Characteristics of the plume formed by the buoyant discharges from the river

김기철,김성보 한국마린엔지니어링학회 2014 한국마린엔지니어링학회지 Vol.38 No.8

Density currents formed by buoyancy discharges from rivers are numerically studied using non-dimensional two layermodel including Coriolis acceleration, bottom stress, interfacial friction. Some typical numbers such as Froude number, densimetricFroude number and Kelvin number are obtained and some characteristic scales are defined as a result of non-dimensionalizationof the governing equations. Besides the Coriolis effect, the configurations of bottom topography, bottom friction coefficient and interfacial friction are foundto significantly affect the propagation of the warm water plume. Frontal position can fastly propagate in the case of large densitydifference between the two layers and small interfacial friction. Left side boundary current is easily formed under the smallinterfacial friction. With large Kelvin number, both right and left side boundary currents are formed. Wave-like disturbancesand eddies are easily formed under the high Froude number.

The linear model for wave generation of a bump

AZIS S. SANI,L.H. WIRYANTO 장전수학회 2019 Proceedings of the Jangjeon mathematical society Vol.22 No.1

A channel with a bump over at bottom will aect the pro- le of the water surface that ows over it. This phenomenon can be modeled by the nondimensional Boussinesq equation. The governing equation used is expressed in variable of speed, elevation, the height of bump and Froude number. Here, we will investigate the dependance of wave formed by a bump on Froude number and dimension of the bump. In this paper, we focus only on the case of supercritical ow or Froude number greater than 1. We will derive the analytical solution for the free surface prole over a bump. From the analytical solution, we conclude that a bump generate waves with 1 peak and 2 dales. The formed peak does not propagate anywhere, but the two dales propagate to the direction of the ow with dierent speed and amplitude. For- ward Time Backward Space (FTBS) method is implemented to solve the equation numerically. The obtained numerical results conrm the analytical solution well.

태백산맥 풍하측 대기 물뜀 발생에 관한 수치 실험

이재헌(Jaeheon Lee),강성락(Song-lak Kang) 한국방재학회 2022 한국방재학회논문집 Vol.22 No.6

태백산맥 풍하측 대기 물뜀에 대한 큰 에디 모사는 온난이상 이류와 음의 와도 대기 역류를 잘 보여주었다. 대기 물뜀은 상층 대기를 하층 대기로 유입한다. 모의된 물뜀 발생은 장애물의 유효 고도와 폭의 함수로 정리될 수 있었다: â > 10에 대해 ĥ ≥ 0.74, 이는 장애물의 고도와 폭으로 정의된 프루드 수로 Fra < 0 .1에 대해 Frh ≤ 1.35에 해당한다. 수치 실험에서, 부력 진동수(N) = 0.009 s-1에 대해 풍상측 평균 바람(U) ≤ 12 ms-1일 때 물뜀이 발생하였다. 물뜀 현상이 발생할 때 풍속은 30분 내외로 급격한 상승을 보였고, 초기 풍속이 강할수록 보다 강한 온난이상과 돌풍이 발생하였다. 본 연구는 산불 발생환경 조성 측면에서 대기 물뜀 현상을 이해하고, 이를 장애물 폭과 장애물 높이를 사용한 프루드 수의 함수로 설명하였다. 결과적으로 대기는 물뜀 현상이 발생할 시 보다 산불에 취약한 대기 환경을 형성할 수 있었고, 프루드 수의 함수로는 대기 물뜀과 관련된 산악파 파쇄가 잘 설명될 수 있었다. Large-eddy simulation of the lee-side hydraulic jump at the downwind side of the Taebaek Mountains demonstrates the advection of a warm anomaly and the atmospheric reverse roller of negative vorticity. The lee-side hydraulic jump entrains the upper-level atmospheric air into the lower-level atmosphere. The simulated lee-side hydraulic jump occurs under the following conditions on the effective height ĥ and width â of an obstacle: ĥ ≥ 0.74 for â > 10, which are equivalent to Frh ≤ 1.35 for Fra < 0 .1, where Frh and Fra are the Froude numbers defined in terms of the height and width of the obstacle, respectively. In detail, the hydraulic jump occurs when the upwind-side mean wind (U) ≤ 12 ms- 1 for the buoyancy frequency (N) = 0.009 s- 1. The wind speed dramatically increases within the 30-minute period when the hydraulic jump occurs. The stronger upwind causes a warmer anomaly and stronger downslope wind gust. This study situates the atmospheric hydraulic jump phenomenon with regard ro wildfire occurrence, and describes it using the Froude number for the width and height of the obstacle. It is shown that a more vulnerable atmospheric environment can be formed when the hydraulic jump occurs, and the wave-breaking of mountain waves related to the hydraulic jump can be predicted by the Froude number.

90도 각도를 갖는 분기수로에서 모형실험결과를 이용한 손실계수 경험식 산정

박인환,성호제,김형준,이동섭 대한토목학회 2017 대한토목학회논문집 Vol.37 No.6

본 연구에서는 분기수로에서 발생되는 에너지손실을 계산하기 위한 손실계수의 경험식을 산정하기 위해 수리모형실험을 수행했다. 수리모형은 유입수로와 90도의 각도를 갖는 두 유출수로로 구성되어 있으며, 유입수로과 유출수로에서 압력수두와 속도수두를 측정하여 분기수로에서 발생되는 에너지손실을 분석했다. 각 측선에서 동수경사선의 변화를 비교한 결과, 수로의 분기점에서 동수경사선이 급격히 하강하여 에너지손실이 분기점에서 발생되었으며, 유량비의 증가에 따라 속도수두의 감소폭이 증가했다. 유량비와 Froude수가 증가함에 따라 유출량이 더 큰 수로에서 수두손실량이 지수적으로 증가하는 결과를 보였으며, 손실계수 또한 증가했다. 반면에, 유출량이 작은 수로에서는 유량비와 Froude수의 증가에 따라 손실계수가 감소하는 결과가 나타났다. 손실계수 계산결과를 이용하여 두 유출수로에서 손실계수 경험식을 제안하였으며, 경험식의 계산오차가 각각 3.91%, 5.19%로 나타났다. 그리고 두 경험식을 이용하여 계산한 총 손실계수를 실험결과와 비교하여 3.62%의 오차가 발생했다. In this study, hydraulic experimental studies were conducted to estimate the empirical formulas of loss coefficient, which is necessary to calculate the energy loss occurred in the dividing channel junction of sewer system. The experimental apparatus was consisted of two outflow conduit with a 90° angle to the inlet conduit, and the pressure and velocity heads are measured to analyze the energy losses inthe branch. The measurements of the hydraulic grade line show that the hydraulic grade line was steeply descended at the dividing point due to the head loss, and the decreasing amount of velocity head increased with the increase of flowrate ratio. The head loss exponentially increased in the outlet with larger runoff as the increase of flowrate ratio and Froude number, and the head loss coefficientalso increased. On the other hands, the head loss coefficients decreased in the outlet with smaller runoff as the increase of the flowrate ratio and Froude number. Using the experimental results, the empirical formulas of loss coefficient was suggested for each outlet, and the error of empirical formula was 3.91 and 5.19%, respectively. Furthermore, the total head loss coefficient calculated by the two empirical formulas was compared with the experimental results, and the error was 3.62%.

Archimedes number를 이용한 장방형 침전지내 수리흐름 평가에 관한 연구

박노석 ( No Suk Park ),이상욱 ( Sang Uk Lee ) 대한상하수도학회 2009 상하수도학회지 Vol.23 No.6

Numerical investigation on the wave interferences of submerged bodies operating near the free surface

Li Dong,Yang Qun,Zhai Lin,Wang Zhen,He Chuan-lin 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

A key factor that governs the wave interferences of a submerged body is the dimensionless Froude number. Computational Fluid Dynamics (CFD) is used to describe the resistance force coefficients and the generated waves of two SUBOFF submarine models. Grid independence studies are performed on two cases, totally and shallowly submerged cases, with four sets of computing meshes. The highest peaks are marked by red points at given wavelengths, a line is fitted to those points with a least-squares approximation, and the half wake angle at multiple Froude numbers is defined between the fitted line and the centerline of the free surface. The results show that when the depth of the target is 1.1D, constructive interferences occur at Fn ¼ 0.3 and 0.5, while destructive interference occurs at Fn ¼ 0.35 with distortion of the waveform. The half wake angle is less than 19.47 because of the interference between the bow and stern wave systems.

하천여울에서 폭기효과에 대한 수리학적 연구

안성식,이상수,김진홍 中央大學校 建設環境硏究所 2002 環境科學硏究 Vol.13 No.2

본 연구에서는 하천 여울에서 폭기 현상에 따른 산소전달 및 수중 용존 산소 증가 현상에 대한 수리학적 특성을 분석하였다. 이를 위해 폭기 효과가 잘 발생되는 여울의 일정 구간을 선정하여 여울 상·하류에서 용존산소의 농도변화를 측정하고, 이를 여울의 흐름 특성 및 하상입자와 관련지어 검토하였다. 분석결과 폭기효과는 흐름의 유속, 유량 및 Froude 수에 비례하여 증가함을 알 수 있었다. 또한 폭기 효과는 하상입자의 모난 부분의 배후에서 보다 더 잘 발생됨을 알 수 있었다. This study presents the hydraulic characteristic in the oxygen transfer and increase of dissolved oxygen due to aeration effect in the riparian riffles. Aeration was found to be proportional to the flow velocity, flow discharge and Froude number. It occurred more frequently in the square-edged gravels rather than in the round-edged ones, and was formed mainly from behind the trailing edge of the square-edged gravels.

Discharge coefficient estimation for rectangular side weir using GEP and GMDH methods

Hussain, Ajmal,Shariq, Ali,Danish, Mohd,Ansari, Mujib A. Techno-Press 2021 Advances in computational design Vol.6 No.2

Flow through the rectangular side weir is a spatially varied type flow with decreasing discharge and used as a flow diversion structure. They are mainly used in the field of hydraulic, irrigation, and environmental engineering for diverting and controlling the flow of water in irrigation-drainage systems, drainage canal systems, and wastewater channels. In this study, gene expression programming and group method of data handling were used to estimate the coefficient of discharge for rectangular side weir under subcritical flow condition. Based on dimensional analysis, the coefficient of the discharge depends on the ratio of the crest height to length, ratio of the width of channel to crest length, ratio of the upstream depth in the channel to crest length and the approach Froude number. The performance of the proposed GMDH and GEP model is based on the coefficient of correlation (0.91), mean absolute percentage error (3.54), average absolute deviation (3.3), root mean square error (0.027) and the coefficient of correlation (0.905), mean absolute percentage error (4.12) average absolute deviation (3.9), root mean square error (0.029), respectively. Finally, the results reveal that GMDH model could provide more satisfactorily estimations as compared to those obtained by traditional regression and GEP models.

논문 : 침전지 추적자 실험의 해석을 위한 Dispersion Number의 적용

김영일 ( Young Il Kim ),박노석 ( No Suk Park ),정남정 ( Nam Jung Jung ),김성수 ( Seong Su Kim ),배병욱 ( Byung Uk Bae ) 대한상하수도학회 2007 상하수도학회지 Vol.21 No.2

Exploring the effects of speed and scale on a ship’s form factor using CFD

Terziev Momchil,Tezdogan Tahsin,Demirel Yigit Kemal,Villa Diego,Mizzi Simon,Incecik Atilla 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

The problem of predicting a ship’s form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship’s speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-ω, k-ω SST, and k-ε models). The results show that at very low speeds (Froude numbers in the range of 0.02–0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.