• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.2
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• pp.153-170
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• 2022

Waterjet has been comprehensively used in urban areas owing to a suitable technique for cutting concrete and rock, and low noise and vibration. Recently, the abrasive waterjet technique has been adopted and applied by the Korea Atomic Energy Research Institute to demolish concrete plugging without disturbing and damaging In-situ Demonstration of Engineered Barrier System in the disposal research tunnel. In this study, the use of abrasive waterjet in the tunnel was evaluated for practical applicability and the existing cutting model was compared with the experimental results. As a variable for waterjet cutting, multi-cutting, water flow rate, abrasive flow rate, and standoff distance were selected for the diversity of analysis. As regarding the practical application, the waterjet facilitated path selection for cutting the concrete plugging and prevented additional disturbances in the periphery. The pump's noise at idling was 64.9 dB which is satisfied with the noise regulatory standard, but it exceeded the standard at ejection to air and target concrete because the experiment was performed in the tunnel space. The experimental result showed that the error between the predicted and measured cutting volume was 12~13% for the first cut and 16% for second cut. The standoff distance had a significant influence on the cutting depth and width, and the error tended to decrease with decrement of standoff distance.

• Journal of the Korean earth science society
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• v.43 no.1
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• pp.30-40
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• 2022

Wildfires, which occur sporadically and irregularly worldwide, are distinct natural disturbances in combustible vegetation areas, important parts of the global carbon cycle, and natural disasters that cause severe public emergencies. While many previous studies have investigated the variability and changes in wildfires globally based on fire emissions, burned areas, and fire weather indices, studies on East Asia are still limited. Here, we explore the characteristics of variability and changes in wildfire danger over East Asia by analyzing the fire weather index for the 40 years-1981-2020. The first empirical orthogonal function (EOF) mode of fire weather index variability represents an increasing trend in wildfire danger over most parts of East Asia over the last 40 years, accounting for 29% of the total variance. The major contributor is an increase in the surface temperature in East Asia associated with global warming and multidecadal ocean variations. The effect of temperature was slightly offset by the increase in soil moisture. The second EOF mode exhibits considerable interannual variability associated with the El Nino-Southern Oscillation, accounting for 17% of the total variance. The increase (decrease) in precipitation in East Asia during El Nino (La Nina) increases (decreases) soil moisture, which in turn reduces (increases) wildfire danger. This dominant soil moisture effect was slightly offset by the temperature increase (decrease) during El Nino (La Nina). Improving the understanding of variability and changes in wildfire danger will have important implications for reducing social, economic, and ecological losses associated with wildfire occurrences.

• Applied Chemistry for Engineering
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• v.17 no.2
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• pp.138-143
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• 2006

Ethosome is a liquid crystalline vesicle prepared by hydration of ethanol-dissolved lecithin with a solution containing hydrophilic components. Investigation of factors affecting the entrapment efficiency and particle size of ethosomes was carried out, because the high entrapment efficiency and small particle size are prerequisite in developing ethosomes as a drug delivery system. The variations of properties of ethosomes with constituent composition and preparation method were examined using a calcein as a hydrophilic marker. It was observed that the amount of ethanol and calcein solution, phosphatidyl choline content in lecithin, preparation temperature, stirring rate, and PBS addition method had a considerable effect on the properties of ethosome. Sonication treatment resulted in the reduction of entrapment efficiency of ethosome, which was due to the release of entrapped components in the vesicles by strong sonication vibration.

• Explosives and Blasting
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• v.29 no.2
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• pp.67-80
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• 2011

Recently, the number of structure demolitions has increased in both civil and architecture fields due to various reasons such as redevelopment of a city, utilization of sites and restoration of deteriorated structures. In the past, domestic shell structures had been constructed with brick masonry and they were not high. Therefore, their demolition had been executed with ease. Recently, however, taller reinforced concrete shell structures have become a target for the destruction. Under these circumstances, how to efficiently demolish a structure and how to minimize effects of the destruction on environment including vibration and noise have become a main issue. One of the possible solutions is the explosive demolition. In this study, a case of explosives demolition of the stack, which is located in Jeju Thermal Power Plant in Republic of Korea and is 70 m tall, is addressed. In order to fall down the structure against the desired direction, 13.5 kg dynamite and 100 electric detonators were used.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.8
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• pp.16-21
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• 2012

The gyro sensor that made by MEMS process is generated an accumulated error(drift) and escape the zero angle following during calculation of rotate angle. This study propose BACF(Boot Angle Compensation Filter) algorithm for prevent escape zero angle and DCF algorithm for remove accumulated error. DCF algorithm is designed for acquire accurate turn of ratio by remove offset and noise components. BACF algorithm is obtained average offset that removed noise components by recursively calculate. Experimental environment, two-axis gyro sensor and mobile OIS camera mounted control board and 5Hz oscillation of ${\pm}0.5^{\circ}$ for the experiments were carried out. BACF and DCF algorithm is applied and the resulting accumulated error did not occur and exactly zero angle following results were made.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.1
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• pp.81-86
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• 2016

The valves used to control or shut off the flow through a pipeline can be divided into many different types, including gate valves, globe valves, and check valves. Globe valves, in particular, have excellent properties, and because they can easily control the flow under high-pressure conditions, they are generally used in LNG ship and steam pipelines. In this paper, a method for changing the shape of a seat was suggested to solve the valve leakage problem from a structural perspective. In addition, the stress distribution and directional deformation were compared for each model. The suggested models were thus validated, and the optimized seat structure, which includes a self-supporting capability for decreasing the amount of leakage, was determined.

• Journal of the Korea Convergence Society
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• v.5 no.2
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• pp.13-18
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• 2014

In this study, two models due to the configuration of ripper at excavator are investigated by structural and fatigue analyses. The maximum stress and deformation are happened at the axis connected with the body of working device and the direct working part respectively. Model 1 is thought to have more structural durability than model 2. Fatigue life or damage in case of 'SAE bracket history' whose load change is most severest among non-uniform fatigue loads is shown to become most unstable. But life or damage in case of 'Sample history' whose load change is slowest among non-uniform fatigue loads is shown to become most stable. These study results can be effectively utilized with the design of ripper at excavator by anticipating and investigating prevention and durability against its fatigue damage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.117-123
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• 2015

To remove heat generated during a burn-up test of nuclear fuels, the heat generation rate of nuclear fuels should be calculated accurately, and a coolant should be circulated in the test loop at an adequate flow rate. HANARO is an open pool-type reactor with an independent test loop for the burn-up test of nuclear fuels. A test rig is installed in the test loop, and a coolant is circulated through the test loop to maintain the temperature of the nuclear fuel rods within a desired temperature during an irradiation test. The components and sensors in the test rig can be broken or malfunction owing to the flow-induced vibration. In this study, a coolant flow simulation system was developed to verify and confirm the soundness of components and sensors assembled in the test rig with a high flow rate of the coolant.

• Journal of the Korean Society for Railway
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• v.16 no.5
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• pp.394-401
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• 2013

Here we report the results of an experimental laboratory test to verify the applicability to railway bridges of a PSC I girder of which the upper flange thickness was increased to improve sectional performance. The thicker this flange is, the further upward the neutral axis is moved. If in this way the span length can be increased to 40m long, the bridge may be constructed with four girders instead of five. Therefore, construction cost could be lowered by reducing the weight of the long span structure due to increased sectional efficiency. It was also necessary to be certain that the dynamic performance of this relatively flexible structure would be applicable to railway bridges. Therefore numerical analysis, as well as static and dynamic tests, was carried out for a full-size PSC I girder. Based on these results, it was verified that the performance of the PSC I railway bridge satisfied the performance criteria of the design code.

• Fire Science and Engineering
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• v.26 no.6
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• pp.24-30
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• 2012

This study is on the method of the detection for flame and series arc which can be happened at poor contact point added a vibration in part of contact point of low voltage line. In general, the causes of electric fire are over current, short circuit, poor contact, ect. The over-current or short circuit among those causes is detected by measuring a instant current value, but poor contact is difficult to detect by measuring a excessive value of the voltage and current and a distortion of waveforms. And therefore, in this paper, it is studied on the optimal technique of the arc judgement using fuzzy logic and MDET (Multi Dimension Estimation Technique). And it carries out the simulation for arc detection and the experiment for controller and load test. In result, the controller and detection algoristhm, is classified with normal wave and abnormal arc wave without relation with each loads and so the controller can detect a series arc successfully.