• Journal of Energy Engineering
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• v.17 no.2
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• pp.116-123
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• 2008

In order to study the heat transfer, effectiveness and pressure drop of an internal heat exchanger (IHX) for $CO_2$, heat pump under heating condition, the experiment and numerical analysis were performed. Four kinds of IHXs were used. The section-by-section method and Hardy-Cross method were used for the numerical analysis. The effects of IHX on the flow rate of refrigerant, the IHX length, the operating condition of a gas-cooler and an evaporator and the type of IHXs were investigated. With increasing the flow rate, the heat transfer rate increased about 25%. The heat transfer of the micro-channel tube was larger about 100% than that of the coaxial tube. With increasing the IHX length, the heat transfer rate decreased. The low-side pressure drop was larger compared with that of the high-side. And the pressure drop of the microchannel tube was larger about 100% than that of the coaxial tube. With increasing the high-side temperature and decreasing the low-side temperature, the heat transfer rate increased about 3%. From this study, we can see that new correlation on $CO_2$ heat transfer characteristics and tube type is necessary.

• Journal of Korean Society of Disaster and Security
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• v.11 no.1
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• pp.31-38
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• 2018

The 99.1% of small dam and most of the levees in Korea are soil dam which can be constructed with lower cost and less effort compared with ones made of concrete. However, they are so vulnerable to overflow. Sudden collapses of these strucrues lead to increase flow rate rapidly, which may cause catastrophic problems in downstream regions. In this study, the experimental study on the collapse delay effect of riprap that was laid on slope of soil levee was carried out. A prismatic rectangular open channel was used and three different sizes of the riprap were installed on slope of a scaled earth dam. A new formula for the collapse time of the levee with the installation of riprap was presented, using the previous researches and the dimensional analysis. In this process, an unsteady flow condition was considered to derive the deviation time of the riprap. And additional experiments were conducted to understand the effect of reinforcement of riprap, and it was found that the reinforcement of riprap was more effective than twice sizing of intial riprap. If the collapse time is delayed, EAP (Emergency Action Plan) and forecasting can greatly reduce the degree of flood damage. Also, it will be meaningful that the results of this study are used for river design.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.378-385
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• 2017

This study investigated the design of a snap fit, which is widely used for fastening plastic parts. We analyzed the assembly mechanism of a lock snapfit, measured the assembly force and separation force based on the design of experiments, and derived a regression equation through an analysis of variance. The response surface methodology was also used. Polybutylene terephthalate was used to fabricate specimens, and the assembly force and separation force were measured using a micro-tensile tester. The length, width, thickness, and interference were considered as factors. A second-order regression model was used to derive the regression equation. The assembly force decreased with increasing length and width, but it increased with increasing thickness and interference. The finite element method was used to analyze the assembly mechanics. The width decreased the assembly force by increasing the ductility. The influences of the factors for low assembly force and high release force were shown to be opposite to each other. It was necessary to design a structure that minimized the assembly force while maintaining an appropriate level of separation force.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.11
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• pp.2689-2696
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• 2015

Radioactive isotopes which are manufactured using a cyclotron in a radioisotope used for radiation diagnosis is affected by the production yield according to size and shape of the beam and beam uniform degree from irradiated location when the proton beam investigated the target by cyclotron. Therefore, in this paper developed the BPM(Beam Profile Monitor) device capable of measuring the beam cross-section at the cyclotron beam line. It was configured so as to be able to remote control the BPM device in LabView and used the BPM program it was to be able to easily monitor and display to analyze the graph of two-dimensional graph and a three-dimensional beam distribution numerical information of the beam obtained while scanning the tungsten wire to the X and Y axis. The time it takes to measure the beam can be confirmed 37seconds when step motor driving speed was 2000pps. Through a beam readjusted based on the measured beam distribution information by optimizing the beam distribution it can be made to maximize the RI production yield and contribute supply stabilization.

• The Korean Journal of Petroleum Geology
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• v.10 no.1_2 s.11
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• pp.18-22
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• 2004

To identify and interpret the distribution and the characteristics of the gas hydrate layers in the Ulleung Basin, we have surveyed and gathered the multi-channel seismic data, Chirp sub-bottom profiler, SeaBeam and 12 m piston core samples since 1996. In previous works, high-resolution seismic profiles showed acoustic anomalies such as acoustic void, acoustic turbidity and pock mark which indicate the presence of gas-charged sediments. The patterns of horizontal degassing cracks originated from free methane expansion is the strong indicator of shallow gas-charged sediments in the core samples. The observation of submarine slides and slumps from destabilizing the sediments in the southern part of the Ulleung Basin may also point out that the gas had been released from gas hydrate dissociation during lowstand of sea level. The multi-channel seismic data show BSR, blanking and phase reversal. The gas hydrate layers above which large-scale shallow gases are distributed exist at the depth of about 200 m from the sea-floor with water depth of 2,100 m. From the interpretation of seismic sections in the southern Ulleung Basin, gas hydrate layers occur in the Pleistocene-Holocene sediments. These gas-charged sediments, acoustic anomalies and BSR may be all related to the existence of gas hydrate layers in the study area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.195-202
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• 2004

The shell due to the effect of initial normal pressures on the shell surface was based on the assumption that the directions of the pressures are always normal to the undeformed shell surface, and that the change in the surface area of the shell is negligible. But the fact that the pressure are always normal to the deforming surface leads "follower force". The follower effect in the analysis can significantly alter the solution for natural frequency and buckling load as compared to the case when the direction of the pressures are assumed to be normal to the uniform shell surface. The expression for the part of strain energy contribution from normal pressure due to the effect of follower force was derived and added to the element stiffness matrix of axisymmetric shell. In the case of increasing external pressure, the natural frequencies decrease until one of them reaches zero. Theoretically the smallest applied load that reduces the frequency of any mode to zero, will have same magnitude as that of the buckling load. In order to determine the bucking load of the shell a few sets of frequencies are computed and the results considering the follower effects are well with the exact solution while the case without that are quite different. But in case of hemispherical dome, there are little difference in buckling pressure between with and without the effect of follower force.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.17 no.4
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• pp.418-425
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• 1988

Since conventional computer program is workable only with velocity boundary condition, in practical fluid passage such as clean room which usually have wide inlets and outlets, it is not easy to measure velocity itself because of its vector property. Furthermore a certain assumption of velocity at boundaries may lead to physically unreasonable results. From this motivation, we have developed a computer program to predict whole flow field imposed on pressure-based boundary condition which can be measured by relatively simple method. The only additional velocity boundary condition that should be imposed on to make the problem unique, are no slip condition at all walls and zero cross stream velocity at inlet. The result of present study was compared with that by Bernoulli equation being used practically. They were coincident well each other within 5%, therefore the validity of the present method is proved. In the present work, the flow field in a clean room subject to pressure-based boundary conditions at an inlet and two exits was predicted numerically. The pressure difference between the inlet and the left exit which keeps relatively low pressure among two exits is fixed as 150[Pa] and the pressure at the right exit is varied from zero to 150[Pa] by the increment of 25[Pa]. For each cases the flow characteristics in the clean room, the velocity profile at the inlet, and the flow rate through the two exits was predicted. The flow rate through the right exit imposed on relatively higher pressure than the left exit decreased linearly according to the increase of pressure of the right exit. When the pressure of the right exit is increased enough to cause back flow at the exit, the flow rate is rapidly decreased.

• Journal of Conservation Science
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• v.37 no.5
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• pp.505-515
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• 2021

In this study, we evaluated the slope stability of the Pohang Daljeon-ri columnar joint (Natural Monuments # 415) and calculated the maximum energy, jumping height and moving distance of rockfalls using a simulation. Based on the results, we established the range of rockfall risk. The slopes of the Pohang Daljeon-ri columnar joint have dip directions of 93.79°, 131.99°, 165.54° and 259.84° from left (SW) to right (NE). Furthermore, they have a fan-like shape. The Pohang Daljeon-ri columnar joints are divided into four sections depending on the dip direction. The measurement results of the discontinuous face show that zone 1 is 125, zone 2 is 261, zone 3 is 262, zone 4 is 43. The results of slope stability analyses for each section using a stereographic projection method correspond to the range of planar and toppling failure. Although it is difficult to diagnose the type of failure, risk evaluation of currently falling rocks requires further focus. The maximum movement distance of a rockfall in the simulation was approximately 66 m and the rockfall risk range was the entire area under slope. In addition, it is difficult to forecast where a rock will fall as it rolls in various directions due to topographic factors. Thus, the installation of measures to prevent falling is suggested to secure the stability based on the results of the rockfall simulations and its probabilistic analysis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.32-39
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• 2021

Recently, necessities of steel form for reinforced concrete beam and girder have been emphasized in building structures for the reduction of the construction period and the labor cost. SY Beam was developed for the these purposes and is roll-formed using thin steel plate. On this research, we tried to evaluate and verify the performance and behavior of SY Beam under construction loading stage as like pouring in situ concrete. For the standard shape of SY beam, structural modelling with various steel thicknesses has carried out using MIDAS GEN program. From results of modelling, the width and height of SY Beam were determined 600mm and 400mm respectively. For 3 SY Beams, the loading experiment was performed to measure vertical and horizontal displacement under stacking sand, concrete block, and bundle of rebar. As a result, the vertical deflection showed a tendency to decrease as the thickness increased. In the horizontal displacement, the trend according to the thickness was not clearly observed. From the evaluation on the loading experiment, it is considered that the SY Beam can secure both workability and structural safety. In particular, the SY Beam(1.2mm) hardly generates horizontal displacement, so it has excellent load-bearing capacity. So, we judged that the SY Beam with 1.2mm steel plate has excellent performance and consider to be immediately commercially available.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.149-156
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• 2021

FRP has been proposed to replace the steel as a reinforcement in the concrete structures for addressing the corrosion issue. However, FRP-Rebar does not behave in the same manner as steel because the properties of FRP are different. For example, FRP-Rebar has a high tensile strength, low stiffness, and linear elastic behavior which results in a difference bonding mechanism to transfer the load between the reinforcement and the surrounding concrete. Therefore, bonding behavior between FRP-Rebar and concrete has to be investigated using the bonding test. So, Pull-out test has been used to estimate bond behavior because it is simple. However, the results of pull-out test have a difference with flexural-boding behavior of FRP-Rebar concrete member. So, it is needed to evaluate the real fleuxral-bonding behavior. In this study, the evaluation method to flexural-bonding behavior of FRP-Rebar concrete member was reviewed and compared. It was found that the most accurate evaluation method for the fleuxral-bonding behavior of FRP-Rebar concrete member was splice beam test, however, the size and length of specimen have to increase than other test method and the design and analysis of splice beam is complex. Meanwhile, characteristics of concrete could be reflected by using arched beam test, unlike hinged beam test which is based on the ignored change of moment arm length in equilibrium equation. However, the possibility of shear failure exists before the flexural-bonding failure occur.