Dong-Gu Kim

Origins of the impedance change in impedance cardiography by a three-dimensional finite element model

A three-dimensional finite-element model of the thorax and neck using eight-node trilinear hexahedron elements was constructed to investigate the impedance change associated with various physiological events during systole. A three-dimensional finite-element code was developed to solve the generalized Laplace equation with Dirichlet and homogeneous Neumann boundary conditions. The current in each element as well as potential at each node was calculated. The results suggest that an approximately linear relationship exists between the impedance change and blood volume change in the aorta. This is a promising result since the relationship helps explain the correlation between impedance cardiography and invasive techniques. Impedance changes due to blood volume changes in the aorta and ventricles, the lung-resistivity change, and the blood-resistivity change were calculated for standard impedance electrode configurations.<<ETX>>

Inter-comparison of accuracy of discharge measurement methods - a case study performed in the Dalcheon River downstream of the Goesan Dam.

본 연구에서는 괴산댐 하류 달천에서 6가지 직접 유량 측정 방법-유속면적법, 봉부자법, ADCP이동측정법, ADCP정지 측정법, 전자파표면유속계, LSPIV-을 적용하고, 이를 댐 방류량 및 유속면적법과 비교함으로써 정확도를 상호 평가하였다. 이를 위해 2005년부터 2010년까지 실시된 총 39회의 유량측정결과가 분석되었다. 댐 방류량과의 비교 결과, 봉부자법을 제외한 나머지5가지 방법은 평균 6.2% 이내의 절대값오차를 나타냈다. 유속면적법과 다른 4가지방법을 비교할 경우, 전자파표면유속계는 7.35%, 나머지 3가지 방법은 6% 이내의 절대값오차를 나타냈다. 봉부자법은 댐 방류량 및 유속면적법과 비교하여도 오차의 범위가 크게 나타났는데, 이에 대해서는 추가적인 검증이 필요하다. 【Relative accuracy of six discharge measurement methods-velocity-area method, rod-float method, ADCP moving-vessel method, ADCP fixed-vessel method, electromagnetic wave surface velocimeter (EWSV), LSPIV- is evaluated by comparing discharges measured by them with dam released discharges. Data from 39 times of concurrent discharge measurement campaigns are analyzed. Except the rod-float method, measured discharges show absolute errors less than 6.2% with dam discharges. When the four methods is evaluated by being compared with discharges measured with the conventional velocity-area method, discharges with electromagnetic wave surface velocimetry shows 7.35% of absolute errors and other three methods shows absolute errors less than 6%. The rod-float method, which shows large discrepancy compared with dam and velocity-area method, need complementary verification.】

Short-term Change in Channel Morphology of the Naeseong Stream before the Operation of Yeongju Dam, Korea

내성천은 산지를 사행하는 모래하천으로 오랫동안 그 하천지형학적 특성을 유지해왔다. 그러나 최근 식생의 활착으로 종래의 경관을 상실해 가고 있다. 본 연구에서는 내성천 장기조사 연구의 일환으로 내성천의 56.8 km 구간을 대상으로 지난 2012 - 2016년 기간에 발생한 지형변화를 분석하였다. 항공 라이다 및 하천측량...

Analysis on Spatial Variability of Rainfall in a Small Area

This study deployed six rain gauges in a small area for a dense network observing rainfall and analyzed the spatial variability of rainfall. They were arranged in a rectangular grid with equal space of 60 m. The rainfall measurements from five gauges were analyzed during the period of 50 days because one was seriously affected by alien substance. The maximum difference in cumulative rainfall from them is approximately 38.5 mm. The correlation coefficients from hourly rainfall time series differ from each other while daily rainfall coincide. The coefficient of variation in hourly rainfall varies up to 224% and that in daily rainfall up to 91%. The results from uncertainty analysis show that with only four rain gauges areal mean rainfall cannot be estimated over 95% accuracy. For reliable flood prediction and effective water management it is required to develop a new technique for the estimation of areal rainfall.

A Water Surface Detection Method by Correlation Analysis of Watermark Images with Time Interval

The aim of this study is to suggest a detection method of water surface location and its evaluation results of application for same vertical position in two successive images with time interval including both staff gauge and water surface. A specific rectangular inspection area is defined from the top of watermark and then the correlation coefficients for the inspection area of the same position of two images with short time interval is calculated. Accordingly, it is possible to identify differences between changing area and fixed area of pixel density by the water flow. The photographs taken in the laboratory were analyzed in order to validate the proposed technique. As the result of the experiment, it is identified that characteristic of correlation coefficients depends on the size of the inspection area. In the case that the inspection area is within the entire width of the watermark, water surface characteristic according to correlation coefficients is clearly noticeable. Thus, it is identified that the proposed technique can be utilized to search water surfaces. Besides, using corelation analysis of two images with time interval, it is identified that error range between 10 and 42cm was reduced in the level of 2.6cm or less in the contaminated photo of existing image stage gauge. Therefore, it is expected that the suggested method can be utilized to enhance image stage gauge performance improving the previous water surface detection method.

Development of an Acoustic Velocity Profiler by Using Pulse Repetition Frequency Technique

An acoustic velocity profiler is developed, which is able to be used for open-channel flow measurement. It measures flow velocity based Doppler effect on acoustic signals, which is estimated by using pulse repetition frequency technique. Laboratory and field tests were made to verify velocity measuring performance of the developed device. It is confirmed that the acoustic velocity profiler can normally measure vertical velocity profile in the range above 0.1 m from the bottom and has equivalent performance to commercial acoustic velocity measuring devices.