• 한국수자원학회논문집
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• 제30권6호
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• pp.761-768
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• 1997

열발전소에서 비상 가동중단으로 냉각수 배수계통에 발생하는 비압축성 부정류를 해석하는 수치모형이 개발되었다. 개발된 수치모형은 냉각수 기계내부계통, 폐정, 공기실, 관로, 맨홀, 개수로 및 바다 등에 의한 복잡한 흐름에 대해 전체적인 부정류거동을 동시에 해석할 수 있는 기능을 가진다. 수치해법으로는 leap-forg 유한차분법을 적용하였으며, 간단한 경우에 대한 모형의 검증과 함께, 종래 배수암거 하류단에 적용되덕 고정수위경계조건에 대한 검토가 이루어졌다.

• 한국해양공학회지
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• 제25권4호
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• pp.36-41
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• 2011

In the present paper, a direct forcing/fictitious domain (DF/FD) level set method is proposed to simulate the FSI (fluid-solid interaction) in two-phase flow. The main idea is to combine the direct-forcing/fictitious domain (DF/FD) method with the level set method in the Cartesian coordinates. The DF/FD method is a non-Lagrange-multiplier version of a distributed Lagrange multiplier/fictitious domain (DLM/FD) method. This method does not sacrifice the accuracy and robustness by employing a discrete ${\delta}$ (Dirac delta) function to transfer quantities between the Eulerian nodes and Lagrangian points explicitly as the immersed boundary method. The advantages of this approach are the simple concept, easy implementation, and utilization of the original governing equation without modification. Simulations of various water-entry problems have been conducted to validate the capability and accuracy of the present method in solving the FSI in two-phase flow. Consequently, the present results are found to be in good agreement with those of previous studies.

• 한국전산유체공학회지
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• 제11권2호
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• pp.8-18
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• 2006

A CFD benchmark calculation for a steam blowdown test was performed for 30 seconds to develop the methodology of numerical analysis for the thermal mixing between steam and subcooled water. In the CFD analysis, the grid model simulating the sparger and the IRWST pool were developed by the axisymmetric condition and then the steam condensation phenomena by a direct contact was modelled by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, a turbulent flow, and a buoyancy flow. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small temperature difference was locally found at some locations. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distribution and a proper numerical method are adopted.

• 한국주조공학회지
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• 제31권3호
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• pp.124-129
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• 2011

We applied two numerical schemes to improve accuracy of the solution in the flow simulation of molten metal. One method is Piecewise Linear Interface Calculation (PLIC) method and the other is Donor-Acceptor (D-A) method. In the present work, we have tested simple problems to verify the module of the interface reconstruction algorithms. After validations, accuracy and efficiency of these two methods have compared by simulating various real products. On the numerical simulation of free surface flow, it is possible for PLIC method to track very accurately the interface between phases. PLIC method, however, has the weak point where a lot of computational time hangs, though it shows the more accurate interface reconstruction. Donor-Acceptor method has enough effectiveness in the macro observation of mold filling sequence though it shows the inferior accuracy.

• Ocean Systems Engineering
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• 제1권1호
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• pp.31-57
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• 2011

Impact pressure due to sloshing is of great concern for the ship owners, designers and builders of the LNG carriers regarding the safety of LNG containment system and hull structure. Sloshing of LNG in partially filled tank has been an active area of research with numerous experimental and numerical investigations over the past decade. In order to accurately predict the sloshing impact load, a new numerical method was developed for accurate resolution of violent sloshing flow inside a three-dimensional LNG tank including wave breaking, jet formation, gas entrapping and liquid-gas interaction. The sloshing flow inside a membrane-type LNG tank is simulated numerically using the Finite-Analytic Navier-Stokes (FANS) method. The governing equations for two-phase air and water flows are formulated in curvilinear coordinate system and discretized using the finite-analytic method on a non-staggered grid. Simulations were performed for LNG tank in transverse and longitudinal motions including horizontal, vertical, and rotational motions. The predicted impact pressures were compared with the corresponding experimental data. The validation results clearly illustrate the capability of the present two-phase FANS method for accurate prediction of impact pressure in sloshing LNG tank including violent free surface motion, three-dimensional instability and air trapping effects.

• 반도체디스플레이기술학회지
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• 제5권3호
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• pp.29-32
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• 2006

Because of new requirements related to the employment of SMT(Surface Mounting Technology) manufacturing and the diversity of components on high density PCB(Printed Circuit Boards), Thermal control of the reflow process is required in order to achieve acceptable yields and reliability of SMT assemblies. Accurate control of the temperature distribution during the reflow process is one of the major requirements, especially in lead-free assembly. This study has been performed for reflow process using the commercial CFD(Computational Fluid Dynamics) tool for predicting flow and temperature distributions. Porous plate was installed to prevent leakage flow which was one of the major problem of temperature uniformity in the reflow process. There is a separation region where the flow is turned. Outside wall made of porous plate is to prevent and minimize separation region for acquiring uniform temperature during operation. This paper provided design concept from CFD results of the steady state temperature distribution and flow field inside a reflow oven.

• 대한기계학회논문집
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• 제13권3호
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• pp.337-344
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• 1989

본 연구에서는 플래쉬(flash)를 가진 축대칭 리브-웨브형(rib-web type) 제품의 형단조가공을 해석하기 위한 UBET 프로그램을 개발하고 변형중의 경계 조건처리를 다르게 한 세 가지 유동모델에 대하여 소재의 유동상태와 단조하중을 계산하여 효과적인 유동모델을 제시하였다. 또한 체적은 같으나 반지름과 높이의 비가 다른 몇 가지 초기소재 형상에 대하여 변형에 따른 소재의 다이충만도 및 하중을 비교하여 적절한 초기소재의 형상을 찾고자 하였다. 본 연구에서 제시한 유동모델의 효율성을 검증하기 위하여 플라스씬(plasticine) 소재를 사용한 실험과 그 결과를 비교, 분석하였다.

• 한국가시화정보학회지
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• 제19권3호
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• pp.106-114
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• 2021

In the present study, we investigate the flow characteristics of a paraglider canopy with leading-edge tubercles by performing force measurement and surface flow visualizations. The experiment is conducted at Re = 3.3×10⁵ in a wind tunnel, where Re is the Reynolds number based on the mean chord length and the free-stream velocity. The canopy model with leading-edge tubercles has flow characteristics of a two-step stall, showing an earlier onset of the first stall than the canopy model without leading-edge tubercles. However, the main stall angle of the tubercled model is much larger than that of the canopy model without tubercles, resulting in a higher aerodynamic performance at high angles of attack. The delay in the main stall is ascribed to the suppression of separation bubble collapse around the wingtip at high angles of attack.

• Journal of Microbiology and Biotechnology
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• 제29권5호
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• pp.749-757
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• 2019

Nitrilase is a valuable hydrolase that catalyzes nitriles into carboxylic acid and ammonia. Its applications, however, are severely restricted by the harsh conditions of industrial reaction processes. To solve this problem, a nitrilase from Acidovorax facilis 72W was inserted into an Escherichia coli-Bacillus subtilis shuttle vector for spore surface display. Western blot, enzyme activity measurements and flow cytometric analysis results all indicated a successful spore surface display of the CotB-nit fusion protein. In addition, the optimal catalytic pH value and temperature of the displayed nitrilase were determined to be 7.0 and $50^{\circ}C$, respectively. Moreover, results of reusability tests revealed that 64% of the initial activity of the displayed nitrilase was still retained at the $10^{th}$ cycle. Furthermore, hydrolysis efficiency of upscale production of cyanocarboxylic acid was significantly higher in the displayed nitrilase-treated group than in the free group expressed by E. coli (pET-28a-nit). Generally, the display of A. facilis 72W nitrilase on the spore surface of Bacillus subtilis may be a useful method for immobilization of enzyme and consequent biocatalytic stabilization.

• 한국수자원학회논문집
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• 제56권spc1호
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• pp.1037-1048
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• 2023

하천에 설치된 댐, 보 등과 같은 횡단구조물은 수생태계에 영향을 미치며 종적 연결성을 단절하기 때문에 어류의 이동을 확보하기 위하여 어도가 설치된다. 그러나 어도 내부의 흐름 특성 및 어종에 따라 어류의 통과효율의 차이가 발생한다. 본 연구에서는 3차원 RANS 모형과 자유수면 해석을 위한 VOF (volume of fluid)기법을 적용한 수치모형을 활용하여 계단식 어도에서 발생하는 난류흐름을 수치모의 하였다. 계단식 어도의 pool의 길이 변화 및 상류 수위 변동을 고려하였으며 이들의 변화에 따라 평균유속 및 난류운동에너지 분포를 분석하였다. 표면류 및 잠입류 특성을 잘 재현하였으며 pool의 길이가 증가하면서 표면류에서 잠입류로 변화하였고 상류 수위가 증가함에 따라 표면류 특성이 명확하게 나타났다. 어도 내 어류의 이동과 관련된 수리학적 인자는 유속 및 난류운동에너지 등이 있으며 이를 바탕으로 어류의 소상 가능성을 검토하였다.