• 대한기계학회논문집B
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• 제20권11호
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• pp.3607-3619
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• 1996

Experimental and numerical studies for three-dimensional pulsatile flows are conducted to investigate the flow characteristics in the bifurcated tubes. Velocity measurements in experimental study were made by both Pulsed Doppler Ultrasound(PDU) machine and Laser Doppler Anemometer(LDA) system. Glycerin is used for experimental study. Experimental results are used to verify the results of the numerical simulation. Flow characteristics of Newtonian fluid and blood in the bifurcated tubes under the steady and pulsatlie flows are numerically investigated. Finite volume method is employed for three-dimensional numerical simulations. Blood is considered as a non-Newtonian fluid and the constitutive equation of blood is used for the numerical analysis. Numerical analyses are focused on the flow patterns for various branch angles ranging from 30.deg. to 90.deg. and diameter ratios such as 1.0, 0.8, and 0.6. Pulsatile flow characteristics of blood are compared with those of Newtonian fluid. Parameter effects on axial velocity, pressure and wall shear stress distribution along the bifurcated tubes are discussed in terms of the branch angle, diameter ratio, and Reynolds number.

• 한국기계가공학회지
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• 제11권6호
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• pp.28-35
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• 2012

This study is on SCR reactor, NOx reduction system in Marine that has been an issue nowadays. Especially design data was obtained by numerical on flow uniformity that is one of the design factor in SCR reactor. Also pressure drop on catalyst size inserted into SCR reactor was compared by experiment and numerical analysis. S/W, numerical analysis used for this study was confirmed that the result of numerical analysis used STAR-CCM+, common use CFD code, pressure drop on catalyst is not big different from the result of numerical analysis. In addition, degree of uniformity of liquid on SCR reactor was over 0.9. Whereas it was assured that degree of uniformity of liquid was changed depends on the shape of pipe at the entrance of SCR.

• 한국도로학회논문집
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• 제18권1호
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• pp.73-83
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• 2016

PURPOSES : The purpose of this study is to develop a method for improving the accuracy of analysis results obtained from a two-dimensional (2-D) numerical analysis model of continuously reinforced concrete pavement (CRCP). METHODS : The analysis results from the 2-D numerical model of CRCP are compared with those from more rigorous three-dimensional (3-D) models of CRCP, and the relationships between the results are recognized. In addition, the numerical analysis results are compared with the results obtained from field experiments. By performing these comparisons, the calibration factors used for the 2-D CRCP model are determined. RESULTS : The results from the comparisons between 2-D and 3-D CRCP analyses show that with the 2-D CRCP model, concrete stresses can be overestimated significantly, and crack widths can either be underestimated or overestimated by a slight margin depending on the assumption of plane stress or plane strain. The behaviors of crack width in field measurements are comparable to those obtained from the numerical model of CRCP. CONCLUSIONS : The accuracy of analysis results from the 2-D CRCP model can be improved significantly by applying calibration factors obtained from comparisons with 3-D analyses and field experiments.

• 한국지구과학회지
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• 제30권4호
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• pp.464-477
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• 2009

호수에 의한 국지 순환의 영향을 조사하기 위하여 대청호수 주변에 대하여 수치 실험을 수행하고 국지 순환의 형태를 연구하였다. WRF 모델로부터 예보된 지상 기온은 관측보다 작으며, 풍속은 모델에서 관측보다 강하게 모의됨을 보였다. 호수 주변의 국지 순환은 호수와 주변 지면과의 열적 차이에 의해 발생하는 호수풍이 특징적이었다. 대청호수에서는 호수풍이 09 LST에 발생하며, 15 LST에 최대를 보이고 18 LST에 소멸하였다. 수치 모의된 연직 순환의 높이는 1,200m를 나타냈다. 비습의 분포는 낮 시간동안 호수풍 순환에 의해 호수위의 습윤한 공기의 내륙 이동으로 주위 지면에서 증가함을 보였다. 호수를 제거한 민감도 실험에서 호수가 존재할 때 주위 지면 온도가 감소함을 보였다. 호수 지표이용도를 초원으로 변경하였을 때 호수 주변의 기상관측소에서 풍속은 증가하였다. 수치실험은 호수로부터 발생된 호수풍 순환이 주위 대기경계층 기상에 영향을 주고 있음을 지시한다.

• 대한토목학회논문집
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• 제33권5호
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• pp.1777-1783
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• 2013

유량측정방법 중에서 파샬플륨을 이용하는 방법은 유속이 매우 느리거나 토사유입이 많은 지점에서 상대적으로 유리하다. 국제표준화기구(ISO : International Organization for Standardization)에 파샬플륨의 규모별 규격화된 경험식이 제시되어 있지만, 규격을 따르지 않는 파샬플륨에 대한 수리실험이나 수치모의를 통한 연구는 다소 부족한 실정이다. 따라서 본 연구에서는 ISO 규격 파샬플륨에 대하여 경험식과 수치모의를 비교하여 파샬플륨에 대한 수치모의의 적정성을 검토하였고 현장 여건 등의 이유로 ISO 규격을 따르지 않는 파샬플륨은 유량산정공식을 얻기 위해서 수리실험을 수행해야만 했다. 이러한 임의형상의 파샬플륨에 대하여 동일 조건의 수리실험 및 수치모의 결과를 비교 검토하였다. 그 결과 수치모의가 파샬플륨의 수심과 유량을 적절하게 모의하고 있음을 확인하였다. 이 결과를 이용하여 임의형상에 대한 무차원 유량산정공식을 도출하였으며, 식을 통해 산정된 값과 실험값을 비교하였다. 그 결과 오차는 최대 2.3%로 나타났다. 파샬플륨의 규모결정시 실제 지형과 유입부 형상 등을 고려한 수치모의를 수행한다면 수치모의에 기초한 유량산정공식을 쉽게 도출 할 수 있을 것이다. 또한, 복잡한 수행과정으로 인해 오차가 발생하기 쉬운 수리모형실험을 경제적으로 보완할 수 있을 것으로 판단된다.

• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.363-371
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• 2011

In this paper, a three-dimensional hydrogen desorption model is developed to precisely study the hydrogen desorption kinetics and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The metal hydride hydrogen desorption model, i.e. governed by the conservation of mass, momentum, and thermal energy is first experimentally validated against the temperature evolution data measured on a cylindrical $LaNi_5$ metal hydride vessel. The equilibrium pressure used for hydrogen desorption simulations is derived as a function of H/M atomic ratio and temperature based on the experimental data in the literature. The numerical simulation results agree well with experimental data and the 3D desorption model successfully captures key experimental trends during hydrogen desorption process. Both the simulation and experiment display an initial sharp decrease in the temperature mainly caused by relatively slow heat supply rate from the vessel external wall. On the other hand, the effect of heat supply becomes influential at the latter stages, leading to smooth increase in the vessel temperature in both simulation and experiment. This numerical study provides the fundamental understanding of detailed heat and mass transfer phenomena during hydrogen desorption process and further indicates that efficient design of storage vessel and heating system is critical to achieve fast hydrogen discharging performance.

• 한국지반신소재학회논문집
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• 제17권1호
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• pp.55-64
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• 2018

본 연구에서는 최근 도심지에서 발생하고 있는 지반함몰에 대하여 팽창재료를 이용한 긴급복구공법을 적용하고 이러한 공법의 적합성을 수치해석적으로 판단하고자 한다. 수치해석에 적용된 팽창재료의 특성을 평가하기 위하여 실내실험을 수행하였다. 실험으로 구한 팽창특성을 반영하여 다양한 공동 형상(직사각형 단면을 가지는 공동에 대하여 다양한 높이와 폭 조합)에 대하여 팽창재료를 적용하였을 경우 팽창재료 및 지반 거동을 평가하였다. 해석 결과, 공동의 상단과 하단의 연직변위는 공동의 높이보다는 공동의 폭에 큰 영향을 받으며, 공동 측면부의 수평변위는 공동 폭 보다는 공동의 높이의 영향을 많이 받는 것으로 나타났다. 또한, 팽창압이 작용하였을 경우 도로상부 표층의 수직변위량은 공동의 높이보다는 공동의 폭에 큰 영향을 받는 것을 확인할 수 있었다.

• 수산해양기술연구
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• 제37권1호
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• pp.1-8
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• 2001

This study deals with the experimental and numerical investigations to design the high performance otter board. Experiment was carried out to determine the most effective slot size of single-slot cambered otter board in the circulation water channel of BAEK KYUNG IND. Co. LTD. Numerical analysis was done by the commercial CFD code, FLUENT, to provide some valuable physical interpretations and finally to design the otter board section by numerical method. The major results are as follows ; 1. In experiment, the maximum lift and drag coefficients of simple cambered type otterboard were 1.41, 0.55, respectively, at the angle of attack $28^\circ$, while those of slot one with slot size 0.02C (C denotes the chord length) were 1.72, 0.42 at the angle of attack $24^\circ$. 2. The hydrodynamic characteristics depending upon slot size shows the greatest at 0.02C of the slot size. 3. Numerical results well visualized the streamlines, pressure fields, and speed vectors of a simple cambered and slot cambered otter board with slot size 0.02C. The slot cambered one with slot size 0.02C was shown that pressure field was distributed moderately on front and back side of otter board. And, the delay and decrease of separation were favorably achieved by flow through slot. 4. Computed result on the pattern of hydrodynamic field and the values of $C_L$ and $C_D$ by the commercial CFD code, FLUENT, show almost the same as those of the experimental result.

• 한국환경과학회지
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• 제26권4호
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• pp.493-507
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• 2017

Since the late 20th century, the urbanization in Korea has been rapidly increasing, especially in major cities like Seoul, as a result of industrialization. One of the aspects of urbanization is coating the surfaces with impervious concrete or asphalt that water cannot penetrate. In addition, various urban, such as urban heat islands, which also have a great impact on the urban environment, occur within the cities. Therefore, the urban environment is gradually becoming hot and dry, and the need for more urban parks to compensate for these negative impacts is growing. Thus, several numerical studies have been conducted to assess these problems using coupled Numerical Weather Prediction (NWP) and Computational Fluid Dynamics (CFD). In this study, an experiment was conducted to determine the accuracy of the area of the input field using Weather Research and Forecasting (WRF) model, and applying the more accurate input field to a numerical simulation using ENVI-met, in order to investigate the effect of urban parks on the thermal comfort. The results showed that an input field with a larger area is more accurate than that with a smaller area, because the surrounding terrain and cities are considered in details in the experiment with the larger area. Subsequently, the more accurate input field was used in ENVI-met, and the results of this simulation showed that the presence of the urban park increased the thermal comfort and improved the humidity conditions.

• 한국주조공학회지
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• 제27권4호
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• pp.153-158
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• 2007

Molten metal flow in vacuum die casting was characterized by a numerical analysis. The VOF method was used to simulate the filling behaviors of molten metal during filling process. The various vacuum degrees of no vacuum(760 mmHg), 650, 500, 250 and 60mmHg were artificially applied in cavity. And the filling behaviors of molten metal with the applied vacuum conditions were simulated and compared with those of experiment. The results showed that molten metal was partially filled into cavity when vacuum was applied and the filling length of molten metal in cavity was increased with increasing applied reduced pressure in cavity. Also, the simulated filling behaviors of molten metal were apparently similar to those of experiment, indicating the numerical analysis developed in this study was highly effective. Through the result of fluid flow simulation, both relation equations of filling length and filling velocity with the variation of pressure conditions in cavity were calculated respectively and the internal gas contents of casting was significantly reduced by the modification of vacuum gate system.