• 설비공학논문집
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• 제17권8호
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• pp.754-763
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• 2005

This paper introduces a new concept compressor in which piston orbits in the cylinder having an annular space formed between two concentric circular walls. In this configuration, two gas pockets are formed with $180^{\circ}$ phase difference: one between the wrap of the orbiting piston and the inner cylinder wall and the other between the piston wrap and the outer cylinder wall. This alternating feature of gas compression and discharge processes yields several advantages such as low torque variation and low gas pulsation. Computer simulation program has been developed to evaluate the compressor performance. The volumetric, adiabatic, and mechanical efficiencies of the orbiter compressor are calculated to be $85.6\%,\;97.2\%,\;and\;95.2\%$, respectively, when it is used as an air compressor.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
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• pp.41-43
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• 2013

In order to simulate and visually observe combustion phenomena in cylindrical radial-flow porous inert media, a radial multi-channel burner, made of transparent quartz plates, was fabricated. Flame stabilization characteristics and its pulsating instability in the burner were experimentally investigated with respect to various mixture flow rates and equivalence ratio. As a result, five different flame behaviors, such as stable flame, pulsating instability, sudden extinction, blowout and unstable extinction, were observed. Mean radial position of circularly arranged multi-flame and its averaged burning velocity were measured and then compared to the freely propagating flame. The multi-flame pulsation frequency is about several tens of Hz and it is supposed to be generated by the heat diffusion enhancement to cold pre-mixture by the intensive gas-solid interaction.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.102-115
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• 2020

In this study, the SST k - ω turbulence model and the sliding mesh technology based on RANS method have been adopted to simulate the exciting force and hydrodynamic of a pump-jet propulsor in different oblique inflow angle (0°, 10°, 20°, 30°) and different advance ratio (J = 0.95, J = 1.18, J = 1.58).The fully structured grid and full channel model have been adopted to improved computational accuracy. The classical skewed marine propeller E779A with different advance ratio was carried out to verify the accuracy of the numerical simulation method. The grid independence was verified. The time-domain data of pump-jet propulsor exciting force including bearing force and fluctuating pressure in different working conditions was monitored, and then which was converted to frequency domain data by fast Fourier transform (FFT). The variation laws of bearing force and fluctuating pressure in different advance ratio and different oblique flow angle has been presented. The influence of the peak of pulsation pressure in different oblique flow angle and different advance ratio has been presented. The results show that the exciting force increases with the increase of the advance ratio, the closer which is to the rotor domain and the closer to the blades tip, the greater the variation of the pulsating pressure. At the same time, the exciting force decrease with the oblique flow angle increases. And the vertical and transverse forces will change more obviously, which is the main cause of the exciting force. In addition, the pressure distribution and the velocity distribution of rotor blades tip in different oblique flow angles has been investigated.

• 한국해양공학회지
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• 제27권3호
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• pp.73-78
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• 2013

CFD (computational fluid dynamics) analyses that considered the dynamic interaction effects between the flow and a turbine were performed to evaluate the power output characteristics of two representative vertical-axis tidal-current turbines: an H-type Darrieus turbine and Gorlov helical turbine (GHT). For this purpose, a commercial CFD code, Star-CCM+, was utilized, and the power output characteristic were investigated in relation to the scale ratio using the relation between the Reynolds number and the lift-to-drag ratio. It was found that the power coefficients were significantly reduced when the scaled model turbine was used, especially when the Reynolds number was lower than $10^5$. The power output characteristics of GHT in relation to the twisting angle were also investigated using a three-dimensional CFD analysis, and it was found that the power coefficient was maximized for the case of a Darrieus turbine, i.e., a twisting angle of $0^{\circ}$, and the torque pulsation ratio was minimized when the blade covered $360^{\circ}$ for the case of a turbine with a twisting angle of $120^{\circ}$.

• Journal of Astronomy and Space Sciences
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• 제37권1호
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• pp.19-27
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• 2020

Pc1 pulsations are important to consider for the interpretation of wave-particle interactions in the Earth's magnetosphere. In fact, the wave properties of these pulsations change dynamically when they propagate from the source region in the space to the ground. A detailed study of the wave features can help understanding their time evolution mechanisms. In this study, we statistically analyzed Pc1 pulsations observed by a Bohyunsan (BOH) magneto-impedance (MI) sensor located in Korea (L = 1.3) for ~one solar cycle (November 2009-August 2018). In particular, we investigated the temporal occurrence ratio of Pc1 pulsations (considering seasonal, diurnal, and annual variations in the solar cycle), their wave properties (e.g., duration, peak frequency, and bandwidth), and their relationship with geomagnetic activities by considering the Kp and Dst indices in correspondence of the Pc1 pulsation events. We found that the Pc1 waves frequently occurred in March in the dawn (1-3 magnetic local time (MLT)) sector, during the declining phase of the solar cycle. They generally continued for 2-5 minutes, reaching a peak frequency of ~0.9 Hz. Finally, most of the pulsations have strong dependence on the geomagnetic storm and observed during the early recovery phase of the geomagnetic storm.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.453-458
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• 2000

The paper describes a study of the variation of the NO production emitted from turbulent propane flames established on a practical combustor where a primary and a secondary fuel lines are installed. The flowrate of the secondary fuel is pulsated or added in addition to that of the primary fuel which constrantly flows to the nozzle of the burner. Two modes depending on the positions of supplying the secondary fuel are performed; one is for its position to be placed at the center of the primary fuel tube and the other around the stabilization baffle. The mean concentrations of gas species, $O_2,\;Co\;CO_2,\;NO$, and HC(unburnt hydrocarbones) have been measured at the exit of the combustor. As equivalence ration $({\Phi})$ is increased the profile of the NO concentration on the latter mode rises slowly less than that on the former one. In the range of ${\Phi}=0.5$ to 0.54 the NO production is reduced by about 35% more on the latter mode than on the former one. The influence of pulsating the secondary fuel on the variation of the NO concentration doesn't appear at both modes.

• 한국항공우주학회지
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• 제32권8호
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• pp.29-36
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• 2004

초음속 흡입구 buzz는 입구에서의 충격파 패턴의 진동과 내부압력요동을 동반하는 불안정한 아임계 작동으로 정의할 수 있다. 이러한 유동섭동은 연소실 실화나 엔진의 구조직 손상을 일으킬 수 있다. 축대칭, 외부 압축형 흡입구에서 초음속 흡입구의 buzz 현상을 조사하기 위한 실험적 연구가 수행되었다. 자유류 마하수 2.0에서 카울 입구 직경이 30mm인 흡입구 모델이 시험되었다. 아임계 불안정성은 압력섭동의 주파수 및 입구에서의 충격파 구조 분석을 통해 조사되었다. 실험결과 전압럭 회복비는 0.42에서 0.78까지, 포획 면적 비는 0.34에서 0.98까지 변화했다. 아임계 유동의 주파수는 포획 면적비 감소에 따라 증가했으며 주파수는 범위는 $224{\sim}240Hz$였다.

• 한국전자통신학회논문지
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• 제14권6호
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• pp.1257-1264
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• 2019

기존의 Cuff 기반의 혈압(Blood Pressure)측정 방법은 연속적인 실시간 혈압측정에는 한계를 갖는다. 이러한 이유로 ECG와 PPG 센서 신호를 상호융합한 다양한 혈압추정이 이루어졌다. 그러나 PPG 중심에 측정기법은 AC 노이즈, 작은 맥동, 비박동 등의 많은 문제를 지니고 있다. 본 논문은 ECG와 PPG 관계에 발생하는 맥파전달시간(PTT)과 맥파속도(PWV)를 이용하여 혈압을 추론기법이다. 신호 피크를 이용하는 HRF(Height Ratio Features)에 비해, 본 제안방식은 ECG, PPG의 최고점 혹은 최저점을 사용한 시차를 이용해 추정하기 때문에 PPG 센싱 시그널의 오류에도 안정적인 추출이 가능한 장점이 있다. 본 논문에서 제안 방법을 이용하여 25만 회의 혈압측정의 결과 ±28.5%의 정확도를 갖는 혈압 추정기법을 제시할 수 있었다.

• 한국진공학회지
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• 제5권4호
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• pp.377-386
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• 1996

오스테나이트 스테인리스강 304L을 고질소 저압 분위기에서 400~$600^{\circ}C$ 범위내의 온도변수 $50^{\circ}$간격차이에 따라 펄스 직류 플라즈마를 발생시켜 펄스작용 시간비에 따라 5시간씩 질화처리를 실시하였다. 처리온도 $500^{\circ}C$를 전후하여 질화처리층의 상과 조직이 현저히 다르게 형성되었다. $500^{\circ}C$미만 범위에서 저온일수록 펄스작용 시간비가 높을 때 질화층은 일종의 비화학량론적인 질화 스테인리스강으로 형성되었고 박피막을 이루며 균열이 많이 발생했다. 처리온도가 $500^{\circ}C$보다 높을 때는 온도가 높아지거나 펄스작용 시간비가 50s/100s로 높아짐에 따라 질화층은 CrN 및 Fe4N 위주로 구성되어 주상정 조직을 이루며 균일하게 성장하며 무균열층이 된다. $500^{\circ}C$에서는 저온 조직 및 상과 고온 조직 및 상이 혼합된 질화층이 형성되며 취성이 대단히 크다.

• 대한간호학회지
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• 제14권2호
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• pp.93-111
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• 1984

The main purpose of this study is to develop a ratio scale measuring level of pain using Korean pain terms. The specific purposes of this study are to identify the degree of pain of each pain term in each subclass: to classify each subclass in terms of dimensions of pain; and to analyze factors of the Korean pain ratio scale clustering together. One hundred an4 fifty eight pain terms which were originally identified as representative terms and their synonyms were used for data collection. Fifty eight nursing professors ana sixty one medical doctors who have contacted with patients having pain were asked to rate the weight of each pain term on a visual analogue scale. Subclasses in which ranks of pain terms were same f s findings in two previous studies were 1) thermal 3 am 2) cavity pressure, 3) single stimulating pain, 4) radiation pain. and 5) chemical pain. Subclasses in which ranks of pain terms were confused were 1) incisive pressure, and 2) cold pain. Subclasses in which one new pain term was added were 1) inflammatory-repeated pain, 2) punctuate pressure, 3) constrictive pressure, 4) fatigue-related pressure, and 5) suffering-relate4 pain. Subclasses in which two new pain terms were added were 1) traction pressure, 2) peripheral nerve pain, 3) dull pain, 4) pulsation-related pain, 5) digestion-related pain, 6) tract pain, and 7) punishment-related pain. Subclass in which 3 new pain terms were included was fear-related pain. Rating scores of 5 words in 4 subclasses were significantly different between the normal group and the extreme group of subjects in terms of subjective rating. Only one word among 6 words was that newly added to the scale. Rating scores of 12 words in 9 subclasses were significantly different between doctor group and nursing professor group. Among these 12 words, only 3 were those newly added to the scale. In comparison of these 12 words, mean scores of the nursing professors were always 7 to 16 points higher than those of the medical doctors. In the analysis of judgement of subjects in terms of dimensions of pain terms, subclasses of dull pain, cavity pressure, tract pain and cold pain were suggested to be included in the miscellaneous dimension. As a result of factor analysis of the ratings given to 96 pain words using principal components analysis without iteration and with varimax rotation limiting the number of factors to 4, factors of severe pain (factor I) mild-moderate pain (factor II) , causative pain (factor III) and temperature-related pain(factor IV) were extracted with the factor loading above 0.388. When the pain words were re-arranged on the bases of factor loading above 0.368, number of factors decreased to only first two factors. Maximum score of pain word in factor II was 46.17 and the minimum score of the factor I was 45.36. Further studies are needed to identify the validity, reliability, sensitivity and practicability of this ratio scale using patients having various sources of pain.