• Journal of Korea Water Resources Association
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• v.52 no.4
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• pp.255-264
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• 2019

The trapezoidal ribs had been installed in the retaining wall in order to reduce to flood damage in the impingement of mountain rivers. In this study, experiments in open channel with the trapezoidal ribs on sidewall were conducted to evaluate the effect of flow resistance by the trapezoidal shape. The hydraulic flow characteristics according to the flow rates were surveyed where the wall roughness is k-type that dimensionless spacings, ${\lambda}_{nv}$, are 6, 9, and 12. The flow-resistance factors such as roughness and friction coefficients increased generally with increase of the spacing of ribs. In high flow rate the friction coefficient showed the maximum value when ${\lambda}_{nv}$ is 9. Though the trapezoidal ribs has the relatively smaller flow resistance compared to the square ribs, their form drag accounted for mean 62% of the total flow resistance. It was confirmed that the optimal spacing of trapezoidal ribs to maximize the effect of flow resistance as the wall roughness increases are 9 to 12 times of the height of trapezoidal ribs.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.625-631
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• 2011

The passive control of fluid force acting on a square prism near a plane wall was studied by attaching horizontal splitter plate on the corner of the prism. The width of the splitter plate was 10% of the square width. The experiments were performed by measuring of fluid force on the prism and by visualization of the flow field using PIV. The experimental parameters were the attaching position and the space ratios G/B between the prism and wall. The flow between the prism and wall was remarkable and Karman vortex in the wake of the prism was considerable in the space ratio over 0.4. The point of inflection of average lift coefficient and Strouhal number on the prism were represented at the space ratio G/B=0.4 for the prototype prism and G/B=0.6 for the prism having horizontal splitter plate. The drag of the prism was reduced average 4.5% with the space ratios by attaching the horizontal splitter plate at the rear and lower corner on the prism. In this case, the size of the separated region on the upside of the prism was smaller than that of prism without the splitter plate.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.3
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• pp.33-41
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• 1993

양벽면 모두 사각돌출형조도요소가 설치된 동심 이중관내에서 생기는 비대칭 난류유동과 열전달 특성을, 열전달과 마찰계수에 미치는 조도의 합성효과를 조사하기 위해, 연구하였다. 이론해석에서는 한쪽면에 거칠기가 있는 평행평판의 유동에 대한 수정 플란틀 혼합길이(mixing length)이론의 난류 모델을 속도분포와 마찰계수를 구하는데 사용하였다. 최대속도지점에서 안쪽과 바깥쪽의 두 속도형상들은 힘의 평형에 의해 일치시켰다. 그리고 나서, 온도 분포와 열전달 계수를 계산하였다. 속도형성과 마찰계수들의 해석결과는 실험과 매우 잘 일치하였다. 마찰계수와 Nusselt number에 미치는 조도비, 조도에 대한 피치비, 그리고 반경비등과 같은 여러 변수들의 효과들을 조사하였다. 본 연구는 일정의 조도 요소들이 전체적 효율 측면에서 볼때 유리하게 열전달을 향상시킨다는 것을 증명하였다.

• 한국항공운항학회:학술대회논문집
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• 2015.11a
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• pp.35-38
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• 2015

본 연구에서는 스포츠급 경항공기 모형의 공력 특성을 공군사관학교 아음속 풍동에서 측정하였다. 풍동시험은 유속 40m/s에서 이전 모델과 최근 공력성능 향상을 위해 보완된 모델에 대해 비교 실험 수행하였으며, 정확한 데이터를 얻기 위하여 흐름각 효과, 벽면효과, 지지대 간섭효과를 보정하여 공력계수를 산출하였다. 실험 결과, 두 모델의 항력계수와 양력계수가 전체적으로 유사한 경향성을 보이나 고받음각에서의 양력특성의 차이가 발생하였다. 또한 실제 비행 시의 레이놀즈 수 유동을 모사하기 위하여 Trip strip의 영향에 대하여 실험하였다. 그 결과 Trip strip을 부착하였을 경우 항력계수가 증가하고 최소항력받음각이 낮아지는 결과를 획득하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.04a
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• pp.7-7
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• 1999

충돌/유출냉각은 연소실 벽면 등과 같이 열부하가 많이 걸리는 영역에서 고온의 연소가스로부터 표면을 보호하는 막냉각과 더불어 내부에 다공성 판을 설치하여 충돌제트에 의해 내부표면을 냉각시켜 가스터빈엔진의 고온요소의 냉각성능을 극대화시키는 방법 중의 하나이다. 이와 같은 냉각방법을 적용하면 벽면을 충돌제트에 의한 냉각과 함께 냉각유채를 막냉각에 활용함으로써 냉각효율을 극대화할 수 있다. 본 연구에서는 국소적인 값들을 획득하기 용이한 물질전달실험방법의 하나인 나프탈렌 승화법을 이용하여 수직으로 분사되는 충돌제트에 의한 유출판 내면에서의 열/물질전달특성을 분사판(injection plate)과 유출판(effusion plate) 사이의 높이, 분사제트의 속도, 분사홀간의 배열을 변화시켜가며 유출판만이 있는 경우와 비교, 분석하였다. 분사홀과 유출홀의 관 사이의 간격은 0.33d에서 10d까지 변화시켜가며 그 효과를 관찰하였으며, 홀배열 효과를 보기 위하여 2가지 홀배열(staggered array, shifted array)에 대하여 실험하였다. 또한 분사제트의 속도효과를 고찰하기 위하여 분사제트의 Rc$_{d}$=5,000-12,000까지 변화시켜가며 실험을 수행하였다.

• Journal of the Society of Disaster Information
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• v.14 no.2
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• pp.107-114
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• 2018

Purpose : This study is to develop walls using wall recording technology applied on roofs to prevent fire spread in traditional markets. Method : The spray head installed on the developed wall was designed so that the fire does not spread to adjacent buildings after being used for plants. In addition, a spray head was attached to the upper section and some sections for the growth of plants planted on the wall to prevent the spread of fire. Results : These technologies suggested the development of walls that can be installed at the upper level of buildings, such as traditional markets, and separate isolation facilities were not necessary because they are integrated with structures and sprinklers. In addition, sprinklers can perform both the plant spray and fire spread prevention functions. It is believed that this is the only alternative technology proposed in Korea to prevent the spread of fire. Conclusion : In this study, the wall design, designed directly to derive the quantitative performance of the fire spread reduction effect, demonstrated the fire suppression method of the wall system, the durability of the wall itself, and the flame retardability performance.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.261-271
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• 2000

The present study investigated flow dynamics of a two-dimensional abdominal aortic bifurcation model under sinusoidal flow conditions considering wall motion. impedance phase angle(time delay between pressure and flow waveforms), and non-Newtonian fluid using computational fluid dynamics. The wall shear stress showed large variations in the bifurcated region and the wall motion reduced amplitude of wall shear stress significantly. As the impedance phase angle was changed to more negative values, the mean wall shear stress (time-averaged) decreased while the amplitude (oscillatory) of wall shear stress increased. At the curvature site on the outer wall where the mean wall shear stress approached zero. influence of the phase angle was relatively large. The mean wall shear stress decreased by $50\%$ in the $-90^{\circ}$ phase angle (flow wave advanced pressure wave by a quarter period) compared to the $0^{\circ}$ phase angle while the amplitude of wall shear stress increased by $15\%$. Therefore, hypertensive patients who tend to have large negative phase angles become more vulnerable to atherosclerosis according to the low and oscillatory shear stress theory because of the reduced mean and the increased oscillatory wall shear stresses. Non-Newtonian characteristics of fluid substantially increased the mean wall shear stress resulting in a less vulnerable state to atherosclerosis.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.5
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• pp.637-643
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• 2019

Wind tunnel testing for flow-through model is necessary for performance prediction of an aircraft with air-breathing jet engine. Internal drag correction and wall correction are performed to acquire preciser wind tunnel test data. Many test runs are generally required to correct internal drag and wall interference in wind tunnel test. In this study we investigated more effective correction schemes using the response surface method. Even though the number of tests required for these schemes was much smaller than that for conventional methods, the differences between corrections using these schemes and conventional methods were similar level with the uncertainty of measurement except for the data near the boundaries.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.2
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• pp.136-143
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• 1997

직경 비가 0.56인 이중동심관에 내외측모두 매끈한 벽면, 벽면 거칠기를 안측, 외측, 그리고 양측 모두의 4경우에 대한 난류 유동과 열전달특성을 실험과 이론으로 연구하였다. 시간평균속도분포, 마찰계수, 그리고 최대 속도 지점과 전단응력이 0인 지점들을 피토튜브와 X형 열선 풍속계로 측정하였다. 이중동심관내에서 4가지 경우에 따른 사각돌출형 거칠기효과가 난류 유동과 열전달에 미치는 영향을 수정난류모델을 기초로 하여 연구하였다. 직경비, 거칠기 위치, 레이놀즈수, 그리고 프란틀수 등의 여러 변수에 의해서 난류 유동과 열전달을 고찰하였다. 본 연구는 전체적 효율 측면에서 유리하게 열전달율을 향상시킬수 있는 거칠기 구조를 밝혔다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.735-746
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• 1997

A nonlinear low-Reynolds-number k-.epsilon. model of Park and Sung was extended to predict the flows over a step with inclined wall, where a boundary layer flow without separation and a separated and reattaching flow coexist. For a better prediction of the flows, a slight modification was made on the function of the wall damping( $f_{\mu}$) and the model constant ( $C_{{\epsilon}1}$) in the .epsilon.-equation. The model performance was validated by comparing the model predictions with the experiment. It was shown that the flows over a step with inclined wall are simulated successfully with the present model.ent model.