• Journal of Wetlands Research
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• v.12 no.3
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• pp.57-65
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• 2010

This study was conducted to present primary data on the change of the physical characteristics of reservoir sediments for understanding the sedimentation. The records of the annual summation of the precipitation of >50mm per day (AP50) were compared with changes of bulk density, organic matter, mean grain-size, and sand ratio in sediment cores sampled from three reservoirs without dredging record. Reservoir sediments, characterized by mineral soil, contained organic matters originated from the debris of terrestrial plants, and changes of organic matter were related to changes of grain-size flowing into reservoirs when sediments of fine sandy loam showed 10% of organic matter contents. Rapid changes of grain-size and sand ratio in the sediment cores were associated with the increase and decrease of precipitation, and fluctuation of water level and water flow in reservoirs might have influenced on the formation of sediments in reservoirs. Records of AP50 suggested that sediments could accumulate more than about 30 within the short period of 10 years. The accumulated sediments in a short time can reflect the effect of natural and anthropogenic events on the physical characteristics of sediments.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.46-53
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• 2016

It is required to predict a limit cycle amplitude controlled by system's nonlinear behavior as well as an eigen-frequency and initial growth rate of instabilities under the linear motions, in order to fully understand combustion instabilities in a lean premixed gas turbine combustor. Special focus of the current work is placed on the limit cycle amplitude prediction using flame describing function(FDF) where the ratio of a heat release fluctuation to a given flow perturbation is expressed as a function of frequency and amplitude. In this study, the CFD modeling work based on RANS is carried out to obtain FDF, which makes that the nonlinear thermo-acoustic model is successfully developed for predicting the limit cycle amplitude of the combustion instability.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.2
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• pp.171-177
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• 2014

A two-dimensional particle image velocimetry (2D PIV) system in a towing tank is employed to measure a wake field of a very large crude oil carrier model with rotating propeller in self propulsion condition, to identify characteristics of wake of a propeller working behind a ship. Phase-averaged and time-averaged flow fields are measured for a horizontal plane. Scale ratio of the model ship is 1/100 and Froude number is 0.142. By phase-averaging technique, trajectories of tip vortex and hub vortex are identified and characteristic secondary vortex distribution is observed in the hub vortex region. Propeller wake on the starboard side is more accelerated than that on the port side, due to the difference of inflow of propeller blades. The hub vortex trajectory tends to face the port side. With the fluctuation part of the phase-averaged velocity field, turbulent kinetic energy (TKE) is also derived. In the center of tip vortex and hub vortex region, high TKE concentration is observed. In addition, a time-averaged vector field is also measured and compared with phase-averaged vector field.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.432-437
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• 2010

A new device injecting secondary fuel behind flameholder was invented and tested in order to reduce low frequency combustion instability of combustor using V-gutter flameholder. Specially designed combustion device could make large combustion instability up to 180 dB successfully, and newly invented device made a success to reduce 110~120Hz low frequency pressure pulsation up to 84%. It was found that the fuel flow rate of secondary fuel supplying behind flameholder was the only parameter which dominates reduction of instability. It is considered that stabilized flame with sufficient secondary fuel can lead to break the connection between combustion system and acoustic system due to independence of flame from fluctuation of main fuel resulted from synchronization with acoustic wave.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.315-323
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• 2010

This work investigates the influence of water compressibility on pressure pulsations induced by rotor-stator interaction (RSI) in hydraulic machinery, using the commercial CFD solver ANSYS-CFX. A pipe flow example with harmonic velocity excitation at the inlet plane is simulated using different grid densities and time step sizes. Results are compared with a validated code for hydraulic networks (SIMSEN). Subsequently, the solution procedure is applied to a simplified 2.5-dimensional pump-turbine configuration in prototype with different speeds of sound as well as in model scale with an adapted speed of sound. Pressure fluctuations are compared with numerical and experimental data based on prototype scale. The good agreement indicates that the scaling of acoustic effects with an adapted speed of sound works well. With respect to pressure fluctuation amplitudes along the centerline of runner channels, incompressible solutions exhibit a linear decrease while compressible solutions exhibit sinusoidal distributions with maximum values at half the channel length, coinciding with analytical solutions of one-dimensional acoustics. Furthermore, in compressible simulation the amplification of pressure fluctuations is observed from the inlet of stay vane channels to the spiral case wall. Finally, the procedure is applied to a three-dimensional pump configuration in model scale with adapted speed of sound. Normalized Pressure fluctuations are compared with results from prototype measurements. Compared to incompressible computations, compressible simulations provide similar pressure fluctuations in vaneless space, but pressure fluctuations in spiral case and penstock may be much higher.

• Journal of Soil and Groundwater Environment
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• v.9 no.3
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• pp.27-32
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• 2004

The oceanic tides have an effect on groundwater levels in coastal fractured rock aquifers. The observed groundwater table fluctuations caused by the effective stress through an aquifer are shown as sine curves similar with tidal fluctuation. To estimate a hydrogeologic parameter, tidal method is utilized with groundwater level fluctuations of two monitoring wells. Cross correlation function is used to calculate time lags between observed groundwater levels and tide, and the deeper well shows longer time lag. The storage coefficients calculated by using tidal efficiency and time lag show large differences. The storage coefficients obtained by using time lags are close to the result of slug test, and that of the deeper well shows closer value by slug test. The tidal efficiency is unsatisfied to apply in the tidal method because of an effect of phreatic aquifer and the vertical flow of groundwater through fractured confining bed. This tidal method can be an economical and effective way to define the parameter by considering the location of observation well and hydrogeologic characteristics of a coastal aquifer.

• Journal of Korean Medicine for Obesity Research
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• v.3 no.1
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• pp.75-84
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• 2003

Objective : In Western medicine, the cause of obesity include overeating, lack of exercise, genetic factor, endocrinal impediment and psychological factor. Since the society becomes more complexed and the tensions among social members gets intensified, psychological factor getting more important. In Oriental medicine, Seven Emotion(七情, in oriental medical term) as an emotional stressor was thought to be a factor of obesity. Therefore the purpose of this study is to examine the relationship between Seven Emotion and obesity in detail. Methods : overview the stress with the view of Oriental medicine and research the relationship between Seven Emotion as an emotional stressor and obesity. Results : 1. Seven Emotion can be understood as an emotional stress in Western medicine. If Seven Emotion is excessive, its extreme mental stimulation causes physical illness. 2. Having influence upon the function of internal organs, excessive Seven Emotion causes obesity. Since it hinders normal flow of Gangi(肝氣), Seven Emotion disturbs healthy function of Bi-Wi(脾胃) and normal fluctuation of Qi. Consequently, obesity is resulted from the accumulation of fat since normal metabolism of body is disrupted. 3. In Seven Emotion-Anger(怒), Joy(喜), Anxiety(憂), Thought(思), Sorrow(悲), Fear(恐), Surprise(驚)-give rise to Gan-bi-bul-wha(肝脾不和), Sim-hi-yang-huh(心脾兩虛), Bi-qi-huh(碑氣虛), Dam-sup-jeo-po(痰濕沮胞) and Wi-wha-sang-youm(胃火上炎) in type of symptom in obesity and therefore, cause obesity.

• Journal of Soil and Groundwater Environment
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• v.26 no.6
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• pp.1-17
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• 2021

Self-potential (SP) surveys measure naturally occurring differences in electrical potential in the absence of artificial sources and have been applied to various fields since the first application in mineral explorations. Among various causes of SP occurrences, streaming potential is generated by the flow of groundwater, and makes SP surveys suitable for the exploration of groundwater table fluctuation, fractures, sinkholes and landslide occurrences. Recently, there has been many studies that applied SP surveys to monitor water leakage through dikes and embankments. In this review paper, we first review the characteristics and theoretical backgrounds of streaming potential in saturated or unsaturated porous media to introduce it in the embankment among various application field. After the review of the background theory, we review the past cases of field SP surveys on dikes and embankments and also the characteristics of field streaming potential data in the surveys. Further, by analyzing past studies of qualitative as well as quantitative interpretation of SP survey data, we show the possibility of quantitative interpretation of streaming potential data obtained on dikes and embankments. Consequently, it is hope that this review paper helps researches on SP surveys on dikes and embankments, and provides basis for interpretation methods of the SP data to identify leaked area and further leakage rate (or permeability).

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.71-84
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• 2020

In order to improve the performance of marine centrifugal pump, a centrifugal pump whose specific speed is 66.7 was selected for the research. Outlet diameter D2, outlet width b2, blade outlet angle β2, blade wrap φ and blade number z of the impeller were chosen as the variables. The maximum weighted average efficiency and the minimum vibration intensity at the base were calculated as objectives. Based on the Latin Hypercube method, the impeller was numerically optimized. The numerical results show that after optimization, the amplitudes of pressure fluctuation on the main frequency at different monitoring points decrease in varying degrees. The radial force on impeller decreases obviously under off-design flow rates and is more symmetrical during the operation of the pump. The variation of the axial force is relatively small, which has no obvious relationship with the rotating angle of the impeller. The energy performance and vibration experiment was performed for verifying. The test results show that the weighted average efficiency under 0.8Qd, 1.0Qd and 1.2Qd increases by 4.3% after optimization. The maximal vibration intensity at M1-M4 on the pump base reduced from 0.36 mm/s to 0.25 mm/s, decreasing by 30.5%. In addition, the vibration velocities of bracket in pump side and outlet flange also have significant reductions.

• Atmosphere
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• v.33 no.4
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• pp.343-354
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• 2023

Turbulence produced on roadways is one of the major factors determining the dilution rates at the initial stage of traffic emissions of air pollutants and, thus, the distribution of air pollutants near the roadways. Field experiments were conducted on Gyeongbu Highway, one of the busiest highways in Korea, for 4~7 days in winter, spring, and summer. Two three-dimensional ultrasonic anemometers were installed on both sides of the highway to estimate turbulence intensities (vertical wind fluctuation and kinetic turbulence energy) induced by the roadway. Roadway-induced turbulence consists of three components: structural road-induced turbulence (S-RIT), thermal road-induced turbulence (T-RIT), and vehicle-induced turbulence (VIT). The contribution of T-RIT to the total RIT was insignificant (less than 10%), and the majority of RIT was S-RIT (by the highway embankment) and VIT. In this study, we propose the empirical relationships of VIT as a function of traffic density and wind speed under free-flow traffic conditions. Although this empirical relationship appears to underestimate the VIT, it can be applied to the air quality models easily because the relationship is simple and only needs readily obtainable input variables (wind speed and traffic information).