• Journal of the Korean Geotechnical Society
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• v.31 no.1
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• pp.53-64
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• 2015

This study presents the experimental results of pervious blocks subjected to a series of unique inflow conditions in urban area. The measured properties include the strength, permeability, drainage capacity and runoff, and evaporation for blocks made of two different size of aggregates. Results revealed that the strength satisfies the Korean Standard regardless of aggregate size whereas the immediate runoff occurred for the block with small size aggregate. On the other hand, the block with large aggregates allowed the drainage upon the initial inflow condition, which became hampered to induce the runoff by subsequent inflow. It was attributed to the fact that the capillary water often served as the hydraulic barrier in partially saturated condition. The salient observation indicated that the runoff highly depended on the evaporation and pre-wetting condition as well as the porosity and pore connectivity. The bilinear evaporate rate that makes the degree of saturation vary also had great influence on deterining the time-dependent runoff.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.12
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• pp.1265-1273
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• 2015

A coal handling machine is a type of equipment used for loading coal, the main material in a steam power plant, along a conveyer belt from a ship, and is placed after the driving chain bucket. However, studies on the boom hoisting cylinder, which is a hydraulic system used to control the angle of the boom based on loading location, indicate that domestic models are insufficient, and are thereby often substituted with a foreign product. In this study, a technique for analyzing the contact pressure in a thick-walled cylinder was established by comparing the contact pressure, which is calculated theoretically based on the results obtained from FEM simulation, and by checking whether the working oil is leaking from the boom hoisting cylinder using a v-seal. In addition, the driving motion was simulated according to the strokes of the cylinder, and the structural stability was verified under the maximum output conditions.

• International Journal of Fluid Machinery and Systems
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• v.9 no.2
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• pp.182-193
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• 2016

Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations since they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating directions called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.363-373
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• 2018

The evaluation of Thermo-Hydro-Mechanical (THM) coupling behavior is important for the development of underground space for various purposes. For a high-level radioactive waste repository excavated in a deep underground rock mass, the accurate prediction of the complex THM behavior is essential for the long-term safety and stability assessment. In order to develop reliable THM analysis techniques effectively, an international cooperation project, Development of Coupled models and their Validation against Experiments (DECOVALEX), was carried out. In DECOVALEX-2015 Task B2, the in situ THM experiment that was conducted at Horonobe Underground Research Laboratory(URL) by Japan Atomic Energy Agency (JAEA), was modeled by the research teams from the participating countries. In this study, a THM coupling technique that combined TOUGH2 and FLAC3D was developed and applied to the THM analysis for the in situ experiment, in which rock, buffer, backfill, sand, and heater were installed. With the assistance of an artificial neural network, the boundary conditions for the experiment could be adequately implemented in the modeling. The thermal, hydraulic, and mechanical results from the modeling were compared with the measurements from the in situ THM experiment. The predicted buffer temperature from the THM modelling was about $10^{\circ}C$ higher than measurement near by the overpack. At the other locations far from the overpack, modelling predicted slightly lower temperature than measurement. Even though the magnitude of pressure from the modeling was different from the measurements, the general trends of the variation with time were found to be similar.

• Journal of the Korean Geosynthetics Society
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• v.14 no.4
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• pp.97-104
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• 2015

When carrying out design for soft ground improvement before reclamation of dredged soil, it is very important to appropriately evaluate design parameters such as compression index and undrained strength in order to estimate optimum construction cost. In this study, consolidation and strength parameters were estimated by the samples obtained from the similar reclaimed land. Water content and compression index of dredged soil reclaimed by hydraulic fill method were quite decreased in comparison with those of in-situ conditions at Incheon site. Relationships between compression index(Cc) and water content (wn), and between undrained strength (su) and water content (wn) for dredged soil were obtained by field vane test and oedometer test, respectively. Applicability of Schmertmann correction method (compression index) for low plasticity silty soil was discussed according to comparison with designed and measured settlements.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.213-219
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• 2003

As the 2-D hydraulic experimental results for the submerged rubble-mound structure, we have concerned with their stability/function characteristics of structures by the effects of wave force, scour/deposition at the toe and wave transmission ratio at the lee-side sea. And as to investigate the variation characteristics of wave transmission ratio which depended to a geometrical structure of the submerged breakwater profiles, the critical conditions for the depth of submergence and crest width obviously presented. In summary, there results lead us to the conclusions that the wave control capabilities of submerged breakwaters by the variation of the submergence depth is high about 4 time degrees at the efficiency than the that of crest width. The destruction of covering block at the crest generated at the region which located between maximum damage curve, it maximum damage/failure station from the toe of the structure were 0.2L. As the wave transmission coefficient and the slope of the structure increase, the damage/failure ratio and the maximum scour depth at the toe was extended, respectively. When maximum scour depth happened. The destruction of covering block which located at the toe generated at the front slope destruction. Finally, it was found from the results that the optimization of structure may be obtained by the efficiently decision of the submergence depth and crest width in the permissible range of wave transmission ratio.

• Journal of Environmental Science International
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• v.20 no.5
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• pp.555-564
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• 2011

This study examines the potential restoration of abandoned channels of the Mangyeong River in South Korea. To analyze the morphological changes and equilibrium conditions, a flow duration analysis was performed to obtain the discharge of 255 m3/s with a recurrence interval of 1.5 year. It is a gravel-bed stream with a median bed diameter of 36 mm. The reach-averaged results using HEC-RAS showed that the top width is 244 m, the mean flow depth is 1.11 m, the width/depth ratio is very high at 277, the channel velocity is 1.18 m/s, and the Froude number is also high at 0.42. The hydraulic parameters vary in the vicinity of the three sills which control the bed elevation. The total sediment load is 6,500 tons per day and the equivalent sediment concentration is 240 mg/l. The Engelund-Hansen method was closer to the field measurements than any other method. The bed material coarser than 33 mm will not move. The methods of Julien-Wargadalam and Lacey gave an equilibrium channel width of 83 m and 77 m respectively, which demonstrates that the Mangyeong River is currently very wide and shallow. The planform geometry for the Mangyeong River is definitely straight with a sinuosity as low as 1.03. The thalweg and mean bed elevation profiles were analyzed using field measurements in 1976, 1993 and 2009. The measured profiles indicated that the channel has degraded about 2 m since 1976. The coarse gravel material and large width-depth ratio increase the stability of the bed material in this reach.

• The KSFM Journal of Fluid Machinery
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• v.16 no.1
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• pp.56-60
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• 2013

Non-conventional oil resources such as shale gas are becoming increasingly important and have drawn the attention of several major oil companies all over the world. Nevertheless, the market-changing growth of shale gas production in recent years has resulted in the emergence of environmental and water management challenges. This is because the water used in the hydraulic fracturing process contains large amount of pollutants including ions, organics, and particles. Accordingly, the treatment of this flowback water from shale gas plant is regarded as one of the key technologies. In this study, we examined the feasibility of membrane distillation as a treatment technology for the water from shale gas plants. Direct contact membrane distillation (DCMD) is a thermally-driven process based on a vaper pressure gradient across a hydrophobic membrane, allowing the treatment of feed waters containing high concentration of ions. Experiments were carried out put in the lab-scale under various conditions such as membrane types, temperature difference, flow rate and so on. Synthetic feed water was prepared and used based on the data from literature. The results indicated that DCMD is suitable for treating not only low-range flowback water but also high-range flowback water. Based on the theoretical calculation, DCMD could have over 80% of recovery. Nevertheless, organic pollutants such as oil and surfactant were identified as serious barriers for the application of MD. Further works will be required to develop the optimum pretreatment for this MD process.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.4
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• pp.214-223
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• 2003

A reliability analysis is straightforwardly applied to the sloped coastal structures against the random wave overtopping. A reliability function can be directly derived from a empirical formula in which may take into account many variables associated with the random wave overtopping. The probability of failure exceeded the allowable overtopping discharge can be evaluated as a function of dimensionless crest height with some reasonable statistical properties and distribution functions of each random variable. Some differences of probabilities of failure occurred from variations of the slopes of structures as well as types of armour are investigated into quantitatively. Additionally, the effects of the crest width of units placed in front of the concrete cap on the probability of failure may be analyzed. Finally, the sensitivity analyses are carried out with respect to the uncertainties of random variables. It is found that the overall characteristics similar to the known experimental results are correctly represented in this reliability analyses. Also, it should be noted that the probabilities of failure may be quantitatively obtained for several structural and hydraulic conditions, which never assess in the deterministic design method. Thus, it may be possible for determination on the crest height of sloped coastal structures to consider the probability of failure of wave overtopping, by which may be increased the efficiency of practical design.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.321-328
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• 2006

In the present study extensisve numerical experiments are conducted using the CFD code, FLUENT, to investigate the energy dissipation due to perforated walls for various wall-thickness and flow conditions. A new empirical formula for energy loss coefficient considering the effect of the thickness of perforated wall is obtained based on the results of computational experiments. It is found that the energy loss coefficient decreases as the wall-thickness increases and the maximum coefficient reduction reaches upto 40% of the value calculated using the conventional formulas for the sharp-crested orifice. To check the validity of the new formula the reflection coefficient of waves due to perforated wall is evaluated and compared with the results of existing theories and hydraulic experiments. The result shows that the new formula is superior to the conventional ones.