• Water for future
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• v.22 no.1
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• pp.81-90
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• 1989

A numerical simulation technique of three-dimensional finite difference model is developed to study the groundwater flow system in Dejima, an upland area which faces Kasumigaura Lake. For general perspectives of the groundwater flow system, a steady state three-dimensinal model is simulated. For the sedimentary mud formations which are found in the representative formation, three situations where the horizontal permeability is equal to 10 times and 100 times of the vertical one. The finite difference grid used in the simulation has 60$\times$50$\times$30=90,000 nodes. A converged solution with a tolerance of 0.001 meter of hydraulic head is set. Having determined the flow net by using a steady state three-dimensional model, the results for the three cases of hydraulic conductivity are compared with the results of the tracer methods (Bae and Kayane, 1987). With the aid of four representative vertical cross-sections, groundwater flow systems in the study area are assumed. The results of these are reasonally good comparable with the results of the basin yield and thd recharge-discharge distribution 8.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.26 no.2
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• pp.63-81
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• 2021

In this study, we investigated the tide-induced flow patterns near the ocean outfall of the Jeju and Bomok Wastewater Treatment Plants (WTP) in Jeju Island by using measurements of Acoustic Doppler Current Meter (ADCP) and a numerical experiment with inserting passive tracer into a regional ocean model. In late spring of 2018, the ADCP measurements showed that tidal currents dominate the flow patterns as compared to the non-tidal components in the outfall regions. According to harmonic analysis, the dominant type of tides is mixed of diurnal and semi-diurnal but predominantly semidiurnal, showing stronger oscillations in the Jeju WTP than those in the Bomok WTP. The tidal currents oscillate parallel to the isobath in both regions, but the rotating direction is different each other: an anti-clockwise direction in the Jeju WTP and a clockwise in the Bomok WTP. Of particular interest is the finding that the residual current mainly flows toward the coastline across the isobath, especially at the outfall of the Bomok WTP. Our model successfully captures the features of tidal currents observed near the outfall in both regions and indicates possibly high persistent pollutant accumulation along the coasts of Bomok.

• Journal of Korea Water Resources Association
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• v.54 no.7
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• pp.495-507
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• 2021

With the recent industrial development, accidental pollution in riverine environments has frequently occurred. It is thus necessary to simulate pollutant transport and dispersion using water quality models for predicting pollutant residence times. In this study, we conducted a field experiment in a meandering reach of the Sum River, South Korea, to validate the field applicability and prediction accuracy of RAMS+ (River Analysis and Modeling System+), which is a two-dimensional (2D) stream flow/water quality analysis program. As a result of the simulation, the flow analysis model HDM-2Di and the water quality analysis model CTM-2D-TX accurately simulated the 2D flow characteristics, and transport and mixing behaviors of the pollutant tracer, respectively. In particular, CTM-2D-TX adequately reproduced the elongation of the pollutant cloud, caused by the storage effect associated with local low-velocity zones. Furthermore, the transport model effectively simulated the secondary flow-driven lateral mixing at the meander bend via 2D dispersion coefficients. We calculated the residence time for the critical concentration, and it was elucidated that the calculated residence times are spatially heterogeneous, even in the channel-width direction. The findings of this study suggest that the 2D water quality model could be the accidental pollution analysis tool more efficient and accurate than one-dimensional models, which cannot produce the 2D information such as the 2D residence time distribution.

• Journal of Biomedical Engineering Research
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• v.20 no.1
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• pp.29-36
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• 1999

The objective of this study is to analyse the flow field in the branching duct by visualizing the flow phenomena using the PIV system. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. Water was used as the working fluid and the conifer powder as the tracer particles. The single-frame and two-frame methods of the PIV system and 2-frame of the grey level correlation method are applied to obtain the velocity vectors from the images captured in the flow filed. The velocity distributions in a lid-driven cavity flow are compared with the so-called standard experimental data, which was obtained from by 4-frame method in order to validate experimental results of the PIV measurements. The flow patterns of a Newtonian fluid in a branching duct were successfully visualized by using the PIV system and the sub-pixel and the area interpolation method were used to obtain the final velocity vectors. The velocity vectors obtained from the PIV system are in good agreement with the numerical results of the 3-dimensional branch flow. The results of numerical analyses and the PIV experiments for the three-dimensional flows in the branch ing duct show the recirculation zone distal to the branching point and the sizes of the recirculation length and height of the tow different methods are in good agreement.

• The Korean Journal of Nuclear Medicine
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• v.37 no.5
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• pp.288-300
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• 2003

Purpose: To obtain regional blood flow and tissue-blood partition coefficient with time-activity curves from ${H_2}^{15}O$ PET, fitting of some parameters in the Kety model is conventionally accomplished by nonlinear least squares (NLS) analysis. However, NLS requires considerable compuation time then is impractical for pixel-by-pixel analysis to generate parametric images of these parameters. In this study, we investigated several fast parameter estimation methods for the parametric image generation and compared their statistical reliability and computational efficiency. Materials and Methods: These methods included linear least squres (LLS), linear weighted least squares (LWLS), linear generalized least squares (GLS), linear generalized weighted least squares (GWLS), weighted Integration (WI), and model-based clustering method (CAKS). ${H_2}^{15}O$ dynamic brain PET with Poisson noise component was simulated using numerical Zubal brain phantom. Error and bias in the estimation of rCBF and partition coefficient, and computation time in various noise environments was estimated and compared. In audition, parametric images from ${H_2}^{15}O$ dynamic brain PET data peformed on 16 healthy volunteers under various physiological conditions was compared to examine the utility of these methods for real human data. Results: These fast algorithms produced parametric images with similar image qualify and statistical reliability. When CAKS and LLS methods were used combinedly, computation time was significantly reduced and less than 30 seconds for $128{\times}128{\times}46$ images on Pentium III processor. Conclusion: Parametric images of rCBF and partition coefficient with good statistical properties can be generated with short computation time which is acceptable in clinical situation.