• Transactions of Materials Processing
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• v.22 no.1
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• pp.17-22
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• 2013

Tube hydroforming is a technology that utilizes hydraulic pressure to form a tube into desired shapes inside die cavities. Due to its advantages, such as weight reduction, increased strength, improved quality, and reduced tooling cost, single-layered tube hydroforming is widely used in industry. However in some special applications, it is necessary to produce multi-layered tubular components which have corrosion resistance, thermal resistance, conductivity, and abrasion resistance. In this study, a hollow forming process to fabricate a part from multi-layered tubes for structural purposes is proposed. To accomplish a successful hydroforming process, an analytical model that predicts optimal load path for various parameters such as tube material properties, thickness of tubes, diameter of holes and the number of holes was developed. Tubular hydroforming experiments to fabricate a hollow part were performed and the optimal loading path developed by the analytical model was successfully verified. The results show that the proposed hydroforming process can effectively produce hollow parts with multi-layered tube without defects such as wrinkling or fracture.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.17-22
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• 2009

계절에 따른 토양공극의 수리학적 변화를 파악하기 위해서 설마천 유역의 범륜사 독립사면과 광릉 원두부 소유역의 독립사면을 대상으로 장력침투실험을 실시하였다. 토양수분 확보에 신뢰를 받기위해서 TDR(Time Domain Reflectometry)및 현장에서 토양의 불포화 투수계수 측정이 가능한 장력침투계(Tension infiltrometer)를 이용하였다. 계절에 따른 자료수집을 위해서 2008년 3월 20일 부터 약 6주간격으로 10월 29일까지 5회에서 6회 토양수분 자료 및 토양장력침투 자료를 획득하였다. 획득한 자료를 이용하여 포화 및 불포화 수리전도도, 대공극 유효흐름분율(macropore flow), 대공극 유효부피분율을(effective macroporosity) 나타내었다. 분기별로 자료분석 결과 계절별 특성이 나타남을 알 수 있다. 수리전도도는 3월, 5월, 10월은 유사한 반면 6월과 7월 그리고 9월은 상대적으로 높았다. 이는 여름철에 공극 발달이 활발하다는 것을 의미한다. 선행토양수분은 수리전도도에 영향을 미치는 것으로 나타났다. 대공극의 발달은 삼림과 같은 복잡 경관에서는 강우사상에 따른 토양수분의 공간 분포 및 이송, 유출과정이 물순환에 영향을 미친다. 지형분석을 통한 공극의 흐름특성과 토양수분 유의성에 대하여 논의하였고, 대공극 변화에 밀접한 관계가 있는 식생과 그밖에 계절적으로 발달을 일으키는 요인을 모색 하였다. 본 연구는 계절에 따라 변하는 수리전도도를 기초로 하여 불포화대에서 토양공극의 수리학적 변화와 시공간적으로 침투흐름에 얼마나 영향을 주는가를 보여준다.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1924-1928
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• 2009

다중패커시스템은 격리된 어느 특정 구간의 지하수를 채수할 수 있으며 그 구간의 온도, 압력 등의 자료를 연속적으로 관측할 수 있어 이를 통해 각 구간별 수리전도도를 구할 수 있다. 심도별 수직적 지하수두는 지상에서 연결 롯드를 통해 압력 측정 센서를 해당 심도까지 내려 롯드에서 설치된 압력 측정용 장비에서 관측할 수 있으며, 다중패커시스템을 이용한 수리시험으로는 양수시험, 순간충격시험, 간섭시험 등이 있는데, 본 논문에서는 순간충격시험을 이용한 결과를 제시하였다. 도출된 구간별 수리전도도를 다중패커시스템을 설치하기 전 나공에서 이중 패커를 이용한 정압주입시험의 결과와 비교하여 보았다. 다중패커시스템을 통해 획득된 심도별 지하수두는 정수두 (hydro-static)상태의 일정한 경향성이 없이, 각 심도에 존재하는 투수성 구조에 영향을 보이고 있음을 알 수 있었으며, 이는 다수의 관측공을 통해 수평 방향의 수리경사를 산출함에 있어 관측공의 심도에 대한 충분한 고려가 있어야 한다고 판단된다. 또한, 다중패커시스템을 이용한 수리시험 결과를 나공 상태에서 이중 패커를 이용한 정압주입시험 결과에 대해 심도별 도출되는 수리전도도가 국지적으로 분포하는 투수성 구조에 영향으로 인해 투수량계수 (transmissivity)로 환산한 유효 투수계수로 비교하여 결정질 암반의 수리 특성으로 제안하는 것이 타당한 것으로 분석되었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1929-1933
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• 2009

수자원 수요가 급증함에 따라 단열 암반 대수층의 지하수를 개발해 이용하려는 연구가 많이 이루어지고 있다. 본 연구에서는 단열암반 대수층의 지하수 유동 특성을 알아보기 위해 한국원자력연구원 연구 지역 내에 NX 규격의 직경 78mm를 갖는 500m 심도의 심부시추공 (DB-01)을 굴착하였다. DB-01에 대한 시추공 단열조사 (BHTV) 및 시추코아 분석을 통해서 심부 시추공에 대한 예비 투수성 구조를 도출하였으며, 투수성이 큰 구조로 단열과 연결된 지점으로 판단되는 심도에 대해서 현장 수리시험을 수행하여, 결정질 암반의 투수성 구조에 대한 수리특성을 규명하였다. 그 결과를 분석하여 비교적 투수성이 큰 심도를 결정질 암반의 대수층이라 정의하였다. 수리특성이 비슷한 3가지의 그룹 중 3그룹은 투수계수도 가장 크고 단열빈도도 밀집되어 있는 것으로 나와 심부 200m에서 250m이하의 이 단열구간은 수자원으로 지하수의 활용이 가능하다고 여겨진다.

• Computers and Concrete
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• v.12 no.2
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• pp.151-167
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• 2013

Prediction of concrete properties is an important issue for structural engineers and different methods are developed for this purpose. Most of these methods are based on experimental data and use measured data for parameter estimation. Three typical methods of output estimation are Categorized Linear Regression (CLR), Multiple Linear Regression (MLR) and Artificial Neural Networks (ANN). In this paper a statistical cleansing method based on CLR is introduced. Afterwards, MLR and ANN approaches are also employed to predict the compressive strength of structural lightweight aggregate concrete. The valid input domain is briefly discussed. Finally the results of three prediction methods are compared to determine the most efficient method. The results indicate that despite higher accuracy of ANN, there are some limitations for the method. These limitations include high sensitivity of method to its valid input domain and selection criteria for determining the most efficient network.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.85-109
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• 2017

The paper presents the laboratory study of clayey soil stabilized with Pond ash (PA), Rice husk ash (RHA), cement and their combination used as stabilizers to develop and evaluate the performance of clayey soil. The effect of stabilizer types and dosage on fresh and mechanical properties is evaluated through compaction tests, unconfined compressive strength tests (UCS) and Split tensile strength tests (STS) performed on raw and stabilized soil. In addition SEM (scanning electron microscopy) and XRD (X-ray diffraction) tests were carried out on certain samples in order to study the surface morphological characteristics and hydraulic compounds, which were formed. Specimens were cured for 7, 14 and 28 days after which they were tested for unconfined compression tests and split tensile strength tests. The moisture and density curves indicate that addition of RHA and pond ash results in an increase in optimum moisture content (OMC) and decrease in maximum dry density (MDD). The replacement of clay with 40% PA, 10% RHA and 4% cement increased the strength (UCS and STS) of overall mix in comparison to the mixes where PA and RHA were used individually with cement. The improvement of 336% and 303% in UCS and STS respectively has been achieved with reference to clay only. Developed stabilized soil mixtures have shown satisfactory strength and can be used for low-cost construction to build road infrastructures.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.2
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• pp.157-166
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• 2012

Most of the roads are paved with impermeable materials such as asphalt concrete and cement concrete, and in the event of heavy rainfall, rainwater directly flows into river through a drainage hole on the pavement surface. This large quantity of rainwater directly spilled into the river frequently leads to the flooding of urban streams, damaging lowlands and the lower reaches of a river. In recent years there has been a great deal of ongoing research concerning water permeability and drainage in pavements. Accordingly, in this research, a porous polymer concrete was developed for permeable pavement by using unsaturated polyester resin as a binder, recycled aggregate as coarse aggregate, fly ash and blast furnace slag as filler, and its physical and mechanical properties were investigated. Also, 3 types of permeable polymer block by optimum mix design were developed and rainfall runoff reduction effects by permeability pavement using permeable polymer block were analyzed based on hydraulic experimental model. The infiltration volume, infiltration ratio, runoff initial time and runoff volume in permeability pavement with permeable polymer block of $300{\times}300{\times}80$ mm were evaluated for 50, 100 and 200mm/hr rainfall intensity.

• Structural Engineering and Mechanics
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• v.52 no.1
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• pp.35-49
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• 2014

This paper studies the behaviour of deteriorated reinforced concrete (RC) beams attacked by various forms of simulated acid rain. An artificial rainfall simulator was firstly designed and evaluated. Eleven RC beams ($120mm{\times}200mm{\times}1800mm$) were then constructed in the laboratory. Among them, one was acting as a reference beam and the others were subjected to three accelerated corrosion methods, including immersion, wetting-drying, and artificial rainfall methods, to simulate the attack of real acid rain. Acid solutions with pH levels of 1.5 and 2.5 were considered. Next, ultrasonic, scanning electron microscopy (SEM), dynamic, and three-point bending tests were performed to investigate the mechanical properties of concrete and flexural behaviour of the RC beams. It can be concluded that the designed artificial simulator can be effectively used to simulate the real acid rainfall. Both the immersion and wetting-drying methods magnify the effects of the real acid rainfall on the RC beams.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.13-21
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• 2002

A new method called S-SRICOS is proposed to predict the local scour depth around bridge piers. The S-SRICOS method is a simplified version of the SRICOS method which was developed to predict the scour depth versus time curve around bridge piers. The SRICOS method which considers the time effect based on the soil properties and the hydraulic parameters can handle a multi-flood hydrograph and multi-layer soil systems with the SRICOS program. An attempt was made to simplify the method to the point where only hand calculations would be required. The concept of the equivalent time was developed leer this purpose. The S-SROICOS method requires only 4 parameters such as pier width, design bridge life, design velocity corresponding to the design bridge life, and initial scour rate of the soil. The S-SRICOS method was verified against 55 cases of the scour depth results using the SRICOS method.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.89-98
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• 2005

Preliminary pile load tests for the design of large diameter drilled shaft were performed on two of reduced scale(D=1370mm) test piles. The maximum loads of 2350 tonf in each direction were applied using bi-directional hydraulic jacks(Osterberg Cell) at toe. Neither of the test piles yielded in terms of skin friction and end bearing. Comparisons of the test results with several methods that estimate pile capacity show that the method of Horvath and Kenney(1979) for skin friction and Zhang and Einstein(1998) for end bearing were most appropriate for the site. The test results were directly applied to pile design in case RQD of skin and toe was larger than that of the test pile. It is desirable, therefore, to consider not only unconfined compression strength but also rock mass properties(i.e. TCR, RQD) for skin friction and end bearing evaluation in the future.