• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1323-1329
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• 1994

Tape casting and lamination were used to produce heterogeneous laminates with alternating layers of different porosity and homogeneous laminates with component layers of the same porosity. The pore structure was investigated for heterogeneous laminates, and bend strength was measured for comparison with that of homogeneous laminates. For a reference, strength measurement was made for the porous body fabricated by sintering samples dry-pressed at low pressure with spray-dried granules. Strength increase, in the range 50~120 MPa, was achieved in the presence of the surface dense layer, while extensive delamination, presumably responsible for enhanced fracture toughness, took place through the internal porous layer.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.545-550
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• 1991

Recently, the use of robots for painting operations has received much attention, as it is a powerful means for automation and quality improvement. Collision-avoidance is a key issue in the path planning for painting operations. In this paper, we develop a computationally efficient algorithm for the generation of collision-free path for two types of motion: a) Gross motion when the robot approaches the painting area, and b) Fine motion while spraying the surface. The former is a typical collision-avoidance problem, but the latter calls for special attention as the painting mechanics has to be incorporated into path planning. The developed algorithm is applied for the internal coating of the car body whose structure is the major source of collision.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.127-138
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• 2016

Diesel vehicles should be equipped with urea-selective catalytic reduction(SCR) system as a high-performance catalyst, in order to reduce harmful nitrogen oxide emissions. In this study, a three-dimensional Eulerian-Lagrangian CFD analysis was used to numerically predict the multiphase flow characteristics of the urea-SCR system, coupled with the chemical reactions of the system's transport phenomena. Then, the numerical spray structure was modified by comparing the results with the measured values from spray visualization, such as the injection velocity, penentration length, spray radius, and sauter mean diameter. In addition, the analysis results were verified by comparison with the removal efficiency of the nitrogen oxide emissions during engine and chassis tests, resulting in accuracy of the relative error of less than 5%. Finally, a verified CFD analysis was used to calculate the interanl flow of the urea-SCR system, thereby analyzing the characteristics of pressure drop and velocity increase, and predicting the uniformity index and overdistribution positions of ammonia.

• Journal of Digestive Cancer Research
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• v.2 no.1
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• pp.1-4
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• 2014

Palliative care for cancer aims to relieve the discomfort and pain from the cancer itself and associated conditions. Gastrointestinal cancers originate from the tube like structure of gastrointestinal tract and cause complications such as obstruction, bleeding, adhesion, invasion, and perforation to adjacent organ. Recent advances in interventional endoscopy enables endoscopy physicians to do safe and effective care for gastrointestinal cancer patients. Endoscopic palliation includes stent, hemostasis, nutritional support and targeted drug delivery. Self expandable metallic stent is one of the most important modalities in gastrointestinal palliation. Through the endoscopy or over the wire pre-placed by endoscopy, stents restore the gastrointestinal luminal patency and relieve the obstructive condition. Endoscopic hemostasis is another important palliation in gastrointestinal cancer patients. Epinephrine injection, argon plasma coagulation and thermal cauterization are usual modalities for hemostasis. Histoacryl glue and fibrin glue are also available. Hemostatic nanopowder spray is newly reported effective in benign disease and is supposed to be effective also in cancer bleeding. Enteral feeding tubes including gastro- or jejunostomy and nosoduodenal tubes are placed by using endoscopic guidance. Enteral feeding tubes role as the route of easily absorbable or semi-digested nutrients and effectively maintain both patients calorie requirements and gut microenvironment. Photodynamic therapy is the one of the outstanding medical employments of photo-physics. Especially for superficial cancers in esophagus, photodynamic therapy is very useful in cancer removal and maintaining organ structure. In biliary neoplasm, photodynamic therapy is well known to be effective in cancer ablation and biliary ductal patency restoration. Targeted drug delivery is the lastest issue in palliative endoscopy. Debates and questions are still on the table. In this article, the role of endoscopic interventions in palliative care for the gastrointestinal tumors will be thoroughly reviewed.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.211-219
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• 2017

The spray-applied waterproofing membrane is installed on shotcrete or concrete surface to make impermeable layer with 3-5 mm thick for the purpose of waterproofing. This study aims to determine the internal structure of a spray-applied waterproofing membrane including pores by using X-ray CT technique. Before obtaining X-ray images of the membrane specimens, a waterproof performance test was performed on the membrane specimens with a water pressure of 500 kPa for 28 days. Results show that the movement of moisture is made through micropores. This is based on the fact that the large pores inside the membrane are not saturated and the degrees of saturation of the micropores are high. X-ray image is effective for determining the pore size distribution and whether the membrane with pores contains the water However, it is necessary to pay attention to the determination of water content, since water content may vary depending on the threshold value of X-ray image analysis applied to calculate the water content.

• Journal of ILASS-Korea
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• v.16 no.4
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• pp.167-175
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• 2011

The HCCI engines have been known with high efficiency and low pollution and can be actualized as the new internal combustion engines. However, As for(??) the ignition and combustion depend strongly on the oxidation reaction of the fuel, so it is difficult to control auto-ignition timing and combustion duration. Purpose of this paper is creating the database for development of multi-dimensional simulation and investigating the influence of different molecular structure. In this research, the effect of n-heptane mole ratio in fuel (XnH) on the ignition delay from homogeneous charge compression ignition(HCCI) has been investigated experimentally. By varying the XnH, it was possible to ascertain whether or not XnH is the main resource of ignition delay. Additionally, the information on equivalence ratio for varying XnH was obtained. The tests were performed on a RCM (Rapid Compression Machine) fueled with n-heptane and iso-octane. The results showed that decreasing XnH (100, 30, 20, 10,0), the ignition delays of low temperature reaction (tL) and high temperature reaction (tH) is longer. And the temperature of reaction increases by about 30K. n-heptane partial equivalence ratio (fnH) affect on tL.and TL. When ${\phi}$nH was increased as a certain value, tL was decreased and TL was increased.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.479-484
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• 2001

고순도 알루미나 분말에 소결조제로서 MgO를 0ppm 및 500ppm 첨가하여 열분무건조기를 사용하여 준비한 과립을 80$0^{\circ}C$에서 하소를 함으로써 얻어진 과립으로 제작한 소결체의 MgO 첨가량에 따른 미세구조와 꺾임강도에 미치는 영향을 고찰하였다. 또한 시편두께를 50$mu extrm{m}$의 박편으로 가공하여 투광법으로 내부구조도 관찰하였다. MgO를 500ppm 첨가하여 제작한 과립을 180 MPa의 냉간정수압성형성 후 1$600^{\circ}C$에서 소결한 소결체는 상대밀도가 100%에 도달하였고 균일한 결정립성장의 치밀한 미세구조를 나타내었다. MgO를 500ppm 첨가한 시편의 4점 꺾임강도 또한 각 소결온도에서 MgO를 9ppm 첨가한 시편보다 23%-32%정도 높은 강도를 나타내었으며, 특히 소결온도 1$600^{\circ}C$에서는 꺾임강도가 501MPa 그리고 weibull 계수가 20의 고강도이면서 신뢰성이 높은 알루미나 소결체가 얻어졌다. 본 연구에서는 weibull 계수의 값이 높은 시편일수록 내부구조의 결함크기가 작고 이 작은 결함이 시편내부에 균일하게 분포되어 있음을 확인할 수 있었다.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.125-130
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• 2001

Experimental and analytical researches have been conducted on the twin-fluid atomizers for better droplet breakup during the past decades. But, the studies on the disintegration mechanism still present a great challenge to understand the drop behavior and breakup structure. In an effort to describe the aerodynamic behavior of the sprays issuing from the internal mixing counter-swirling nozzle, the spatial distribution of axial (U) radial (V) and tangential (W) components of droplet velocities are investigated across the radial distance at several axial locations of Z=30, 50, 80, 120 and 170mm, respectively. Experiments were conducted for the liquid flow rates which was kept constant at 7.95 g/s and the air injection pressures were varied from 20 kPa to 140 kPa. Counter-swirling internal mixing nozzles manufactured at angles of $15^{\circ},\;30^{\circ},\;45^{\circ}$ and $60^{\circ}$ the central axis with axi-symmetric tangential-drilled holes was considered. The distributions of velocities and turbulence intensities are comparatively analyzed. PDPA is installed to specify spray flows, which have been conducted along the axial downstream distance from the nozzle exit. Ten thousand of sampling data was collected at each point with time limits of 30 second. 3-D automatic traversing system is used to control the exact measurement. It is observed that the sprays with all swirl angle have the maximum SMD for on air injection pressure of 20 kPa and 140 kPa with centerline, respectively. The nozzle with swirl angle of $60^{\circ}$ has vest performance.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.84-93
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• 2022

To implement carbon-neutrality in transportation sectors until 2050, hydrogen is considered a promising fuel for internal combustion engines because hydrogen does not contain carbon itself. Although hydrogen does not emit CO₂ emission from its combustion process, the low energy density in a volume unit hinders the adoption of hydrogen. Therefore, the understanding of hydrogen jet behavior and measurement of equivalence ratio must be conducted to completely implement the high-pressure hydrogen direct injection. The main objective of this research is feasibility test of hydrogen local equivalence ratio measurement by laser-induced breakdown spectroscopy (LIBs). To visualize the macroscopic structure of hydrogen jet, high-speed schlieren imaging was conducted. Moreover, LIBs has been adopted to validate the feasibility of hydrogen local equivalence ratio measurement. The hydrogen injection pressure was varied from 4 MPa to 8 MPa and injected in a constant volume chamber where the ambient pressure was 0.5 MPa. The increased injection pressure extends the vertical penetration of hydrogen jet. Due to the higher momentum supply when the injection pressure is high, the hydrogen has easily diffused in all directions. As the laser trigger timing has delayed, the low hydrogen atomic emission was detected due to the longer mixture formation time. Based on equivalence ratio measurement results, LIBs could be applied as a methodology for hydrogen local equivalence ratio measurement.

• Journal of Energy Engineering
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• v.24 no.3
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• pp.96-108
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• 2015

A passive containment cooling system has been designed to remove the heat inside a containment during accidents without external power supply. In this work, the PCCS was introduced in the APR1400 plant to replace the containment spray system and, then, the thermal-hydraulic performance of the PCCS was analyzed using the system thermal-hydraulic computer code, MARS. A double-ended cold-leg break accident, which is known to induce the maximum pressure in the containment, is simulated, where the thermal hydraulics of the PCCS, the reactor coolant system, and the containment are simultaneously simulated. The results of the calculations showed that the PCCS can replace the existing spray system and that the containment building and its internal structure also play a very important role for the heat removal during the accident. Some sensitivity calculations were carried out to evaluate the model uncertainty and the effects of design parameters. The limitations of the PCCS are also discussed.