• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.242-246
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• 2004

Effects of circumferentially local wall thinning on the fracture behavior of pipes were investigated by monotonic four-point bending. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area included an eroded ratio of d/t= 0.2, 0.5, 0.6, and 0.8, and an eroded length of I = 10 mm, 25 mm, and 120 mm. Fracture type could be classified into ovalization, local buckling, and crack initiation depending on the eroded length and eroded ratio. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors excepting failure due to cracking. It was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the eroded area.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.899-904
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• 2009

This paper presents the analysis result of load-transfer mechanism and pile movements associated with the development of frictional resistance to understand the engineering characteristics of micropile behavior. An field load tests were performed for two different types of micropiles and they are (i) thread bar reinforcement with D=50mm and (ii) hollow steel pipe reinforcement with $D_{out}$=82.5mm and $D_{in}$=60.5mm and wrapped with woven geotextile for post-grouting. The load test results indicated that micropiling with pressured grouting provided better load-transfer characteristics than micropiling with gravity grouting under both compressive and tensile loading conditions in that unit skin frictional resistance is well distributed along installation depth. The unit weight and unconfined compressive strength of cured grout were obtained for each piling method. The strength and unit weight of micropile with pressured grouting was higher than those with gravity grouting. The fact that load bearing quality with pressured grouting is better than that of gravity grouting could be attributed to the dense mutual adhesion between surrounding ground and pile due to pressurized grouting method and better grout quality.

• Structural Engineering and Mechanics
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• v.62 no.4
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• pp.381-389
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• 2017

In the present study, the advanced procedure has been proposed to estimate higher accuracy of embedment of pipes that are installed on soft clay seabed. Numerical simulation by OrcaFlex simulation code was performed to investigate dynamic seabed embedment, and two steps, i.e., static and dynamic analysis, were adopted. In total, four empirical curves were developed to estimate the seabed embedment including dynamic phenomena, i.e., behaviour of vessel, environmental condition, and behaviour of nonlinear soil. The obtained results were compared with existing methods (named general method) such as design code or guideline to examine the difference of seabed embedment for existing and advance methods. Once this process was carried out for each case, a diagram for estimating seabed embedment was established. The applicability of the proposed method was verified through applied examples with field survey data. This method will be very useful in predicting seabed embedment on soft clay, and the structural behaviours of installed subsea pipelines can be changed by the obtained seabed embedment in association with on-bottom stability, free span, and many others.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3041-3053
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• 1995

Cylindrical chokes are used widely as components of hydraulic equipments. The dynamic characteristics between flowrate and pressure drop through the cylindrical chokes were discussed by the frequency characteristics of the chokes. It was assumed no pressure recovery occurred near the downstream of the choke. The pulsating jetflow from the outlet of cylindrical chokes show very complex behaviours which are quite different from the steady jet flow but it's not clarified quantitatively. In order to utilize the chokes as a flowmeter, it is indispensable to discuss the estimation of the dynamics of pressure drop in the downstream jetflow region of cylindrical chokes. In this experimental study, it is clarified that the reattachment length depended on pressure wave is compared with it depended on velocity wave. A pulsating flow is verified by visualization method. In the present study, the flow characteristic variables of laminar pulsating flow are investigated analytically and experimentally in a circular pipe. Characteristic parameters of the ratios of inertia(.PHI.$_{t,1}$) and viscous(.PHI.$_{z,1}$) term to pressure term are introduced to describe the flow pattern of laminar pulsating flow. flow.low.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.493-498
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• 2008

Particles or deposit formed by corrosion of the pipe material bring about bad influences on the heating systems with inconvenience, energy loss and so on. In order to obtain the non-corrosive environments, the circulation hot water should properly be treated in several ways to satisfy one or more conditions of the followings: suitable pH-level, low hardness, low oxygen content, low conductivity, low level of chlorides and sulphur compounds and low level of solid particles. This experimental study was carried out to develope the new guidelines on the optimal water quality and directions for water quality management in heating systems. As results, it was recommended that the heating water be maintained pH-level not less than 8, hardness contents as $CaCO_3$ no more than 50 mg/L, turbidity no more than 10 NTU and T-Fe contents 1 mg/L below.

• Proceedings of the Korea Society for Simulation Conference
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• 2005.11a
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• pp.130-137
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• 2005

본 논문은 심장이 수축$\cdot$이완함에 따라 그 형태와 위치가 변하는 관상동맥의 구조와 그 움직임을 사실적으로 표현하기 위한 매개변수적 모델링 기법을 제안한다. 완성된 모델은 관상동맥의 움직임을 관찰함으로써 심장질환 판단에 도움을 주고, 심장시술 시뮬레이션 및 시술계획수립에 사용될 수 있다. 매개변수적 기법으로 생성된 모델은 메쉬 정점의 인덱스만으로 모델간 매칭을 위한 대응점을 찾을 수 있으므로, 시간대별로 달라지는 정점의 위치를 쉽게 추적함으로써 모델의 움직임을 표현할 수 있다. 그러나 이러한 기법으로 생성된 모델은 분리, 접합 등의 변형조작이 어렵고, 트리형태 객체에 적용하기 힘든 단점이 있다. 본 논문에서는 이를 극복하기 위해 분할된 혈관영역의 골격데이타에서 찾아낸 분기점을 중심으로 Generalized Cylinder를 이용하여 실린더 형태의 각 혈관세그먼트를 모델링 한 후, 분기영역을 3개의 하프파이프(half pipe)와 2개의 삼각형 패치로 연결하여 모델링하였다. 완성된 모델은 다시점 관상동맥데이터에 적용하였고, 각 시점에서 구해진 정점의 위치를 선형보간함으로써 부드러운 혈관의 움직임을 나타내었다.

• Nuclear Engineering and Technology
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• v.32 no.6
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• pp.618-635
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• 2000

A total of 17 experimental data for the onset of slugging, which is assumed to be the precursor of the condensation-induced waterhammer (CIWH), have been obtained for various How rates of water Incorporating the most recent correlations of interfacial heat transfer and friction factor developed for a circular geometry and using an improved criterion of transition from stratified to a slug flow, two existing analytical models to predict lower and upper bounds for CIWH have been upgraded. Applicability of the present as well as existing CIWH models has been tested by comparison with two sets of CIWH data. The result of this comparison shows that the applicability of the present as well as existing models is reasonably good. Based on the present models for CIWH, a computer code entitled as“KAIST-CIWH”has been developed and sample guide charts to find CIWH free regions for a given combination of major flow parameters in a long horizontal pipe have been presented along with the results of parametric studies of major parameters (D, P, $T_{f,in}$, and L/D) on the critical inlet water flow rate（$W_{f,in}_crit$ for both lower and upper bounds. In addition, two simple formulas for lower and upper bounds that can be used in an emergency for quick results have been presented.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.1
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• pp.33-47
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• 1992

Experimental investigation on the performance of a heat pump system using refrigerant mixtures is done. The condenser and the evaporator are double pipe heat exchangers of counter flow type and the compressor is driven by a variable speed motor. The refrigerant mixture used in the experiment is R22/R142b. Experiments are performed by changing the compressor speed, composition on ratio of mixture, and the average temperatures of condenser and evaporator. The compressor work, heating capacity and the coefficient of performance are calculated. Results show that the heating capacity can be changed by varying the mass flow rate of refrigerant mixtures to meet the heating load. It is shown that the capacity control by changing the composition ratio is more effective than by changing the compressor speed. Under the condition where the external conditions are fixed and the heating loads are equal, the coefficient of performance has its maximum value near 50 : 50 mass fraction of the refrigerant mixture in this study.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.136-141
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• 2009

Considerable part of energy consumption is occurred by through buildings. Especially, Lighting energy consumption is most part of one in building. There is very various ways and systems for saving lighting energy. In method, It can be divided Passive Daylighting System and Active Daylighting System. Louver, Screen and use of window's character is representative ways of passive system. Reflection mirror, optical pipe and optical fiber is representative method of active system. Introducing day light on which place can't be introduced day light by typical method is important advantage of active system. Except introducing day lighting methods, efficient lighting management system can save lighting energy. It called lighting automation system. Representatively, Occupancy-related automation and Brightness-related automation system is that. According to occupancy and introducing daylighting level properly operate lamp's intensity of illumination that can save lots of energy. Though Introducing daylighting method, effective lighting system we can get proper intensity of illuminance level and energy saving.

• Proceedings of the KIEE Conference
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• 2003.11a
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• pp.379-381
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• 2003

The sharing of common corridors by electric power transmission lines and pipelines is becoming more common place. However, such corridor sharing can result in undesired coupling of electromagnetic energy from the power lines to the near facilities. This causes induced voltages on underground metallic pipelines due to the power line currents. This could cause AC corrosion in the pipeline, which could in turn lead to disastrous accidents, such as gas explosion or oil leakage. This paper investigates for the limitation of induced voltage on the buried metal structures which is used in the inside and outside of the country. And then we measure the earth resistance and leakage current of 22.9kV distribution lines and pipe to soil potential of near pipelines in Seoul Korea. Hereby we can see the leakage current flowing through the earthing electrode have an effect on near pipelines.