Hypersonic Turbojet EXperimental aircraft(HYTEX aircraft) were investigated by three-dimensional numerical analyses to obtain aerodynamic characteristics of the aircraft during its in-flight condition. First, simulations of wind tunnel experiment using small scale model of the aircraft with and without the rectangular duct reproducing engine was performed at M=5.1 condition in order to validate the calculation code. Here, good agreements with experimental data were obtained regarding centerline wall pressures on the aircraft and aerodynamic coefficients of forces and moments acting on the aircraft. Next, full scale integrated analysis of the aircraft and the engine were conducted for flight Mach numbers of M=5.0, 4.0, 3.5, 3.0, and 2.0. Increasing the angle of attack $\alpha$ of the aircraft in M=5.0 flight increased the mass flow rate of the air captured at the intake due to pre-compression effect of the nose shockwave, also increasing the thrust obtained at the engine plug nozzle. Sufficient thrust for acceleration were obtained at $\alpha=3$ and 5 degrees. Increase of flight Mach number at $\alpha=0$ degrees resulted in decrease of mass flow rate captured at the engine intake, and thus decrease in thrust at the nozzle. The thrust was sufficient for acceleration at M=3.5 and lower cases. Lift force on the aircraft was increased by the integration of engine on the aircraft for all varying angles of attack or flight Mach numbers. However, the slope of lift increase when increasing flight Mach number showed decrease as flight Mach number reach to M=5.0, due to the separation shockwave at the upper surface of the aircraft. Pitch moment of the aircraft was not affected by the installation of the engines for all angles of attack at M=5.0 condition. In low Mach number cases at $\alpha=0$ degrees, installation of the engines increased the pitch moment compared to no engine configuration. Installation of the engines increased the frictional drag on the aircraft, and its percentage to the total drag ranged between 30-50% for varying angle of attack in M=5.0 flight.

• 한국전산유체공학회지
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• 제20권2호
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• pp.23-36
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• 2015

The $2^{nd}$ generation ice accretion analysis program has been developed and validated for various icing conditions. The essential feature of the $2^{nd}$ generation code lies in its capability of handling general 3-D geometry and improved accuracy. The entire velocity fields are obtained based on Navier-Stokes equations in order to take the massively separated flow field into account. Unlike $1^{st}$ generation code, the droplet trajectories are calculated using Eulerian approach, which is adopted to yield appropriate collection efficiency even in the shadow region. For improved thermodynamic analysis on the surfaces, water film model and modified Messinger model are newly included in the present analysis. The ice shape for a given time step is obtained by considering the exact amount of ice accreted on the surface. Each module of the icing analysis code has been seamlessly integrated on the OpenFOAM platform. The developed code was validated against available experimental data for 2D airfoils and 3D DLR-F4. Due to the lack of experimental data, the computed results of DLR-F4 were compared with those obtained from FENSAP-ICE, which is state-of-the-art 3D icing analysis code. It was clearly shown that the present code produces comparable results to those of FENSAP-ICE, in terms of prediction accuracy and the capability of handling general 3-D geometries.

• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.105-112
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• 2013

The application of contra-rotating rotors for higher specific speed pump has been proposed in our studies, which is in principle effective for reducing the rotational speed and/or the pump size under the same specification of conventional axial flow pump. In the previous experiments of our prototype, the cavitation inception at the tip region of the rear rotor rather than that of the front rotor and the strong potential interaction from the suction surface of the rear rotor blade to the pressure surface of the front one were observed, indicating the possibility to further improve the pump performance by optimizing rotational speed combination between the two rotors. The present research aims at the design of rear rotor with lower rotational speed. Considering the fact that the incoming flow velocity defects at the tip region of the rear rotor, an integrated inflow model of 'forced vortex' and 'free vortex' is employed. The variation of maximum camber location from hub to tip as well as other related considerations are also taken into account for further performance improvement. The ideas cited above are separately or comprehensively applied in the design of three types of rear rotor, which are subsequently simulated in ANSYS CFX to evaluate the related pump performance and therefore the whole low speed design idea. Finally, the experimental validation is carried out on one type to offer further proofs for the availability of the whole design method.

• Wind and Structures
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• 제23권4호
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• pp.313-350
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• 2016

Taipei 101 Tower, which has 101 stories with height of 508 m, is located in Taipei where typhoons and earthquakes commonly occur. It is currently the second tallest building in the world. Therefore, the dynamic performance of the super-tall building under strong wind actions requires particular attentions. In this study, Large Eddy Simulation (LES) integrated with a new inflow turbulence generator and a new sub-grid scale (SGS) model was conducted to simulate the wind loads on the super-tall building. Three-dimensional finite element model of Taipei 101 Tower was established and used to evaluate the wind-induced responses of the high-rise structure based on the simulated wind forces. The numerical results were found to be consistent with those measured from a vibration monitoring system installed in the building. Furthermore, the equivalent static wind loads on the building, which were computed by the time-domain and frequency-domain analysis, respectively, were in satisfactory agreement with available wind tunnel testing results. It has been demonstrated through the validation studies that the numerical framework presented in this paper, including the recommended SGS model, the inflow turbulence generation technique and associated numerical treatments, is a useful tool for evaluation of the wind loads and wind-induced responses of tall buildings.

• 대한기계학회논문집A
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• 제29권10호
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• pp.1289-1297
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• 2005

The flow in a microchannel is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved. In this regard, we developed a novel chaotic micromixer, named Serpentine Laminating Micromixer (SLM) in the present study, Part 1. In the SLM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms: splitting/recombination and chaotic advection. The splitting and recombination (in other term, lamination) mechanism is obtained by the successive arrangement of 'F'-shape mixing units in two layers. The chaotic advection is induced by the overall three-dimensional serpentine path of the microchannel. Chaotic mixing performance of the SLM was fully characterized numerically. To compare the mixing performance, a T-type micromixer which has the same width, height and length of the SLM was also designed. The three-dimensional numerical mixing simulations show the superiority of the SLM over the T-type micromixer. From the cross-sectional simulation results of mixing patterns, the chaotic advection effect from the serpentine channel path design acts favorably to realize the ideal lamination of fluid flow as Re increases. Chaotic mixing mechanism, proposed in this study, could be easily integrated in Micro-Total-Analysis-System, Lab-on-a-Chip and so on.

• 플랜트 저널
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• 제12권3호
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• pp.24-31
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• 2016

풍진동(Wind-induced vibration)은 바람에 의해 구조물에 진동이 발생하는 현상으로써 세장비가 큰 열기기 Stack 설계시 고려해야 할 중요한 사항이다. 따라서, 국제 규격에는 풍진동에 대한 설계 인자와 각 범위에 대해 필요한 고려 사항을 정의하고 있다. 규격에 의한 설계 검증은 몇몇 인자를 이용하여 간단하게 확인이 가능하다는 장점이 있는 반면, 실제 풍진동에 의한 영향을 정량적으로 평가하지 않기 때문에 실제 필요한 것보다 과도한 설계를 요구할 수 있다는 단점이 있다. 또한 여러 제약조건으로 Code 상의 요구조건을 만족하지 못하는 경우 실제 시스템의 거동을 예측할 수 없다는 단점이 있다. 이러한 점을 보완하기 위해 CFD 와 FEM 등의 수치적 해석 방법을 통해 풍진동이 실제 Stack에 미치는 영향을 해석하여 설계 적정성을 검증하여 Code 상의 요구 조건과 비교하였다.

• Steel and Composite Structures
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• 제10권2호
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• pp.129-149
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• 2010

The objective of this study is to formulate a general 3D material-structural analysis framework for the thermomechanical behavior of steel-concrete structures in a fire environment. The proposed analysis framework consists of three sequential modeling parts: fire dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of the structure. The first modeling part consists of applying the NIST (National Institute of Standards and Technology) Fire Dynamics Simulator (FDS) where coupled CFD (Computational Fluid Dynamics) with thermodynamics are combined to realistically model the fire progression within the steel-concrete structure. The goal is to generate the spatial-temporal (ST) solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST solutions are generated in a discrete form. Continuous FDS-ST approximations are then developed to represent the temperature or heat-flux at any given time or point within the structure. An extensive numerical study is carried out to examine the best ST approximation functions that strike a balance between accuracy and simplicity. The second modeling part consists of a finite-element (FE) transient heat analysis of the structure using the continuous FDS-ST surface variables as prescribed thermal boundary conditions. The third modeling part is a thermomechanical FE structural analysis using both nonlinear material and geometry. The temperature history from the second modeling part is used at all nodal points. The ABAQUS (2003) FE code is used with external user subroutines for the second and third simulation parts in order to describe the specific heat temperature nonlinear dependency that drastically affects the transient thermal solution especially for concrete materials. User subroutines are also developed to apply the continuous FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The proposed modeling framework is applied to predict the temperature and deflection of the well-documented third Cardington fire test.