• 전자공학회논문지B
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• 제31B권8호
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• pp.74-86
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• 1994

In this paper a hierarchical stereo matching algorithm to obtain the disparity in wavelet transformed domain by using locally adaptive window and weights is proposed. The pyramidal structure obtained by wavelet transform is used to solve the loss of information which the conventional Gaussian or Laplacian pyramid have. The wavelet transformed images are decomposed into the blurred image the horizontal edges the vertical edges and the diagonal edges. The similarity between each wavelet channel of left and right image determines the relative importance of each primitive and make the algorithm perform the area-based and feature-based matching adaptively. The wavelet transform can extract the features that have the dense resolution as well as can avoid the duplication or loss of information. Meanwhile the variable window that needs to obtain precise and stable estimation of correspondense is decided adaptively from the disparities estimated in coarse resolution and LL(low-low) channel of wavelet transformed stereo image. Also a new relaxation algorithm that can reduce the false match without the blurring of the disparity edge is proposed. The experimental results for various images show that the proposed algorithm has good perfpormance even if the images used in experiments have the unfavorable conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2094-2099
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• 2004

An experimental study on heat transfer characteristics near the critical pressure has been performed with an internally-heated vertical annular channel cooled by R-134a fluid. Two series of tests have been completed: (a) steady-state critical heat flux (CHF) and (b) heat transfer tests for pressure reduction transients through the critical pressure. In the present experimental range, the steady-state CHF decreases with the increase of the system pressure For a fixed inlet mass flux and subcooling, the CHF falls sharply at about 3.8 MPa and shows a trend toward converging to zero as the pressure approaches the critical point of 4.059 MPa. The CHF phenomenon near the critical pressure does not lead to an abrupt temperature rise of the heated wall because the CHF occurred at remarkably low power levels. In the pressure reduction transient experiments, as soon as the pressure passed through the critical pressure, the wall temperatures rise rapidly up to a very high value due to the occurrence of the departure from nucleate boiling. The wall temperature reaches a maximum at the saturation point of the outlet temperature, then tends to decrease gradually.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1237-1242
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• 2004

In this study, single-phase heat transfer experiments were conducted with oil cooler with offset strip fin using water. An experimental water loop has been developed to measure the single-phase heat transfer coefficient in a vertical oil cooler. Downflow of hot water in one channel receives heal from the cold water upflow of water in the other channel. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the on cooler with offset strip fin remains turbulent. The present data show that the heat transfer coefficient increases with the Reynolds number. Based. On the present data, empirical correlation of the heat transfer coefficient was proposed. Also, performance prediction analysis for oil cooler were executed and compared with experiments. ${\varepsilon}-NTU$ method was used in this prediction program. Independent variables are flow rates and inlet temperature. Compared with experimental data, the accuracy of the program is within the error bounds of ${\pm}5$% in the heat transfer rate.

• Ecology and Resilient Infrastructure
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• 제2권2호
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• pp.161-166
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• 2015

최근 생태하천 복원 사업용으로 개발된 호안 공법에 대한 수리학적 설계기준이 부적절하여 이 공법이 적용된 하천에서 홍수기에 큰 경제적 손실을 유발하고 있다. 본 연구에서는 생태복원용으로 개발된 무독성 호안 블록을 실규모 수로에 설치하여 최고 유량 $3.0m^3/s$, 최고 유속 3.0 m/s에서 수리적 안정성을 평가하였다. 설치된 무독성 호안 블록은 실험 조건에서 상하 ${\pm}3mm$ 정도로 미미하게 이동하였다. 그러므로 실험에 적용한 무독성 호안 블록은 고유속에서 대규모 이동, 블록 파괴, 침상 침하 등이 나타나지 않는 것으로 보아 충분한 안정성을 확보한 것으로 판단되었다.

• 한국해양환경ㆍ에너지학회지
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• 제18권4호
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• pp.274-281
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• 2015

국내 연안에 위치해 있는 화력 및 원자력 발전소는 발전시설 냉각을 위해 해수를 사용한다. 입구를 통해 배출되는 온배수는 유량이 상당하여 입구 근처에 큰 운동에너지가 존재한다. 이러한 제한된 입구에서 빠른 흐름이 존재하는 제트류 영역에 설치된 수직축 터빈의 성능을 수치적으로 조사하였다. 제트류 영역에서 입구와 터빈간 거리, 입구 직경과 수직축 터빈의 직경에 따른 성능 변화를 TSR=3.0에서 조사하였다. 또한, 입구가 1개인 경우와 2개인 경우에 대해 직경이 다른 터빈을 배치하여 성능 및 발전량을 비교하였다. 입구가 1개인 경우 입구로부터 터빈과의 거리가 증가함에 따라 터빈 효율이 감소함을 알 수 있었고, 터빈 직경과 입구 직경이 동일할 때 효율이 가장 좋은 것을 알 수 있었다. 입구가 2개인 경우는 효율 및 총 발전량을 고려하여 입구와 동일한 크기의 터빈을 각각 배치하는 것이 좋은 것을 확인하였다. 본 연구는 방수로 입구 전방에 설치된 수직축 터빈을 개념적으로 설계하는데 활용될 수 있을 것으로 기대된다.

• 대한토목학회논문집
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• 제29권5B호
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• pp.473-482
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• 2009

본 연구에서는 대부분이 수조실험에 의한 추정되어 온 해중의 방파제나 호안 등의 연직벽체에 작용하는 undular 및 turbulent bore에 의한 단파파력을 수치적으로 추정하기 위하여 Navier-Stokes운동방정식에 수면형상의 추적에 VOF법(Hirt and Nichols, 1981)을 채용하고 있는 CADMAS-SURF(CDIT, 2001)를 적용한다. 적용에서는 소스코드를 본 연구의 목적에 부합하도록 일부 수정하였다. 얻어진 원수치데이터에는 급격한 파력의 증감을 나타내는 스파이크현상이 강하게 표현되었으며, 이에 수치필터를 적용하여 5Hz 이상의 고주파수성분을 필터링하였다. 수치해석결과의 신뢰성을 확보하기 위하여 Matsutomi(1991) 및 Ramsden(1996)의 수조실험결과와 비교 검토하였으며, 이로부터 매우 좋은 일치성과 유용성을 확인할수 있었고, 단파성지진해일의 작용하에 있는 구조물의 설계에 도입될 수 있을 것으로 판단된다. 그리고, 본 2차원수조내에서 단파의 변형을 수위의 시 공간변화로부터 추정함과 동시에 전파속도의 변화특성을 나타내었다. 단파의 전파속도는 전파과정에서 변화되는 것을 확인할 수 있었다.

• 한국해양공학회지
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• 제26권4호
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• pp.37-41
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• 2012

Due to global warming, the need to secure alternative resources has become more important nationally. Because of the very strong current on the west coast, with a tidal range of up to 10 m, there are many suitable sites for the application of TCP (tidal current power) in Korea. In the southwest region, a strong current is created in the narrow channels between the numerous islands. A rotor is an essential component that can convert tidal current energy into rotational energy to generate electricity. The design optimization of a rotor is very important to maximize the power production. The performance of a rotor can be determined using various parameters, including the number of blades, shape, sectional size, diameter, etc. There are many offshore jetties and piers with high current velocities. Thus, a VAT (vertical axis turbine) system, which can generate power regardless of flow direction changes, could be effectively applied to cylindrical structures. A VAT system could give an advantage to a caisson-type breakwater because it allows water to circulate well. This paper introduces a multi-layer vertical axis tidal current power system. A Savonius turbine was designed, and a performance analysis was carried out using CFD. A physical model was also demonstrated in CWC, and the results are compared with CFD.

• 대한지하수환경학회지
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• 제5권2호
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• pp.101-109
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• 1998

암반대수층의 수리적 특성은 지하수의 통로가 되는 지질구조에 의해서 크게 좌우된다. 본 연구에서는 수직 지질구조와 관련된 일차원 흐름의 이론들에 대해서 논하였다. 그리고, 경북 영일군 대송면 옥명리에서 행한 두 번의 양수시험(양수시험 1과 양수시험 2)에 대해서, 프락탈 모델을 적용하여 이 지역 수리 특성을 분석하였다. 양수시험분석에 의하면, 양수시험 1(양수정 : D9호공, 관측정 : C3호공과 D7호공)의 시험공 주변은 무한한 길이의 그리고 무한소의 폭을 가지는 수직 지질구조에 의해서 지배되는 일차원 흐름으로 대표되나, 양수시험2의 양수정(D10호공) 주변은 이차원에 가까운 흐름(1.9∼2차원)을 보인다. 이와 같이, 균열암반대수층의 특징은 공간적으로 또는 시간적으로 유동 차원이 달라지는 경우가 많다.

• 한국정밀공학회지
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• 제29권2호
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• pp.214-221
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• 2012

Recently, the biochip which is a prime representation of NT, IT, BT, as an example of convergence technology, has been frequently mentioned. With the recent rapid advance in biotechnology, these compact devices, such as lab-on-a-chip or u-TAS, have been developed, and more research is needed. These compact devices typically use the micro-channel in order to shed or detach and mix a variety of materials. Specially, in micro-fluidic systems, a mixer is necessary to produce a mixture because only laminar flow occurs at a low-Reynolds number. To solve this problem, HVM a micromixer that induces a horizontal and vertical multi-mixing flow motion, is proposed. The mixing performance was analyzed and verified by optimizing the shape through the CFD analysis and evaluating the structural analysis and the soundness with material properties that are obtained through the basic experiment.

• 대한조선학회논문집
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• 제59권2호
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• pp.64-71
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• 2022

In this paper, we simulate the collision of a solitary wave on a vertical wall in a uniform water channel and investigate the effect of damping on the amplitude attenuation. In order to take into account the damping effect, we introduce the Stokes damping whose dissipation is dependent on the velocity of wave motion on the surface of a thin layer of oil. That is, we use the improved Boussinesq equation with Stokes damping to describe the damped wave motion. Our work mainly focuses on the amplitude attenuation of a propagating solitary wave, which may depend on the Stokes damping together with the initial position and initial amplitude of the wave. We utilize the method of images and a powerful numerical tool (functional iteration method) for solving the improved Boussinesq equation, yielding an effective numerical simulation. This enables us to find the amplitudes of the incident wave and reflected one, whose ratio is a measure of the (wave) amplitude attenuation. Accordingly, we have shown that the reflection of a solitary wave by a vertical wall is dependent on not only the initial amplitude and position of a solitary but the Stokes damping.