• Fire Science and Engineering
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• v.24 no.3
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• pp.93-98
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• 2010

Even though the sprinkler system is a essential fire suppression system, the design engineers do not fully understand the concept of design area which sprinklers operate. They frequently made a mistake to form design area and calculate it. The shape of design area is a square or a rectangle which branch side line is a little longer than the cross main side. NFPA demands to lengthen the branch side to 1.2 times than the cross main side and FM demands 1.4 times. The longer the branch side at the same design area is, the bigger the water quantity and pressure is. At the results of hydraulic calculation of design areas, when the branch side is longer 1.2 times, the water quantity became 4.6% bigger than exact square and the pressure came to 4.67% bigger. When it is longer 1.4 times, the water quantity and the pressure are bigger 7.52%, 14.51%. Therefore, the sprinkler design engineers should follow the general rule of design area, exact square or rectangle which length along the branch line is a little longer than length along the cross main, to design more stable system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1163-1168
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• 2011

Compared with the spark-ignition gasoline engine, the compression-ignition diesel engine has reduced fuel consumption due to its higher thermal efficiency. In addition, this reduction in the fuel consumption also leads to a reduction in $CO_2$ emission. Diesel engines do not require spark-ignition systems, which makes them less technically complex. Thus, diesel engines are very suitable target engines for using biofuels with high cetane numbers. In this study, the spray characteristics of biofuels such as vegetable jatropha oil and soybean oil were analyzed and compared with those of diesel oil. The injection pressures and blend ratios of jatropha oil and diesel oil (BD3, BD5, and BD20) were used as the main parameters. The injection pressures were set to 500, 1000, 1500, and 1600 bar. The injection duration was set to $500{\mu}s$. Consequently, it was found that there is no significant difference in the characteristics of the spray behavior (spray angle) in response to changes in the blend ratio of the biodiesel or changes in the injection pressure. However, at higher injection pressures, the spray angle decreased slightly.

• Journal of Biomedical Engineering Research
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• v.20 no.5
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• pp.559-566
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• 1999

환자의 기능평가를 위하여 중요한 자세균형의 유지는 압력중심(COP) 의 동요 신호를 직접 연속적으로 계측함으로써 가능하다. COP 신호로부터 다양한 종류의 자세안정도지표를 산출할 수 있으나 임상적으로 유용한 최소한의 지표종류로는 규명된 바 없다. 이에 본 연구에서는 인체가 서있는 상태의 정적자세를 유지할 때 압력중심 신호로부터 자세안정도지표를 산출하여 분석함으로써 임상적 유용성이 가장 큰 지표의 종류를 결정하고자 하였다. 양발을 편안히 벌리거나 (FS), 모두 모으거나(FT), 한쪽발 만으로(RL, LL)서있는 자세에 대해서 양쪽 눈을 뜨거나(EO) 감은(EC)8가지 정적자세를 취하며 30초간 자세균형을 유지시켰다. 자세형태에 따른 안정도의 척도로서 신체가 지면을 차지하는 면적(S)을 사용하였다. 자세안정도지표로서 1)position deviation, 2) position turn 3) velocity의 3가지로 분류할 수 있는 18가지 지표를 설정하였다. 피검자는 20, 30, 40 ,50 대 정상인을 연령대 별로 각각 남·녀 5명씩 고르게 총 40명을 선정하여 실험하였다. 자세안정도지표 모두가 S와 비교적 높은 유의한 상관관계를 보인 바 인을 연령대 별로 각각 남·녀 5명씩 고르게 총 40명을 선정하여 실험하였다. 자세안정도지표 모두가 S와 비교적 높은 유의한 상관관계를 보인바 (상관계수=0.6∼0.8, P<0.0001), S가 자세형태를 정량화 할 수 있음을 입증하였다. 모든 지표들에 있어서 시각의 영향이 뚜렷하였으며 특히 자세가 불안해질수록 상대적으로 시각의 영향이 두드러졌다. 그러나 시각의 영향의 지표들간의 차이는 없었다. 반면 노화(연령증가)에 따른 안정도지표의 변화는 미미하였으며 위의 3가지 안정도지표분류 중 position deviation 지표만이 통계적으로 유의한(P<0.05) 상관관계를 보였다. 따라서 정적자세유지시 안정도지표로는 position deviation 지표들이 가장 예민함을 알 수 있었다. 그러나 position deviation 지표들과 연령과의 상관계수는 0.5이하로서 매우 느슨한 상관관계를 보였으며, 연령증가에 따른 자제불안정도의 증가도 매우 작아서 그 임상적 응용가능성은 의문시되었다. 또한 위에서 제시한 3가지의 분류의 지표중 position turn 과 velocity 지표의 의미에 관해서는 향후 심층적인 연구가 필요한 것으로 판단되었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.17-25
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• 2019

An intake of Aircraft becomes S-shaped geometry due to spatial limitation or procuring survivability. But curvature of the S-shaped geometry makes secondary flow or flow separation which is the cause of non-uniform pressure distribution. In this study, boundary layer suction is applied to RAE M 2129 S-Duct by attaching sub duct. Design variable is suction location and angle. A mass flow rate drawn out by suction at the sub duct outlet is constant over every model. A grid dependency test was conducted to verify validity of computation. The comparison among the CFD (Computation Fluid Dynamics), ARA experimental result, and ARA computation result of non-dimensional pressure distribution on the Port side and Starboard Side confirmed the validity of CFD. In this study, Distortion Coefficient was used for evaluating aerodynamic performance of S-Duct. The analysis, which was about flow separation, vortex, mass flow rate distribution, and pressure distribution were also investigated. Maximum 26.14% reduction in Distortion Coefficient was verified.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.10a
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• pp.80-82
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• 2013

해상 물동량의 증가에 따라 선박들이 점차 대형화 되어 가고 있고 선박의 수 또한 지속적으로 늘어나고 있다. 이러한 현상은 곧 해양사고의 증가로 이어지고 있는데 이 중 인적과실에 의한 해양사고가 대부분의 원인으로 밝혀져 있다. 인적과실 중 항해나 당직근무 중 졸음에 의한 사고가 빈번한데 이를 방지하기 위하여 IMO(international maritime organization, 국제해사기구)에서는 선교 항해당직 경보시스템의 의무탑재를 시행하고 있다. 하지만 현행의 선교 항해당직 경보시스템은 재설정 방식에 따른 불편함 때문에 항해사들의 불만이 제기되고 있어 이에 대한 해소책으로 IMO에서는 모션센서를 선교 항해당직 경보시스템에 도입할 것을 권고하고 있다. 그러나 이 모션센서의 탐지기술이나 동작원리는 처음 육상용 화재경보시스템 혹은 보안시스템용으로 개발 및 제작되어진 것이므로 이를 특수한 조건인 선박의 항해당직에 적용할 때 야기될 수 있는 문제점이나 고려사항등을 검토해 볼 필요가 있다. 이 논문에서는 이 모션센서의 선교에서의 이상적인 구성, 필요한 기능, 적확한 작동여부, 모션센서와 압력센서나 음성인식센서와 같은 다른 수단과의 병용 등을 고려하여 모션센서의 최적기능 확보를 위한 성능기준을 제시하고자 한다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.55-59
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• 1992

최근 신 연삭 공구인 미세한 지립의 다이아몬드 휠을 이용함으로써 고경도와 취성을 지니는 엔지 니어링 세라믹스등의 신소재및 초경재 등 난삭재류를 대상으로 경면 가공을 추구하고자 노력이 진행중이다. 이는 래핑이나 폴리싱 등의 유리 지립에 의한 경면 창성법에 비하여 가공 능률이나 가공 정도가 높고 곡면이나 홈 등의 복잡 형상부의가공에도적용할 수 있다는 잇점이 있기 때문이다. 따라서 현재 이러한 신 연삭 가공법은 지금까지 연삭 가공후에 연마 가공 공정을 부가함으로써 초정 밀 효과를 지닐 수 있었던 각종 부품들에대한 단일 최종 마무리가공 공정으로의 응용에많은 기대를 걸고 있다. 본 연구는 높은 압축 강도치, 고온경도치와 내마모성, 강성 등을 지님으로써 외부 압력에 대한 변형률이 극히 적어 금형 칫수에가까운 제품을 생산할 수 있다는 특성으로 근래그 사용도가 급증 하고 있는 초경합금 금형재를 대상으로 해그 동안 난삭재에 대한 최적 가공 조건 설정이 정립되어 있지 못했던 관계로 인하여 기존의 숙련자 경험에만 주로 의존 할 수 밖에 없었던 단순한 다이아몬드 연삭 공구의 활용추세로부터 탈피하고 Diamond wheel 및 범용 연삭 공구를 최적으로 활용함으로써 연삭 가공의 초정밀화를 달성하며후 가공을 생략할 수 있는 가공 공정을 창출 해내기위하여, 상관 관계를 연삭 저항 및 가공 표면 품위등의 측면으로분석, 평가해봄으로써 초정밀 가공 차원에서의 최적 가공 조건 설정을 위한 지침을 명확하게 규명하기 위하여 실험적으로 수행하게 된 것이다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.14-17
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• 2010

To identify the turbulent flow characteristics resulted from the swirl direction of a combustor with seven swirl injectors, a 3D Large Eddy Simulation(LES) was implemented. The combustor of concern is the LRE combustor, designed by Aerospace Combustion Laboratory of Georgia Institute of Technology. The seven-clockwise-swirl-injectors combustor produces stronger flow interference among injectors, specially obvious tangential velocity near the wall, than the combustor with four-clockwise and three-counterclockwise swirl injectors. In addition, pressure fluctuations in the combustor with seven-clockwise-swirl-injectors was more amplified.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.51-57
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• 2021

The seawater cooling system of naval ships is installed to remove the toxic substances generated by CBR (Chemical, Biological, and Radiological) warfare and reduce the infrared signature of naval ships from outside the hull. The dispersion range of the nozzle is determined according to the injection pressure of seawater and the nozzle type. Therefore, it is necessary to select the appropriate injection pressure and design the optimal nozzles to increase the seawater dispersion area and maximize the efficiency of the cooling system. In this study, the applying feasibility of 3D printing technology to produce an injection nozzle for the seawater cooling system was examined. To this end, the extruded plastic specimens were fabricated by 3D printing, and the physical properties of the specimens were estimated through tensile testing. After this, the strain and stress of the nozzle as a function of the pressure were simulated by applying the estimated results to the finite element analysis. The finite element analysis results showed that the nozzle remained within the elastic range at the optimal pressure. The nozzle was estimated to be structurally stable, and the possibility of this study was confirmed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.5
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• pp.403-410
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• 2021

There are positive effects, such as pain reduction, when rheumatism patients exercise in water, but the cause of the pain reduction is unclear, and research on this is inadequate. This study examined the flow of the surface of the foot and the principles of pain relief. Unsteady simulations were conducted to analyze the flow, which was performed by repeatedly setting the movement of the foot raising and descending three times. Pressure fluctuations and frequencies were analyzed by designating pressure points at the painful location. The results showed that a positive and negative pressure of approximately ±500Pa was applied overall. A pressure of approximately ±2000Pa was applied when the direction of movement was changed. A frequency of approximately 35 to 80Hz was generated in the area where rheumatoid arthritis pain frequently occurs. The effects of reducing pain could be predicted when continuous pressure fluctuations and frequencies are applied repeatedly to the painful location, blood circulation promotion. The results could be used as basic data to understand the principles of aquatic exercise and support the development of underwater exercise programs and developing related medical equipment.

• Journal of Korea Entertainment Industry Association
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• v.13 no.1
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• pp.207-215
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• 2019

This study examines the effect of the height of cane that hemiplegic patients due to stroke use on their plantar pressure in standing position, gait speed. The study suggests a new standard for appropriate cane height that considers the change of average height of population. Research subjects included 12 patients hospitalized in S Medical Care Hospital located in Gwangju Metropolitan City in South Korea who were diagnosed with stroke. Group A uses a cane of the height of the greater trochanter of femur, group B uses a cane of 5cm above the height of the greater trochanter of femur, and group C is a cane of 10cm above the height of the greater trochanter of femur. In the study result, non-affected side plantar pressure and affected side plantar pressure showed a significant difference among the cases where the cane height was the same as the A group, B group, C group. In the post-hoc analysis result, a significant difference was observed between the case of A group and C group. Gait speed showed no significant difference among the case of the A group, B group, C group. The asymmetry of the stroke affects not only the posture but also the walking that is related to daily life. Changes in the height of the cane did not affect walking speed. The change in the height of the cane showed a change in the weight support ratio, which is thought to have a positive effect on the asymmetry. In future clinical setting, this study result will be able to provide fundamental data regarding the cane height in the standing or walking therapy for hemiplegic patients due to stroke with cane application.