• International Journal of Naval Architecture and Ocean Engineering
• /
• 제12권1호
• /
• pp.799-809
• /
• 2020

In this study, the supercavitating flow of a high-velocity moving body near air-water surface is calculated and analyzed based on a commercial CFD software ANSYS Fluent. The effect of regular wave parameters including both wave height and wavelength on the cavitating flow and force characteristics of a body at different velocities is investigated. It is found that the cavity shape, lift coefficient and drag coefficient of the body vary periodically with wave fluctuation, and the variation period is basically consistent with wave period. When the wavelength is much greater than the cavity length, the effect of wave on supercavitation is the alternating effect of axial compression and radial compression. However, when the wavelength varies around the cavity length, the cavity often crosses two adjacent troughs and is compressed periodically by the two wave troughs. With the variation of wavelength, the average area of cavity shows a different trend with the change of wave height.

• 대한방사선치료학회지
• /
• 제26권1호
• /
• pp.107-114
• /
• 2014

목 적 : 두경부 치료계획 CT영상에서 dental implant로 인한 metal artifact 발생 시 O-MAR(Metal artifact Reduction for Orthopedic Implants)(ver. 3.6.0, Philips, Netherlands)를 적용할 수 있을지 여부를 평가하고자 한다. 대상 및 방법 : 모든 CT영상은 Brilliance Big Bore CT(Philips, Netherlands)에서 관전압 120kVp, 2mm 두께로 촬영하였으며, O-MAR를 이용하여 Metal artifact reduction 후 전산화치료계획장비(Eclipse ver 10.0.42, Varian, USA)로 원본영상과 비교, 분석하였다. O-MAR의 기본적인 성능 테스트를 위해 Metal artifact가 발생하지 않은 영상과 발생한 영상에서 O-MAR 적용시, HU 변화를 검증하기 위해 원통형 팬텀과 cerrobend 막대, 불균질 팬텀을 이용하여 실험하였다. 각각의 원본 영상과 O-MAR 적용 영상에서 관심영역 내 HU 변화를 측정하였다. 이를 바탕으로 본 연구의 주목적인 dental implant로 인한 metal artifact 발생 영상을 재현하기 위해 팬텀을 제작하여 사용하였고, 실제 임상 환자 영상에 O-MAR를 적용한 영상과 원본 영상 그리고 artifact 부분을 보정한 영상의 선량 분포를 SNC Patient(Sun Nuclear Co., USA)로 비교하였다. 결 과 : 두경부에서의 metal artifact를 재현한 원본 영상과 O-MAR 적용영상의 선량 분포를 비교한 결과 gamma passing rate 는 2 mm / 2% 기준으로 99.8%, 일치를 보였다. 실제 임상 환자 영상을 바탕으로 O-MAR 적용 전후 영상과 density corrected CT 영상에 동일한 조건으로 치료 계획을 수립하여 선량 분포를 비교한 결과는 98.5% 일치로 비교적 높은 gamma passing rate를 보였다. 전체적인 선량 분포 차이는 모두 2% 이내로 팬텀 실험과 실제 임상 환자 영상 실험에서 비슷한 결과로 나타났다. 하지만 선량 편차가 적더라도 국소적으로 집중되어 있는 것은 문제의 소지가 될 가능성이 있다. 화질 개선 면에서는 모든 실험에서 O-MAR 적용영상이 원본에 비해 개선됨을 알 수 있었으나, 두경부 metal artifact를 재현한 팬텀 영상 air cavity 내에서 최대 HU 값이 상승하는 경우가 생겼고, 환자 영상에서는 air cavity가 tissue로 잘못 보정되는 경우 또한 발견할 수 있었다. 결 론 : 업체에서 제시한 사용제한 사항인 피부 근처와 저밀도 영역이 공존하는 두경부에서 O-MAR의 사용 가능성을 확인해 본 결과, 원본의 왜곡과 보정이 동시에 일어났다. 심지어 팬텀 실험보다 더 심한 artifact가 생긴 환자의 경우 air cavity가 tissue로 잘못 보정되는 경우도 발생하였다. 결과적으로 아직까지는 O-MAR 알고리즘이 air cavity와 photon starvation artifact를 정확히 구분하지 못하는 것으로 보인다. 선량 측면에서의 영향은 임상에서 배제될 만큼 큰 차이를 보이지는 않았다. 임상에서 원본과 O-MAR 적용 영상을 비교하며 작업한다면 contouring, artifact 보정작업, DRR 화질 개선 등에 도움을 받을 수 있을 것으로 사료된다.

• 대한간호학회지
• /
• 제9권2호
• /
• pp.17-26
• /
• 1979

This research is to prevent the infection of maternity in the hospital by examining the microbes contaminations in maternity through airbone microbes and those who are engaged in the ward of O.B. ＆ G.Y. and to furnish the basic data available to hospital management. The bacterial growth of airbone microbes contaminations in nosocomial air and who thor the nasal cavity of passers by (doctors, nurses, parturient women) who went to the ward of O.B. ＆ G.Y. contaminated or not were examined in“E”Univ. Hospital from July to August, 1979 by using thioglycollate broths and agar plates. The following results were obtained: 1. The average colony number of airborne microbes revealed as follows the pediatric ward (36 colonies), the internal ward (33 colonies), the ward of O.B. ＆ G.Y. (30 colonies), the ward of surgery (24 colonies), delivery-waiting room (11 colonies), and the delivery room (3 colonies). 2. The bacterial growth beforenoon differed from that of afternoon. Namely, the latter (24 colonies) was higher than the former (21 colonies). 3. The type of strains isolated from the air of the ward revealed staphylococci (82%), Gram negative bacilli (18%), fungi (17%), Gram positive diplococci (13%), and Bacillus subtilis (2.8%). 4. The strains isolated in the delivery-waiting room revealed staphylococci (66.7%), Gram negative bacilli (33.6%), and revealed staphylococci (75%), Gram positive diplococci (8.3%), and fungi (8.3%), in delivery room. 5. Most of strains isolated in the ward of O.B. & G.Y. revealed staphylococci (100.0%), Gram positive diplococci (8.3%), and Gram negative bacilli (6.7%). 6. The strain isolated in the surgical ward revealed staphylococci (91.7%), fungi (33.3%), Gram positive diplococci (25%), Gram negative bacilli (25%) and Bacillus subtilis (8.3%). 7. The strain isolated in the pediatric ward revealed staphylococci (75%), fungi (25%), Gram positive diplococci (8.3%), Bacillus subtilis (8.3%), and Gram negative bacilli (8.3%). 8. The strain isolated in the internal ward revealed staphylococci (91.7%), fungi (33.3%), Gram positive diplococci (25%), and negative bacilli (16.7%). The strains isolated from the nasal cavity of those doctors and nurses who and enaged in the ward of O.B. & G.Y. revealed staphylococci (80%), Bacillus subtilis (10%), and Gram negative bacilli (10%), from doctors and Gram positive diplococci (10%), instead of Gram negative bacilli (10％), from nurses. 10. The strain isolated from nasal cavity of parturient women on admission revealed staphylococci (90%), and Gram negative bacilli (10%), but after admission revealed staphylococci (70％), Gram positive diplococci (10%), and Gram negative bacilli (10%). 11. Of the total 91 staphylococci isolated from the air of the ward, the Coagulase pastive was 36 (39.6%), and the negative 55 (60.4%), As a result of the coagulase experiment of the staphylococci isolated from the nasal cavity of those who are engaged in the ward of O.B. ＆ G.Y. all were revealed as negative that belonged to non-pathogenic. 12. Consequence of the biochemic examination of the gram negative bacilli isolated from the air of the ward the aerobacter aerogens revealed was (16.7%) E-coli 5％ in the nasal cavity of those came and went to the of O.B. ＆ G.Y. and Aerobacter aerogens 7.5%.

• 제어로봇시스템학회논문지
• /
• 제20권2호
• /
• pp.107-111
• /
• 2014

An SIW cavity is a useful tool to design an FSS which shows a rapid roll-off rate and insensitivity to polarizations and incident angles of electromagnetic waves. However, due to its high Q-factor, the FSS also shows narrow bandwidth which is undesirable for high-capacity communication. To address this drawback, we propose a novel technique to enhance the bandwidth while maintaining similar frequency response characteristics and minimizing the increase of the overall thickness of the SIW cavity FSS. In order to verify the performance of the technique, simulated frequency responses will be provided. Also, a parameter which affects the bandwidth will be studied. Finally the stability to polarizations and incident angles will be observed through the simulated results.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
• /
• pp.91-91
• /
• 2011

This paper describes development procedure of the four types of fuel cell's blowers: pressurized fuel blower, selective oxidation air blower, cathode air blower, and burner air blower. Diaphragm blowers having two heads are selected to maintain force balance when the rotating arms are moving by the driving motor. Dimensions of a diaphragm cavity is designed according to the optimal design procedure using numerical simulation and experimental measurement. Experimental apparatus is designed by considering the bower characteristics having low flow rate and high pressure. Test blower is operated by a diaphragm, which has suction and discharge port on the top of the blower. For analyzing the internal flow of the blower, three-dimensional Navier-Stokes analysis is introduced in the present study. Throughout the optimal design of the blowers, blower performance is enhanced by reducing the unbalance motion of the rotating arm and loss region in the diaphragm cavity.

• 음성과학
• /
• 제9권4호
• /
• pp.3-14
• /
• 2002

VPI occurs when the velum and lateral and posterior pharyngeal wall fail to separate the nasal cavity from the oral cavity during deglutition and speech. There are a number of congenital and acquired conditions which result in VPI. Congenital conditions include cleft palate, submucous cleft palate and congenital palatal insufficiency (CPI). Acquired conditions include carcinoma of the palate or pharynx and neurologic disorders. The speech characteristics of VPI is characterized by hypernasality, nasal air emission, decreased intraoral air pressure, increased nasal air flow, decreased intelligibility. VPI can be treated with various methods that include speech therapy, surgical procedures to reduce the velopharyngeal gap, speech aid prosthesis, and combination of surgery and prosthesis. This article describes four cases of VPI treated by speech aid prosthesis and speech therapy with satisfactory result.

• 한국분무공학회지
• /
• 제1권2호
• /
• pp.16-23
• /
• 1996

In case of a high-speed D.I. diesel engine. the injected fuel spray is unavoidable that the impinging on the wall of piston cavity and in this case the geometry of piston cavity has a great influence on the atomization structure and air flow fields. In the field of combustion and in many other spray applications, there are clear evidence of correlation between spray structure and emission of pollutants. Ordinary, the combustion chamber of driving engine have unsteady turbulent flow be attendant on such as the change of temperature, velocity and pressure. So the analysis of spray behavior is difficult. In this study, a single spray was impinged on each cavity wall at indicated angle in a quiescent atmosphere at room temperature and pressure, as being the simplest case, and 3 types of piston cavity such as Dish, Toroidal and Re-entrant type was tested for analyzing the influence of cavity geometry. And hot wire probe was used for analyze non-steady flow characteristics of impinging spray, and to investigate the behavior of spray, the aspects of concentration c(t), standard deviation $\sigma(t)$ and variation factor (v.f.) was measured with the lapse of time.

• 한국소음진동공학회논문집
• /
• 제17권12호
• /
• pp.1223-1229
• /
• 2007

Flow traveling over a cavity opening forms a vortex due to unstable shear layer and induces an aerodynamic pressure excitation from the diffusion of the vortex convecting out of the trailing edge of the opening. The interaction between the excitation force and the cavity response sustains resonance in the resonator(cavity) and locked-in vortex shedding at the leading edge of the opening. The aerodynamic excitation force can be described from the diffusion of the vortex over the trailing edge and the level of its diffusivity is related to the strength of vorticity seeded at the leading edge. In this study, the control scheme of the internal pressure oscillation was proposed from regulating the vorticity at the leading edge by use of an oscillating spoiler. It was found that the relative motion between the spoiler and the air mass at the cavity opening influenced vorticity strength and the control was achieved by direct feedback of the cavity pressure fluctuation to the actuator.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
• /
• pp.359-363
• /
• 2005

스크램제트 엔진은 대기중의 공기를 흡입하여 연소실에서 초음속으로 연소하는 방식으로 짧은 시간 동안 연료와 공기가 혼합하고 연소되어야하는 특징이 있다. 연료와 공기 혼합을 증대하는 방법은 여러 가지가 제시되었다. 이중 자유류 마하수 2.5의 단일분사 방법에서의 cavity를 이용한 혼합증대 특성을 알아보기 위해 수치해석을 수행하였다. 수치해석은 상용코드인 CFD-Fastran의 3차원 Navier-Stokes 방정식과 Menter SST(Shear Stress Transport) 난류모델을 적용하였다. cavity 뒤쪽 0.5 cm 떨어진 곳에 지름 0.1cm의 Jet 분사구를 통해 수직분사를 시켜 cavity의 유무에 따른 혼합특성을 살펴보았고, cavity에 대한 영향을 알아보기 위해 $3\times2\times1\;cm$ 크기의 cavity를 사용했다. 계산된 결과는 동일조건의 실험으로 검증하였고 이를 통해 cavity에 의한 혼합증대 특성을 확인할 수 있었다.

• 콘크리트학회지
• /
• 제4권1호
• /
• pp.89-96
• /
• 1992

콘크리트의 내동해성은 일반적으로 공기량이나 기포조직 및 분포에 따라 크게 영향을 받으며 콘크리트의 강도와도 관련이 있는 것으로 알려져 있다. 본 연구에서는 고강도콘크리트의 동결융해 저항성에 미치는 공기량 및 기포조직 특히 간격계수의 영향에 관한 실험적 연구로서 우선 압축강도는 Non-AE콘크리트를 대상으로 400-500kg/$\textrm{cm}^2$를 목표로 하였고, 실험결과 내구성지수가 10~20%정도에 불과하므로 다음단계로 공기량 2~12%인 AE콘크리트로 하여 내구성 향상을 도모하였다. 이 때 단위시멘트량, 물\ulcorner시멘트비등을 변화시킨 20종류의 콘크리트 배합에 대해 500cycle까지 동결융해시험을 실시하였다. 결론적으로 동결융해의 저항성은 물\ulcorner시멘트비 보다는 공기량과 더 밀접한 관계가 있었고 임계내구성지수에 대응하는 간격계수는 물\ulcorner시멘트비에 따라 다르다는 사실을 알 수 있었다.