• 한국재료학회지
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• 제29권10호
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• pp.617-622
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• 2019

In order to develop a process for manufacturing a composite structure of an intermetallic compound foam and a hollow material, the firing and pore form of the Al-Ni precursor in a steel pipe are investigated. When the Al-Ni precursor is foamed in a hollow pipe, if the temperature distribution inside the precursor is uneven, the pore shape distribution becomes uneven. In free foaming, no anisotropy is observed in the foaming direction and the pore shape is isotropic. However, in the hollow pipe, the pipe expands in the pipe axis direction and fills the pipe. The interfacial adhesion between $Al_3Ni$ foam and steel pipe is excellent, and interfacial pore and reaction layer are not observed by SEM. In free foaming, the porosity is 90 %, but it decreases to about 80 % in the foam in the pipe. In the pipe foaming, most of the pore shape appears elongated in the pipe direction in the vicinity of the pipe, and this tendency is more remarkable when the inside pipe diameter is small. It can be seen that the pore size of the foam sample in the pipe is larger than that of free foam, because coarse pores remain after solidification of the foam because the shape of the foam is supported by the pipe. The vertical/horizontal length ratio expands along the pipe axis direction by foaming in the pipe, and therefore circularity is reduced.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.23-26
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• 2008

In order to examine the deformation characteristics of Al circular pipe underthe biaxial compression, the horizontal biaxial compression die for the experiment was manufactured. From this, in the various compressive strain rate (1 mm/min. ${\sim}$ 400 mm/min.)conditions, the circular pipes, which were made by Al materials, were investigated based on the properties change of cross section area, punch load and deformation behavior. The tensile and compressive strains were evaluated from micro Vickers hardness tester. From these results, the punch load and deformation characteristic of Al circular pipes were highly changed in the compressive strain rate about 200 mm/min. The Al circular pipes had the tendency that the punch load decreased with increasing the compressive strain rate. In addition, following as the change of the shape and position of neutral axis due to the deformation proceeding of the circular pipe, the special point of the internal circular pipe at maximum load showed the maximum deformation strain and the maximum measured hardness value. The CAE (computer aided engineering) simulation using Deform-2D program was performed on the circular pipe in order to know and verify the exact compressive deformation behavior. From these results, the experimentally measured results were reasonably in good agreement with the simulation results.

• 디지털콘텐츠학회 논문지
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• 제18권7호
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• pp.1387-1391
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• 2017

절단 파워 예측은 가공 툴 또는 공작기계의 최적 설계를 가능하게 하므로 기술 개발에 소요되는 시간과 비용을 줄일 수 있다. 이러한 이유로 정확한 절단파워 예측은 설계과정에서 매우 중요한 부분이다. 본 연구에서는 파이프 절단 파워를 이론적으로 예측하고 실험을 통해 검증한다. 우선, slotting 절단 파워 계산식을 사용하여 파이프의 절단 파워를 예측한다. 다음으로 파이프 절단기로 파이프를 절단하는 실험을 진행하며, 파이프를 절단하는 동안 모터에서 소비하는 파워를 embedded 소프트웨어인 Labview로 측정한다. 그리고 이론으로 계산한 절단파워와 실험으로 측정한 절단파워를 비교하여 정확성을 검증한다. 본 연구에서 사용한 파이프의 재질은 SUS304와 AL6N01이다. 그리고 본 연구에서는 실험을 통해 AL6N01 재질의 specific power 값을 구하였으며 추후 이 재질의 절단 및 절삭파워를 예측하고 최적의 가공기 및 툴을 설계하는데 이 값을 활용할 수 있다.

• 한국정밀공학회지
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• 제20권6호
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• pp.130-137
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• 2003

The pipe of CFRP for bicycle frame is designed and made for light weight of bicycle and then its suitability to bicycle frame is verified by comparing the other material i.e. steel, Cr-Mo steel, Al alloy pipe for bicycle frame. The pipe of CFRP is laminated to [0/$\pm$45]$_T$ and made by tape winding method and then its degree of light weight is evaluated by comparing the other pipes which is made by steel etc.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1200-1205
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• 2014

The effect of nanofluids on the heat transfer performance of a pulsating heat pipe has been experimentally investigated. Water-based diamond nanofluid and aluminium oxide ($Al_2O_3$) nanofluid were tested in the concentration range of 0.5-5%. The pulsating heat pipe was constructed using clear Pyrex tubes of 1.85 mm in inner diameter in order to visualize the pulsating action. The total number of turns was eight each for heated and cooled parts. The supply temperatures of heating water and cooling water were fixed at $80^{\circ}C$ and $25^{\circ}C$ respectively. The liquid charging ratio of the nanofluid was 50-70%. The test results showed that the case of 5% concentration of diamond nanofluid showed 18% increase in heat transfer rate compared to pure water. The case of 0.5% concentration of $Al_2O_3$ nanofluid showed 24% increase in heat transfer rate compared to pure water. But the increase of $Al_2O_3$ nanofluid concentration up to 3% did not show further enhancement in heat transfer. It is also observed that the deposited nanoparticles on the tube wall played a major role in enhanced evaporation of working fluid and this could be the reason for the enhancement of heat transfer by a nanofluid, not the enhanced thermal conductivity of the nanofluid.

• Nuclear Engineering and Technology
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• 제54권5호
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• pp.1588-1596
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• 2022

In the nuclear power plants, stainless steel is widely used for fabrication of various components such as piping and pipe fittings. These piping components are subjected to cyclic loading due to start up and shut down of the nuclear power plants. The application of cyclic loading may lead to initiation of crack at stress raiser locations such as nozzle to piping connection, crown of piping bends etc. of the piping system. Crack initiation can also take place from the flaws which have gone unnoticed during manufacturing. Therefore, prediction of crack initiation life would help in decision making with respect to plant operational life. The primary objective of the present study is to compile various analytical models to predict the crack initiation life of the pipes with notch. Here notch simulates the stress raisers in the piping system. As a part of the study, Coffin-Manson equations have been benchmarked to predict the crack initiation life of pipe with notch. Analytical models proposed by Zheng et al. [1], Singh et al. [2], Yang Dong et al. [25], Masayuki et al. [33] and Liu et al. [3] were compiled to predict the crack initiation life of SA312 Type 304LN stainless steel pipe with notch under fatigue loading. Tensile and low cycle fatigue properties were evaluated for the same lot of SA312 Type 304LN stainless steel as that of pipe test. The predicted crack initiation lives by different models were compared with the experimental results of three pipes under different frequencies and loading conditions. It was observed that the predicted crack initiation life is in very good agreement with experimental results with maximum difference of ±10.0%.

• 대한기계학회논문집B
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• 제39권7호
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• pp.599-607
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• 2015

본 연구에서는 나노유체의 유동학 특성을 반영한 히트파이프 열적특성을 연구하였다. $Al_2O_3$와 CuO 나노입자를 적용한 나노유체를 작동유체로 하여 나노입자 부피비와 응집도에 대한 히트파이프 성능을 확인하였다. 나노입자의 부피비와 응집도가 증가할수록 점성과 열전도도는 증가하는 것으로 나타났으며 두 인자는 히트파이프 성능에 영향을 주었다. 나노입자응집이 없는 경우에는 나노입자의 부피비 증가가 모세관압력한계 성능을 향상시켰지만 응집도가 증가하면 입자부피비가 증가해도 모세관압력한계가 감소했다. 그리고 나노입자의 열전도도, 부피비, 응집도에 대한 히트파이프 열저항을 분석하였다. 히트파이프의 투과율이 높을수록 최대열수송량은 입자부피비에 미치는 영향이 컸으며 3차원 그래프를 통해 윅 특성에 대한 최적화된 나노입자부피비를 확인하였다.

• 상하수도학회지
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• 제16권6호
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• pp.710-716
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• 2002

A General Pipe Break Prediction Model that incorporates linear and exponential models in its form is developed. The model is capable of fitting pipe break trends that have linear, exponential or in between of linear and exponential trend by using a weighting factor. The weighting factor is adjusted to obtain a best model that minimizes the sum of squared errors of the model. The model essentially plots a best curve (or a line) passing through "cumulative number of pipe breaks" versus "break times since installation of a pipe" data points. Therefore, it prevents over-predicting future number of pipe breaks compared to the conventional exponential model. The optimal replacement time equation is derived by using the Threshold Break Rate equation by Loganathan et al. (2002).

• Steel and Composite Structures
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• 제30권3호
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• pp.281-292
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• 2019

In this paper, analysis of critical fluid velocity and heat transfer in the nanocomposite pipes conveying nanofluid is presented. The pipe is reinforced by carbon nanotubes (CNTs) and the fluid is mixed by $AL_2O_3$ nanoparticles. The material properties of the nanocomposite pipe and nanofluid are considered temperature-dependent and the structure is subjected to magnetic field. The forces of fluid viscosity and turbulent pressure are obtained using momentum equations of fluid. Based on energy balance, the convection of inner and outer fluids, conduction of pipe and heat generation are considered. For mathematical modeling of the nanocomposite pipes, the first order shear deformation theory (FSDT) and energy method are used. Utilizing the Lagrange method, the coupled pipe-nanofluid motion equations are derived. Applying a semi-analytical method, the motion equations are solved for obtaining the critical fluid velocity and critical Reynolds and Nusselt numbers. The effects of CNTs volume percent, $AL_2O_3$ nanoparticles volume percent, length to radius ratio of the pipe and shell surface roughness were shown on the critical fluid velocity, critical Reynolds and Nusselt numbers. The results are validated with other published work which shows the accuracy of obtained results of this work. Numerical results indicate that for heat generation of $Q=10MW/m^3$, adding 6% $AL_2O_3$ nanoparticles to the fluid increases 20% the critical fluid velocity and 15% the Nusselt number which can be useful for heat exchangers.

• 한국수자원학회논문집
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• 제42권7호
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• pp.525-535
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• 2009

본 연구에서는 상수관망에서 개별적으로 노후도가 심하여 개량이 필요한 구간을 보다 정확하게 구분하기 위해 새로운 개별관로 정의 방법이 개발되었다. 적절한 관로 최소구성성분 길이를 결정하기 위하여 여러 가지 관로 최소구성성분 길이에 대한 평균 누적파손횟수경사선의 분산값을 비교하여 가장 큰 분산값을 나타내는 관로 최소구성성분 길이인 4 m 를 연구대상 지역의 상수관망에 적용하였으며 관로 ID는 39개로 구분되어졌다. 관로의 경제적 최적교체 시기는 한계파손율과 관로의 파손경향모형을 이용하여 결정되었는데, 각 관로 ID에 대하여 관로의 선형적 파손경향, 지수적 파손경향 또는 선형과 지수형 사이에 있는 파손경향 모두에 적용될 수 있는 General Pipe Break Prediction Model(Park and Loganathan, 2002)과 수정된 시간척도를 이용한 ROCOF(Park et al., 2007)를 적용하여 연구대상 상수관망의 최적교체시기를 산정 및 분석하였다. ROCOF 모형화 과정에서 대수-선형과 와이블 ROCOF를 적용 후 최대로그우도 추정값을 비교하여 최대로그우도가 큰 값을 가지는 ROCOF를 각 관로 ID의 ROCOF로 사용하였다. 관로파손으로 인한 사회적 비용이 관로의 최적교체시기에 미치는 영향도 분석되었다.