• Journal of Welding and Joining
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• 제32권3호
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• pp.95-101
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• 2014

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).

• 한국대기환경학회지
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• 제28권1호
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• pp.39-51
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• 2012

Aerosol slurry samples were collected in 60-min interval using Korean Semi-continuous Elements in Aerosol Sampler (KSEAS) between May 19 and June 6, 2010 at an urban site of Gwangju. The $PM_{2.5}$ samples were collected with a flow rate of 16.7 L/min and particles are grown by condensation of water vapor in a condenser maintained at ${\sim}5^{\circ}C$ after saturation by direct injection of steam. The resulting droplets are collected in a liquid slurry with a airdroplet separator. Concentrations of 16 elements (Al, Fe, Mn, Ca, K, Cu, Zn, Pb, Cd, Cr, Ti, V, Ni, Co, As, Se) in the collected slurry samples were determined off-line by ICP-MS. KSEAS sample analysis encompassed the sampling periods for which 24-hr average elemental species concentrations were calculated for comparison with those derived from 24-hr integrated filter samples. Relationship between elemental species measured by two methods indicated high correlation coefficients (r), mostly greater than r of 0.80. However, we note that concentrations of Al, K, Ca, Mn, and Fe, which are often associated with crustal elemental particles, in the KSEAS samples, were substantially lower (1.4~11 times) than those found in the typical filter-based samples. This discrepancy is probably due to difficulties in transferring insoluble dust particles to the collection vials in the KSEAS. Temporal profiles of elemental concentrations indicate that some transient events in their concentrations are observed over the sampling periods. For the elemental species studied, atmospheric concentrations during the transient events increased by factors of 4 in Mn~80 in Zn, compared to their background levels. Principle component analyses were applied to the hourly KSEAS data sets to identify sources affecting the concentrations of the metal constituents observed. In this study, we conclude that hourly measurements for particle-bound elemental constituents were extremely useful for revealing the short-term variability in their concentrations and developing insights into their sources.

• 한국생산제조학회지
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• 제22권5호
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• pp.767-773
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• 2013

A high-pressure, high-pressure drop control valve, which transforms the power transfer of a system by reducing the inlet pressure of 345bartothe outlet pressure of 112bar, is a fundamental component in an offshore plant process. With the increasingly growing market share of the maritime industry, this valve has been expected to be a high-value-added product. This study not only analyzes the relation between pressure drop and fluid velocity in a trim by using fluid analysis, but also examines the possibility of cavitation in a valve in addition to the plot for the extension of lifespan. Based on the analysis results, the design and production method of the valve are established, and accordingly, performance evaluation is carried out. It is demonstrated that the pressure drop from 345bar to 112bar is more feasible in the presence of the trim, which can induce a continuous and diminutive pressure drop in order to prevent cavitation in a high-pressure drop control valve. Furthermore, despite the fluid velocity near a seatring being found to be over 30m/s, the lifespan of the valve is determined to be adequate considering the operation condition of a prototype valve of 80%.

• 한국항공우주학회지
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• 제35권3호
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• pp.248-252
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• 2007

본 연구는 공급계 관에서 극저온 연료의 일부가 기화될 경우에 로켓엔진이 지속적으로 작동될 수 있는지의 여부를 묻는 문제와 관련되어 있다. 유동장 내에 증기가 발생하는 것을 모사하는 실험의 결과분석으로 관내의 압력조건에서 극저온 유체의 온도가 포화온도보다 낮을 경우 발생된 증기가 완전히 응축될 수 있다는 것을 확인하였다. 극저온 유체의 정상유동에서 비평형 응축영역을 계산하기 위한 경험관계식을 무차원형태로 구하였고, 이 경험관계식이 실제적으로 활용 될 수 있는 분야를 제시하였다.

• 상하수도학회지
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• 제12권3호
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• pp.55-64
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• 1998

The degradation efficiency of chlorophenolic compounds in $TiO_2/H_2O_2$ combined system was compared with that of in $TiO_2$ sole system. As a result, the addition of hydrogen peroxide in photocatalytic oxidation reaction greatly enhanced the degradation efficiency of chlorophenolic compounds due to the availability of the hydroxyl radical formed on the $TiO_2$ surface. The hydrogen peroxide under UV illumination produces hydroxyl radicals that appear to be another source of hydroxyl radical formation. These results indicated the $TiO_2/H_2O_2$ combined system shows higher degradation efficiency than the $TiO_2$ sole system. Compared to another oxidation reaction, hydrogen peroxide assisted photocatalytic oxidation is more promising in practical aspect.

• 환경영향평가
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• 제10권1호
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• pp.9-19
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• 2001

An intensive watershed survey including water quality measurement of 6 times was carried out in order to find out the relationship between pollutant load and water quality in a small stream watershed where livestock wastewater is the main source of water pollution. The findings from the survey are as follows. 1) The number of livestock showed large disagreement among county office, myon, and insite survey. It is vital to check the data at the beginning of watershed survey. 2) The fluctuation of streamflow and water quality was so large depending on the day of measurement that it is essential to set up continuous telemetering system to get reliable data about delivery ratio of pollutants. 3) It was helpful for setting the priority of investigation to check water quality and quantity at several points along the stream after dividing the watershed into 5 drainage areas. 4) To control the livestock wastewater, especially in case of cows, it is necessary to have roof system and prevent overland flow from the ground. In case of pig farms, it is recommended to have public treatment system instead of private treatment system. The exact emission load of livestock wastewater was difficult to estimate, and requires more study.

• 한국시스템다이내믹스연구
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• 제14권1호
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• pp.5-29
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• 2013

This study tries to measure the direct and indirect effects of the Regional Strategic Industry (RSI) promotion projects in Chungbuk Province in Korea. In specific, it critically examines whether there exists policy consistency and connectivity between the hardware-oriented Stage I (2002~2007) and the software-centered Stage II (2008~2012) RSI promotion projects. Applying System Dynamics (SD) techniques, this study examines complex system characteristics of RSI promotion projects, all of which have been derived from the causal and stock-flow models and their simulated results. Major findings are as follows: Firstly, 'the continuous investment' is regarded as the most crucial policy leverage for the strategic industry promotion and regional economic growth. Secondly, without exceptions, the RSI promotion projects should switch their evaluation criteria to performance-oriented ones. Thirdly, in selecting their subprojects, the RSI promotion projects should pay due attention to evaluating technology value and marketability. Fourthly, it should put policy priority in strengthening cluster networking and interconnectivity among projects, inevitably supporting a selective number of virtuous network systems. Fifthly, auxiliary projects such as marketing, technology aid, and knowledge-based services should not be overlooked.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.552-557
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• 2006

Since the 20th century, the business of railway was invaded by the invention of airplanes and vehicles in the field of the transportation of passenger and commercial products, however, in the 21st century, the fervent development of a high-speed railway made possible the huge capacity of transporting passengers and commercial freight, so the railway industry is facing a new era of railway revolution. The 200 years old railway tradition includes the history of railway bridges built in areas of river, valley and metropolitan region and in that, the number of constructions of railway bridges that is composed of cable-stayed bridges is increasing as one of the most optimal bridges considering the quality of materials and the span of continuous-welded long rail. Thanks to the minimized effects of the fixed load on the stiffening girder section by delivering the fixed load which is applied to the pylon with the composition of elastic supporting-points by using cables and the effective structural system that can throughly resist extra loads in addition to fixed load, the long-extended span of a bridge becomes possible. In this structural system, the load that is applied to the stiffening girder section forms a flow pattern and in the process of these load delivery, there will be a necessity to examine the concentration of stress occurred in the cable-anchor system of the cable.

• 상하수도학회지
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• 제36권5호
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• pp.289-296
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• 2022

Mangyeong River and Dongjin River are highly dependent on external regions for domestic and agricultural water, and the agricultural water supply and use system of those rivers are very complicated. For smooth water supply, rivers are used as a supply system. Of the total river water use permits (as of 2019), agricultural water accounts for 97.5%, 80.4% in Mangyeong River and Dongjin River, respectively. The excessive intake of river water as agricultural purpose is causing the stream to dry out and to deteriorate the ecological health of the river. It is necessary to minimize the water use system that takes in and utilizes river water. In both rivers, the flow rate of agricultural drainage and the load of major water quality items that flowing into the main stream are similar to or higher than those of the major tributaries, indicating that management is necessary to improve the water quality of the river. It is necessary to understand the effect of agricultural drainage on river water quality by establishing a continuous monitoring system for the form of agricultural drainage.

• Coupled systems mechanics
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• 제9권2호
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• pp.111-123
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• 2020

Wastewater treatment plants (WWTPs) with activated sludge system are widely used throughout the most common technologies in the world. Most treatment plants require optimization of certain treatment processes using dynamic modeling. A lot of examples of dynamic simulations require reliable data base of diurnal variation of the inflow and typical concentrations of parameters such as Chemical Oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN), etc. Such detailed data are not available, which leads to problemsin the application of dynamic simulations. In many examples of plants, continuous flow measurements are only performed after the primary clarifier, whereas measurements from influent to the plant are missing, as is the case with the examples in this paper. In some cases, a simpler, faster and cheaper way can be applied to determine influent variations, such as the "HSG-Sim" method ("Hochschulgruppe Simulation"). "Hochschulgruppe Simulation" is a group of researchers from Germany, Austria, Switzerland, Luxembourg, Netherlands and Poland (see http://www.hsgsim.org). This paper presents a model for generating daily variations of inflow and concentration of municipal wastewater quality parameters, applied to several existing WWTPs in Bosnia and Herzegovina (B&H). The main goal of the applied method is to generate realistic influent data of the existing plants in B&H, in terms of flow and quality, without any prior comprehensive survey and measurements at the site. The examples of plants show the influence of overflow facilities on the dynamics of input flow and quality of wastewater, and a strong influence of the problems of the sewerage systems.