• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.315-323
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• 2009

Pressure oscillations triggered by the unstable interaction of dynamic flow features of the hydraulic turbine with the hydraulic plant system - including the electrical design - can at times reach significant levels and could lead to damage of plant components or could reduce component lifetime significantly. Such a problem can arise for overload as well as for part load operation of the turbine. This paper discusses an approach to analyze the overload high pressure oscillation problem using computational fluid dynamic (CFD) modeling of the hydraulic machine combined with a network modeling technique of the hydraulic system. The key factor in this analysis is the determination of the overload vortex rope volume occurring within the turbine under the runner which is acting as an active element in the system. Two different modeling techniques to compute the flow field downstream of the runner will be presented in this paper. As a first approach, single phase flow simulations are used to evaluate the vortex rope volume before moving to more sophisticated modeling which incorporates two phase flow calculations employing cavitation modeling. The influence of these different modeling strategies on the simulated plant behavior will be discussed.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.2
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• pp.177-184
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• 2013

This study analyzed the hydraulic characteristics of a venturi flume with a circular cone using a 3-D numerical model which uses RANS(Reynolds-Averaged Navier-Stokes Equation) as the governing equation. The venturi flume with the circular cone efficiently measures the discharge in the low-flow to high-flow range and offers the advantage of accurate discharge measurements in the case of a low flow. With no influence of the tail-water depth, the stage-discharge relationship and the flow behaviors were analyzed to verify the numerical simulation results. Additionally, this study reviewed the effect of the tail-water depth on the flow. The stage-discharge relationship resulting from a numerical simulation in the absence of an effect by the tail-water depth showed a maximum margin of error of 4 % in comparison to the result of a hydraulic experiment. The simulation results reproduced the overall flow behaviors observed in the hydraulic experiment well. The flow starts to become influenced by the tail-water depth when the ratio of the tail-water depth to the total head exceeds approximately 0.7. As the ratio increases, the effect on the flow tends to grow dramatically. As shown in this study, a numerical simulation is effective for identifying the stage-discharge relationship of a venturi flume with various types of venturi bodies, including a venturi flume with a circular cone.

• The Journal of Engineering Geology
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• v.11 no.2
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• pp.141-152
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• 2001

The waterway tunnel zone (length 1,484m) in the Hyeonseo-myeon area that is a part of Yeongcheon dam waterway tunnel has been studied to characterize the relationship between groundwater inflow into the waterway tunnel and hydrogeologic characteristics. The effects of sandstone thickness in the tunnel section. fracture density, fracture aperture and spacing, fault zone width and hydraulic conductivity on the early inflow (inflow prior to the lining and grouting) are investigated. The relationship between fracture density and hydraulic conductivity is also considered. The result of the study suggests that fault zone width has the greatest effect on groundwater inflow into the tunnel, and sandstone thickness, hydraulic conductivity and fracture density in order shows an influence on the inflow.

• Journal of Aerospace System Engineering
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• v.12 no.5
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• pp.54-68
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• 2018

The objective of this study is to analyze the effect of dynamic characteristics of the check valve applied to the small piezoelectric-hydraulic pumps on flow rate formation. The flow rate of the piezoelectric-hydraulic pump is a key factor in the formation of the load pressure to operate the brake system. At this time, the natural frequency of the check valve operating in the fluid has a great influence on the formulation of the flow rate of the piezoelectric-hydraulic pump. In addition, the natural frequency of the check valve is affected by the gap between the check valve and the pump seat. In this study, the natural frequency of the check valve according to the gap between the check valve and the pump seat was calculated through the fluid-structure interaction analysis. The flow rate obtained from the simulation result was verified by comparing it with the result from the flow rate experiment using the developed piezoelectric-hydraulic pump.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1359-1360
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• 2013

• Advances in concrete construction
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• v.6 no.1
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• pp.15-28
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• 2018

In the present investigation, influence of various material parameters on the cavitation erosion resistance of concrete was investigated on the basis of laboratory experiments. As there is no well-established laboratory test method for evaluating the cavitation resistance of concrete, a test set up called 'cavitation jet' was specially established in the present study in order to simulate the cavitation phenomenon experienced in the hydraulic structures. Various mixtures of concrete were designed by varying the grade of concrete, type and quantity of pozzolana, type of aggregates and cement type to develop good cavitation resistant concrete constructed using marginal aggregates. Three types of aggregates having three different Los Angeles abrasion values (less than 30%, between 30% and 50% and more than 50%) were employed in this study. To evaluate the cavitation resistance a total of 60 cylindrical specimens and 60 companion cubes were tested in the laboratory respectively. The results indicate that cavitation resistance of concrete degrades significantly as the L.A. abrasion value of aggregates goes beyond the 30% value. Incorporation of pozzolanic admixtures was seemed to be beneficial to enhance the cavitation resistance of concrete. Influence of other material parameters on the cavitation resistance of concrete was also noted and important observations have been made in the paper.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.88-94
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• 2003

In recent, as Republic of Korea has been interested in environmental problem increasingly and became a member of many organizations or institutions related to environmental preservation such as a Ramsar convention, fundamental and completed methods to prevent ground water's drying up and leakage in tunnel excavation are requested. In this paper, we have studied the anticipated problems by tunnel excavation under the wetland and described the effective designed method to maintain the wetland's ecosystem environment. To accomplish this purpose, firstly, we investigated the wetland's ecosystem, ground's hydraulic properties and analysed the foreign similar case for tunnel excavation near the wetland. And by numerical analysis, we analyzed the runoff and infiltration quantity of water and hydraulic behaviour properties by saturation and unsaturation concept in rock mass and wetland. Finally, we established the effective countermeasure to minimize the ecosystem's bad influence by tunnel excavation.

• Journal of Korean Society of Water and Wastewater
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• v.10 no.4
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• pp.119-126
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• 1996

Influence factors and efficiency characteristics for treatment of wastewater containing phenol were studied with using Pseudomonas sp. B3. It took 130 hours to remove phenol, when only activated sludge of terminal disposal palnt of sewage was innoculated in batch culture, but it was required just 36 hours, when bacteria degrading phenol and activated sludge were simultaneously innoculated. If only phenol an carbon source was used, it necessary 36 hours for biodegradation of phenol, while glucose was added to medium, it took 73 hours. It was revealed as excellent effluent and SVI, when the F/M ratio, COD and phenol concentration were 53mg/l and 1.2mg/l, respectively, and optimum F/M ratio was revealed 0.31. The reactor were seriously shocked as reducing hydraulic retention time at constant phenol concentration more than increasing phenol concentration at constant hydraulic retention time, when volumetric loading rate was increased to $0.8kg\;phenol/m^3{\codt}d$ from $1.6kg\;phenol/m^3{\codt}d$. And also the effluent phenol concentration was 34mg/l after starting 12 hours of shocking and reactor was recovered as steady state after 65 hours of changing in the former test. Although the effluent phenol concentration was maximum value with 12mg/l after starting 20 hours of shocking and reactor was recovered as steady state after 54 hours of changing in the later test.

• The KSFM Journal of Fluid Machinery
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• v.18 no.1
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• pp.20-28
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• 2015

The pump-turbine impeller is the key component of pumped storage power plant. Current design methods of pump-turbine impeller are private and protected from public viewing. Generally, the design proceeds in two steps: the initial hydraulic design and optimization design to achieve a balanced performance between pump mode and turbine mode. In this study, the 3D inverse design method is used for the initial hydraulic impeller design. However, due to the special demand of high performance in both pump and reverse mode, the design method is insufficient. This study is carried out by modifying the geometrical parameters of the blade which have great influence and need special consideration in obtaining the high performance on the both modes, such as blade shape type at low pressure side (inlet of pump mode, outlet of turbine mode) and the blade lean at blade high pressure side (outlet of pump mode, inlet of turbine mode). The influence of the geometrical parameters on the performance characteristic is evaluated by CFD analysis which presents the efficiency and internal flow results. After these investigations of the geometrical parameters, the criteria of designing pump-turbine impeller blade low and high sides shape is achieved.