• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.510-520
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• 2019

To investigate the morphology characteristics of air layer in the air cavity, a numerical method with the combination of RANS equations and VOF two-phase-flow model is proposed for a plate with air cavity. Based on the model above, the dynamic and developmental process of air layer in the air cavity is studied. Numerical results indicate that the air layer in the plate's air cavity exhibits the dynamic state of morphology and the wavelength of air layer becomes larger with the increasing speed. The morphology of air layer agrees with the Froude similarity law and the formation of the air layer is not affected by the parameters of the cavity, however, the wave pattern of the air layer is influenced by the parameters of the cavity. The stable air layer under the air cavity is important for the resistance reduction for the air layer drag reduction.

• 한국습지학회지
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• 제15권1호
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• pp.91-103
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• 2013

본 연구에서는 자연친화적인 호안 블록의 현장 적용시 충분한 기술적인 검증과 구조적, 수리학적 안정성 검토 등이 제대로 이루어지지 않고 있는 문제점을 개선하기 위해 생태적 기능을 확보할 수 있는 식생강화를 위한 다공성 소일 블록에 대하여 수리적 거동 변화에 따른 수리학적 안정성을 검토하였다. 대상구간을 선정하여 수치해석 및 수리모형실험을 실시하였으며 수치해석을 위해 1차원 수치해석모형인 HEC-RAS와 2차원 수치해석모형인 RMA-2를 이용하여 1, 2차원 수치해석을 실시하였고, Froude 상사법칙을 적용하여 식생 유, 무에 따른 축척된 수리모형실험을 실시하였다. 수리모형실험의 경우 실험결과에 대한 타당성을 위해 축척된 수리모형실험의 유속 및 소류력 결과를 원형으로 환산하여 1, 2차원 수치해석결과와 동일한 조건하에 비교 검토하였고 그 결과 비교적 일치된 결과가 나타난 것으로 확인되었으며 이에 따른 원형으로 환산된 소류력 결과를 기존 연구결과인 호안의 허용소류력과 비교함으로써 블록의 수리학적 안정성을 제시하였다.

• 대한토목학회논문집
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• 제7권1호
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• pp.11-22
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• 1987

흐름수역(水域)에서 연직상향으로 방류되는 평면부력(平面浮力)?의 거동이 연속방정식(連續方程式), 운동량방정식(運動量方程式) 및 추적물수송식(追跡物輸送式)의 기본방정식을 수치적(數値的)으로 풀음으로서 해석(解析)된다. 난류확산(亂流擴散)에는 Prandtl의 혼합거리이론(混合距離理論)을 도입한 난류수송모형(亂流輸送模型)이 이용된다. 수치해과정(數値解過程)은 기본방정식을 유함수(流凾數)(stream function)식(式)과 골도수송(滑度輸送)(vorticity transport)식을(式) 이용하여 변환(變換)한 후, ?방류속도(放流速度), ?방류구폭(放流口幅) 등(等)으로 표현되는 변수(變數)와 흐름을 지배(支配)하는 무차원매개변수(無次元媒介變數)를 도입하여 무차원화(無次元化)하고 successive under-relaxation을 이용하여 Gauss-Seidal 반복법(反復法)으로 해를(解) 구(求)하는 것이다. 수치실험(數値實驗)은 방류(放流)Froude수(數)가 4~32, 방류속도(放流速度)와 가로흐름속도와의 비로(比) 정의되는 속도비가 8~15 의 범위의 흐름영역(領域)에서 수행되었다. 부력(浮力)?으로 인한 주변(周邊)흐름수역(水域)의 속도변화(速度變化), 온도상승(溫度上昇)범위, 흐름상태 및 골도(滑度)가 조사되었으며, ?의 경로에 대한 속도비와 방류밀도Froude 수의 영향이 또한 조사되었다. ?중심선의 속도, 온도변화, 국부밀도(局部密度)Froude 수(數)의 변화가 계산되며 퍼짐율(spreading rate)과 확산비(擴散比)(dispersion ratio)가 방류밀도(放流密度)Froude 수, 국부밀도(局部密度)Froude 수(數) 및 속도비(速度比)의 항(項)으로 해석되었다. 또한 속도와 온도분포를 상사(相似)(similarity)로 나타낼 수 있음이 밝혀졌으며, Gaussian 분포(分布)를 이용한 적분형해석(積分型解析)(integral type analysis)이 가능한 것으로 사료된다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1217-1224
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• 2014

This paper provides a practical scaling method to solve an old problem for scaling and developing the speed and resistance of a model to full-scale submarine in fully submerged underwater test. In every experimental test in towing tank, water tunnel and wind tunnel, in the first step, the speed of a model should be scaled to the full-scale vessel (ship or submarine). In the second step, the obtained resistance of the model should be developed. For submarine, there are two modes of movement: surface and submerged mode. There is no matter in surface mode because, according to Froude's law, the ratio of speed of the model to the full-scale vessel is proportional to the square root of lengths (length of the model on the length of the vessel). This leads to a reasonable speed and is not so much for the model that is applicable in the laboratory. The main problem is in submerged mode (fully submerged) that there isn't surface wave effect and therefore, Froude's law couldn't be used. Reynold's similarity is actually impossible to implement because it leads to very high speeds of the model that is impossible in a laboratory and inside the water. According to Reynold's similarity, the ratio of speed of the model to the full-scale vessel is proportional to the ratio of the full-scale length to the model length that leads to a too high speed. This paper proves that there is no need for exact Reynold's similarity because after a special Reynolds, resistance coefficient remains constant. Therefore, there is not compulsion for high speeds of the model. For proving this finding, three groups of results are presented: two cases are based on CFD method, and one case is based on the model test in towing tank. All these three results are presented for three different shapes that can show; this finding is independent of the shapes and geometries. For CFD method, Flow Vision software has been used.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1313-1317
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• 2006

In this study, various hydraulic phenomena were analyzed from the dam model experiments and the analyzed results were compared with existing computation results. Sungduk dam model structures were constructed using Froude similarity law by 1:50 scale. From the measurements of hydraulic phenomena at spillway channel, an improvement method was trying to be suggested over shortcoming of existing design plan. The result of model experiment showed no big difference with that of each part's numerical interpretation. Sidewall overflows were observed, as water conveyance occurred due to the linear characteristics of spillways, which raised the necessity for improving the linear forms of spillways. Also, it was judged to be necessary improving load pressure and establishing protective structures at the riverbed grounds of downstream channels.