• Journal of Korea Water Resources Association
• /
• v.44 no.2
• /
• pp.109-123
• /
• 2011

In this study, 2D finite volume model, which can apply to the mixed meshes that is effective to treat the complicated topography such as a natural river, is developed. To do so, an algorithm for finding the neighbouring cell of a computational cell is introduced, and fluxes are computed using the HLLC approximate Riemann solver at each interface between a computational cell and it's neighbouring cells. Moreover, in order to numerically treat the bed slope which has important effect on the balance between flux gradients and sourte terms, different formula to compute the bed slope for rectangular and triangular mesh are applied. The developed model is applied to analyze dam-break in an experimental channel with $90^{\circ}$ bend and Malpasset dam-break in France. The two cases consist of mixed meshes and the suggested method is validated for the experimental channel and natural channel by comparison with the experimental data, field data and computed results.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.7
• /
• pp.751-756
• /
• 2014

The dynamic behavior of numerous grains interacting with each other can be easily observed. In this study, this dynamic behavior was analyzed based on the contact between numerous grains. The discrete element method was used for analyzing the dynamic behavior of each particle and the neighboring-cell algorithm was employed for detecting their contact. The Hertzian and tangential sliding friction contact models were used for calculating the contact force acting between the particles. A GPU-based parallel program was developed for conducting the computer simulation and calculating the numerous contacts. The dam break experiment was performed to verify the simulation results. The reliability of the program was verified by comparing the results of the simulation with those of the experiment.

• Journal of the Society of Naval Architects of Korea
• /
• v.55 no.1
• /
• pp.56-65
• /
• 2018

Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

• Journal of Korea Water Resources Association
• /
• v.46 no.2
• /
• pp.139-153
• /
• 2013

For analyzing shallow-water flows over the uneven bottom, the HLLL scheme and the divergence form for bed slope source term (DFB) technique, respectively were applied to the flux gradient and the bottom gradient source terms in a finite-volume model for the shallow water equations. And also the model incorporated the volume/free-surface relationship (VFR) to consider the partially submerged cells (PSC). It was identified that a simpler version of the weighted surface-depth gradient method in the MUSCL was equivalent to the original one in the accuracy for 1D steady flows. It was verified that the flux gradient term and the bottom gradient source term were well-balanced exactly by the VFR for the 1D PSC. The VFR for the triangular PSC settled the problem which the governing equations were not well-balanced by the DFB technique for the 2D PSC. There were good agreements in simulations and experiments for 2D dam-break flows over a triangular sill and a round bump. In addition, the partial dam-break flow was successfully simulated for flooding of roughnesses in an irregular bottom as well as a sloping one. Therefore, this model is expected to be applied to the real river with uneven topography.

• Journal of Korea Water Resources Association
• /
• v.31 no.3
• /
• pp.279-290
• /
• 1998

The height and speed of the shock wave are critical data in flood-control operations or in the design of channel walls and bridges along rivers with high flow velocities. Therefore, a numerical model is needed for simulating flow discontinuity over a wide range of conditions. In this study, a governing equation. As a Riemann solver Roe(1981)'s one is used. The model employs the modified MUSCL for handling the unstructured grids in this research. this model that adopts the explicit tradditional twl dimmensional dam break problems, two hydraulic dam break model is simulations, and a steady state simulation in a curved channel. Conclusions of this research are as follows : 1) the finite volume method can be combined with the Godonov-type method that is useful for modeling shocks. Hence, the finite volume method is suitable for modeling shocks. 2) The finite volume model combined with the modified MUSCL is successful in modeling shock. Therefore, modified MUSCL is proved to be valid.

• Journal of Korea Water Resources Association
• /
• v.56 no.7
• /
• pp.431-438
• /
• 2023

Many shorelines are facing the beach erosion. Considering the climate change and the increment of coastal population, the erosion problem could be accelerated. To address this issue, developing a sediment transport model for rapidly predicting terrain change is crucial. In this study, a sediment transport model based on GPU parallel arithmetic was introduced, and it was supposed to simulate the terrain change well with a higher computing speed compared to the CPU based model. We also aim to investigate the model performance and the GPU computational efficiency. We applied several dam break cases to verified model, and we found that the simulated results were close to the observed results. The computational efficiency of GPU was defined by comparing operation time of CPU based model, and it showed that the GPU based model were more efficient than the CPU based model.

• Journal of Korea Water Resources Association
• /
• v.49 no.2
• /
• pp.121-132
• /
• 2016

The DAMBRK is applied to Janghyeon and Dongmak reservoirs in Namdaecheon basin, where two reservoirs were failed due to Typhoon Rusa in 2002. Relaxation scheme is added to DAMBRK to consider the tributary cross-section because two reservoirs are in tributary valleys. In addition, this study suggests the method to utilize the reservoir breach formation time of ASDSO (2005) and empirical formulas for peak break outflow from dam to reduce the uncertainty of reservoir breach formulation time. The single break of Janghyeon reservoir and consecutive break of Janghyeon and Dongmak reservoirs with the suggested method are considered. While the breach discharge from reservoirs rushes down, the discharge and water surface elevation along the river are predicted, and the predictions show the attenuation phenomena of reservoir break floodwave. The applicability of the model is validated by comparing the predicted height with field surveyed data, and showing good agreements between predictions and measurements.

• Korean Journal of Hydrosciences
• /
• v.8
• /
• pp.31-40
• /
• 1997

Flow carrying capacity of water distribution systems is getting reduced by deterioration of pipes in the systems. The objective of this paper is to present a managerial decision-making model for the rehabilitation of water distribution systems with a mininum cost. The decisions made by the model also satisfy the requirements for discharge and pressure at demanding nodes in the systems. Replacement cost, pipe break repair cost, and pumping cost are considered in the economic evaluation of the decision along with the break rate and the interest rate to determine the optimal replacement time for each pipe. Then, the hydraulic integrity of the water distribution system is checked for the decision by a pipe network simulator, KYPIPE, if discharge and pressure requirements are satisfied. In case the system does not satisfy the hydraulic requirements, the decision made for the optimal replacement time is revised until the requirments are satisfied. The model is well applied to an existing water distribution system, the Seoul Metropolitan Water Supply System (1st Phase). The results show that the decisions for the replacement time determined by the economic analysis are accepted as optimal and hydraulic integrity of the system is in good condition.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2010.05a
• /
• pp.1846-1851
• /
• 2010

댐붕괴 모델링에 관한 연구가 활성화된 시기는 미국 Baldwin Hills 댐(1964)과 Lower Van Norman(San Fernando) 댐(1971) 붕괴 사고 이후이며 1970년대 발생한 Buffalo Creek 댐(서부 버지니아, 1972), Teton 댐(아이다호, 1976), Laurel Run 댐/Sandy Run 댐(펜실바니아, 1977), Kelly Barnes 댐(조지아, 1977) 붕괴 사고로 인해 미국 댐 안전 관리 프로그램의 포괄적 재검토의 필요성이 제기되었다. 국내에서도 연천댐 붕괴(1996년)와 장현저수지와 동막저수지의 붕괴(2002년)로 하류에 위치한 가옥 및 농경지 침수로 인해 재산피해가 발생한 바 있으며, 2005년 비상대처계획 수립을 의무화하는 제도가 도입되었다. 오늘날 댐 붕괴와 붕괴로 인한 유출 수문곡선을 분석하는데 이용 가능한 수많은 도구들이 존재하고 있다. 가장 잘 알려져 있으며 가장 널리 이용되는 모형은 NWS Dam-Break Flood Forecasting Model(DAMBRK; Fread, 1977)이며 국내 댐 저수지 비상대처계획 수립을 위해 많이 이용되고 있다. DAMBRK 모형의 입력자료는 붕괴지속시간, 결괴부측면경사, 최종결괴부바닥표고, 댐붕괴시작수위 등이 요구되며, 이 중 결괴형성과정에 관련된 매개변수의 선정을 위해서는 댐붕괴 사례연구 자료가 활용되고 있다. 모형으로부터 도출된 붕괴유출수문곡선에 대한 적정성 평가는 과거 경험, 공학적 판단, 첨두유량 예측식에 의해 수행되고 있으며 가장 객관적인 기준이라 판단되는 첨두유출량 예측식은 사례연구 자료의 부족으로 인해 높은 불확실성을 안고 있다. 본 연구는 최근까지 개발된 댐결괴 첨두유출량 예측식을 기반으로 국내 건설된 댐의 대다수를 차지하는 필댐에 대해 댐높이, 댐형식별로 예측식의 적정성을 평가하였다.

• Journal of Korean Society on Water Environment
• /
• v.22 no.3
• /
• pp.521-526
• /
• 2006

We have studied the possibility of removing Anabaena macrospora by injecting copper sulfate ($CuSO_4{\cdot}5H_2O$) into the raw water of a drinking water purification plant. Anabaena macrospora caused the unpleasant geosmin odor of drinking water in August 2001. The cell break-point of A. macrospora was 0.3 mg/L of $CuSO_4$. We were able to reduce the standing crops of A. macrospora effectively because $CuSO_4$ could break A. macrospora selectively. Because 0.3 mg/L of $CuSO_4$ could break both cells and akinetes, it reduced the possibility of a recurrent problem for them to meet a favorable condition. When $CuSO_4$ was injected in the early growth phase of algae and the mixing intensity was high, A. macrospora could be removed most effectively. The odor caused by A. macrospora was sustained for a while without any sudden change of environmental condition. Therefore, we hope that it could shorten the period of obstacle by injecting the optimal amount of 0.3 mg/L of $CuSO_4$. The water quality, alkalinity, conductivity, hardness and pH didn't changed by the injection of $CuSO_4$.