• 콘크리트학회논문집
• /
• 제22권3호
• /
• pp.367-374
• /
• 2010

전이슬래브 시스템은 상부 전단벽 구조로부터 하부 기둥으로 하중을 전달하는 구조시스템이다. 이 시스템은 상당한 두께의 슬래브를 필요로 하므로 비경제적이며, 이 단점은 슬래브내에 중공부를 두어 해결할 수 있다. 그리고 이 시스템은 플랫플레이트 구조로써 기둥-슬래브 접합부 부근의 뚫림전단파괴을 일으키는 취성파괴의 위험이 존재한다. 따라서 중공부를 갖는 전이슬래브 시스템의 뚫림전단 성능은 매우 중요하다. 그러나 현행 기준에서는 중공부를 갖는 슬래브의 뚫림전단성능에 대한 명확한 강도산정 규정이 제시되어 있지 않다. 이 연구에서는 중공 시스템의 뚫림전단강도를 알아보기 위하여 실험적 연구를 수행하였으며, 현행기준 및 기존연구를 토대로 실험체의 전단강도를 예측하였다. 그 결과, 중공시스템의 뚫림전단강도는 기둥면으로부터 위험단면 d/2의 위치와 중공부 중심에서의 위험단면으로 계산된 값 중 작은 값으로 결정되었다. 여기서 강도 계산을 위하여 위험단면의 유효단면적을 사용하여 계산하였다.

• 설비공학논문집
• /
• 제1권2호
• /
• pp.190-201
• /
• 1989

This experimental investigation has been conducted to determine the effects of swirling angle and flow patterns on distributions of void fraction, bubble velocity and two-phase pressure drop in a vertical straight tube. Swirling angles of $0^{\circ}$ (non swirling), $30^{\circ}$, and $45^{\circ}$ were tested with air-water two components over a range of superficial air velocities. A transparent lucite tube of 38mm in internal diameter was used for the test section. The void fraction and bubble velocities were measured by means of a optical fiber probe at the upper part of the swirler in the test section. Pressure drops which seem to be closely related with flow patterns and swirling angle were measured by a differential pressure transducer. It is shown that the probability density functions of pressure drop demonstrate peculiar features for both swirling angles and flow patterns, whereas the distributions of void fraction and bubble velocities are parabolic and flat shape in the vicinity of tube center, respectively except bubbly flow in any swirling angle cases, and the void fraction increases with increasing swirling angle around the center of tube.

• 대한기계학회논문집B
• /
• 제20권1호
• /
• pp.384-398
• /
• 1996

An improved multi-channel Impedance Void Meter (IVM) is developed to measure an area-averaged void fraction. It consists of a main sensor, a reference sensor and a signal processor. The sensor was designed to be flush-mounted to the inner wall of the test section to avoid the flow disturbances. Guard electrodes are used to obtain evenly distributed electrical field in a measuring volume. A reference sensor is also installed to eliminate the drift in void signal caused by the changes in electrical properties of working fluid. The signal processor with three channels is specially designed so as to minimize the inherent error due to the phase difference between channels. As an example of applications, the mean and fluctuating components of void fraction are measured for bubbly and slug flow regime, and it is shown that IVM has good dynamic resolution which is required to investigate the structural developments of bubbly flow and the propagation of void waves in a flow channel.

• 대한설비공학회지:설비저널
• /
• 제15권3호
• /
• pp.283-291
• /
• 1986

An experimental study has been conducted to investigate characteristics of the flow patterns, its transitions and the mean local void fraction obtained from which the probe was traversed diametrically from center to wall of the test section in the vertical upward air-water flow for isothermal condition using the electrical conductivity probe. It has been shown that the probability density function of the mean local void fraction measured statistically from a Fast Fourier Transform becomes a criterion for the flow patterns and the mean local void fraction profile is a highly function of the flow patterns.

• 대한설비공학회지:설비저널
• /
• 제16권4호
• /
• pp.383-391
• /
• 1987

An experimental investigation has been conducted to determine the flow pattern for two-component , two-phase mixtures which flow vertically upwards in concentric annuli based on the measurement for the local void fraction and the distribution of the local void fraction in various radial locations in the annular gap. The annular test section consists of a lucite outer tube whose inside diameter is 38mm and a stainless steel rod, The rod diameter is either :2mm,16mm or 20mm. It is demonstrated that the probability density function of the fluctuations in void fraction may be used as an flow pattern indicator and the local void fraction distribution depends on the flow pattern and radial location in the annular passage.

• 한국도로학회논문집
• /
• 제18권2호
• /
• pp.37-42
• /
• 2016

PURPOSES : The objective of this study is to determine the optimal frequency of ground penetrating radar (GPR) testing for detecting the voids under the pavement. METHODS : In order to determine the optimal frequency of GPR testing for void detection, a full-scale test section was constructed to simulate the actual size of voids under the pavement. Voids of various sizes were created by inserting styrofoam at varying depths under the pavement. Subsequently, 250-, 500-, and 800-MHz ground-coupled GPR testing was conducted in the test section and the resulting GPR signals were recorded. The change in the amplitude of these signals was evaluated by varying the GPR frequency, void size, and void depth. The optimum frequency was determined from the amplitude of the signals. RESULTS: The capacity of GPR to detect voids under the pavement was evaluated by using three different ground-coupled GPR frequencies. In the case of the B-scan GPR data, a parabolic shape occurred in the vicinity of the voids. The maximum GPR amplitude in the A-scan data was used to quantitatively determine the void-detection capacity. CONCLUSIONS: The 250-MHz GPR testing enabled the detection of 10 out of 12 simulated voids, whereas the 500-MHz testing allowed the detection of only five. Furthermore, the amplitude of GPR detection associated with 250-MHz testing is significantly higher than that of 500-MHz testing. This indicates that 250-MHz GPR testing is well-suited for the detection of voids located at depths ranging from 0.5~2.0 m. Testing at frequencies lower than 250 MHz is recommended for void detection at depths greater than 2 m.

• 한국농공학회논문집
• /
• 제57권1호
• /
• pp.11-23
• /
• 2015

In this study the laboratory test for hydraulic conductivity and the seepage analysis with finite element method on measurement section of sea dike embankment were performed for the purpose of estimating the relative density of embankment from the measured pore water pressures, and both results of the test and the analysis were coupled with the method of estimating seepage blocking state with the hydraulic head loss rate in sea dike embankment. The relationship of void ratio vs hydraulic head loss rate was obtained by setting hydraulic conductivity as common ordinate on the relationships between the void ratio and the hydraulic conductivity and between the hydraulic conductivity and the hydraulic head loss rate. The void ratio on the segment between measuring points was calculated from the coupled relationship of the void ratio vs the hydraulic conductivity. The allowable upper and lower limits of hydraulic head loss rate and those of void ratio on the safety were generated from the coupled relationship between the laboratory compaction test and the sedimentation test. Current hydraulic head loss rate and void ratio were evaluated in the allowable range between upper and lower limits.

• 한국강구조학회 논문집
• /
• 제24권3호
• /
• pp.313-323
• /
• 2012

본 연구의 목적은 콘크리트량을 저감시키기 위해 오메가형 강판을 삽입한 철선일체형 중공 데크플레이트 슬래브와 용접 H형강합성보의 휨성능 및 $CO_2$ 감소량을 평가하는 것이다. 중공 데크플레이트 슬래브는 콘크리트의 양을 줄여 건물의 중량을 저감시킬 수 있을 뿐만 아니라 환경친화적인 구조물을 확보할 수 있다. 따라서 본 연구에서는 액츄에이터를 이용한 단조가력 실험을 실시하여 합성보의 휨성능을 평가하였으며, 기존연구를 바탕으로 이산화탄소의 배출량을 정량적으로 평가하였다. 주요 실험 변수는 오메가형 강판 상부 슬래브의 콘크리트 두께, 오메가형 강판의 단속길이 등이다. 실험결과, 용접 H형강 보에 오메가형 강판을 삽입한 철선일체형 중공 데크플레이트 슬래브를 적용하여 합성보로 사용하면, 콘크리트 양의 감소에 의한 합성보의 휨내력 저하는 없는 것으로 나타났으며, $CO_2$ 절감에도 효과적인 것으로 나타났다.

• Nuclear Engineering and Technology
• /
• 제10권2호
• /
• pp.79-86
• /
• 1978

본 연구의 목적은 수직 연료봉 집합체에서 물-공기 2상 유동일 경우 공기분포현상에 관한 실험적 데이타를 얻는데 있다. test-section은 6각형, 61개의 연료봉 집합체로 구성되며, 각 연료봉은 helical spacers로 감겨져 있고, 사용되는 유체는 공기와 물이다. 실험은 크게 2부분으로 나누어서 물의 유량을 일정하게 하고 공기의 유량을 증가시킬 경우와 물자 공기의 유량을 동시에 증가시킬 경우의 공기분포현상에 관해 실시하였다. 공기는 4구멍을 통해 각각 주입시켰다. 보이드율의 측정은 전기적 Void-needle 방법을 적용하였으며 그 결과는 도표를 통해 보여주고 있다. 이 실험의 결과로써 물의 유랑을 증가시킬 수록 공기분포는 균일하게 되며, 공기 공급 위치는 공기분포에 큰 영향을 미치고 있음이 입증되었다.

• Progress in Superconductivity
• /
• 제3권2호
• /
• pp.218-223
• /
• 2002

The void volume fraction of cables is one of the effective parameters to characterize the joints of superconducting magnet. Because electrical resistance and cooling stability in the CICC (Cable-in-Conduit Conductors) joint are governed by the void volume fraction, it should be controlled constantly in the termination of cable. The change of cross-section shape in the cable was fecund during the unidirectional compaction of terminal sleeve. The non-uniform thickness of the sleeve after compaction is expected because the loading is not taxi-symmetric, and the plastic flow is also not axi-symmetric. The CICC was compacted from 45% void volume fraction to 15% by using two-piece compaction jig, which could be pressed mini-directionally. Commercial code, ABAQUS, was used to analyze the plastic flow in the sleeve during the unidirectional compaction. The increment of radius of curvature of compaction jig could minimize the change of the deformed shape of cables. The calculated results were agreed with the experimental observations.