• 한국전산유체공학회지
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• 제15권2호
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• pp.7-13
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• 2010

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 5.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}10^6$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental datum in the low aspect ratio cavity (L/D = ~4.5). In the high aspect ratio cavity, however, there are other low dominant frequencies of the leading edge shear layer with the dominant frequencies of the feedback mechanism.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.311-314
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• 2006

The supersonic flow around tandem cavities was investigated by three- dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes(RANS) equation with the $\kappa-\omega$ thrbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split using van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge-Kutta method. The aspect ratio of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two-dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the fire cavity flow cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• 대한한방내과학회지
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• 제35권3호
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• pp.274-287
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• 2014

Objectives: This study was aimed to figure out an agreement between the diagnosis of nasal endoscopy and a preexisting questionnaire focusing on Cold-Heat pattern. Methods: 52 patients with cough who met the criteria filled out a pattern questionnaire and the examiner looked at their nasal cavities through nasal endoscopy. According to the checked questionnaire results, the subjects were identified by 6 patterns. After examining subject's mucous membrane of oropharynx and nasal cavity through nasal endoscopy, we classified each to the Cold or Heat group. Correlation between questionnaire and nasal endoscopy results was analyzed. Results: In diagnosing Cold-Heat, there was no significant difference by McNemar test (p=0.227) between nasal endoscopy and the questionnaire, and the two methods agreed moderately (${\kappa}=0.428$). The color of mucous membrane of oropharynx and the Cold-Heat pattern on questionnaire agreed slightly (${\kappa}=0.133$). The color of mucous membrane of nasal cavity and the Cold-Heat pattern on questionnaire agreed fairly (${\kappa}=0.384$). In the patients with cough related to upper respiratory tract, they got higher diagnosis accuracy than the patients with cough related to lower respiratory tract did. Similarly, external cough patients got higher diagnosis accuracy than internal cough patients did. Conclusions: To identify Cold or Heat, examining oropharynx and nasal cavity using nasal endoscopy is a meaningful method in patients with cough, showing that two diagnosis methods which use nasal endoscopy and questionnaire agreed moderately. Especially, it is more useful diagnosing patients with cough related to the upper respiratory tract than diagnosing the patients with cough related to the lower respiratory tract.

• 대한한방내과학회지
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• 제36권3호
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• pp.323-334
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• 2015

Objectives This study was designed to analyze the characteristics of craniofacial hyperhidrosis and palmar/plantar hyperhidrosis by nasal endoscopy and body composition test. Methods The study sample consisted of 20 and 22 patients with craniofacial hyperhidrosis and palmar/plantar hyperhidrosis, respectively, who answered questionnaires and underwent nasal endoscopy and body composition test. The questionnaires estimated the quality of life by Dermatology Life Quality Index score (DLQI), and the degree of obesity was evaluated using body mass index (BMI), percent body fat (PBF), and waist-hip ratio (WHR). The state of nasal cavity was evaluated by color, humidity, and swelling of the mucous membranes, and runny nose. Results BMI, PBF, and WHR were higher in patients with craniofacial hyperhidrosis than in patients with palmar/plantar hyperhidrosis. Rhinitis score was not significantly different between craniofacial hyperhidrosis and palmar/plantar hyperhidrosis. There was a positive correlation between rhinitis score and DLQI. Conclusions The degree of obesity was higher in patients with craniofacial hyperhidrosis than in those with palmar/plantar hyperhidrosis. The state of nasal cavity was not significantly different between craniofacial hyperhidrosis and palmar/plantar hyperhidrosis, but was associated with quality of life of hyperhidrosis patients.

• Journal of Ecology and Environment
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• 제29권2호
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• pp.75-84
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• 2006

In Korea, a bibosoop is a type of village grove fostered to complement a weak part of the village from a Feng-Shui perspective. We examined the characteristics of bird communities in remaining bibosoops in two regions, Gyeonggi-do Province and Jeollanam-do Province. We surveyed patch preferences of birds at two landscapes in Gyeonggi-do Province. One contains a bibosoop with other rural landscape elements, and the other does not have a bibosoop. The two landscapes of Gyeonggi-do Province were similar to each other in the distribution of landscape elements. We observed that species richness was significantly higher at the site with a bibosoop, and that tits, Mandarian ducks, starlings, Eurasian scops owls, and woodpeckers utilized the bibosoop as a nesting site. Birds preferred the landscape with the bibosoop, and the internal movement of birds was significantly higher at the landscape with the bibosoop than at the other. The results suggest that bibosoops serve as a unique biotope that provides nest sites for cavity nesters, especially near nest-insufficient forests, and enhance the internal movements of birds among patches in the landscape.

• Tuberculosis and Respiratory Diseases
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• 제48권5호
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• pp.709-719
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• 2000

연구배경 : 폐결핵의의 활동성 여부를 판정하는 방법으로 객담검사에 더불어 HRCT가 유용한 것으로 알려져 있다. 이에 저자들은 객담 도말 및 배양검사의 결과와 HRCT 소견을 비교하고자 하였다. 방법 : 1996년 3월부터 1998년 9월까지 을지대학병원 호흡기내과에 내원한 활동성 폐결핵 환자를 대장으로 객담도말 및 배양검사와 HRCT를 시행하여 객담검사 결과에 따라 1군(도말(-)배양(-)군), 2군(도말(-)배양(+)군), 3군(도말(+),배양(+)군)으로 분류 하였고, 각 군에서의 HRCT소견을 비교하는 전향적 연구를 시행하였다. 결과 : 도말(+),배양(+)인 3군에서는 acinar nodule, macronodule, cavity가 각각 100%. 75%, 75%로서 도말(-)배양(-)인 1군(63%, 18%, 9%)과 도말(-)배양(+)인 2군(46%, 15%, 23%) 보다 통계적으로 유의하게 많이 관찰되었다(p<0.05). centrilobular nodule and branching structure는 3군(92%)이 1군(54%) 보다 유의하게 많았으나(p<0.05), 2군(77%)과는 통계적으로 차이가 없었다. 객담 항상균 도말 양성군은 음성군에 비해 acinar nodule(100% vs 54%), macronodule(75% vs 17%), cavity(75% vs 17%)가 통계적으로 유의하게 많이 관찰되었다(p<0.05). 결핵균 배양 양성군은 음성군에 비해서 acinar nodule(72% vs 45%), cavity(48% vs 9%)가 통계적으로 유의하게 많이 관찰되었다(p<0.05). 결론 : 임상증상과 흉부 X-선으로 활동성 폐결핵이 의심되는 환자에서 HRCT는 활동성 판정에 도움이 되며, centrilobular nodule and branching structure, acinar nodule, macronodule, cavity등의 소견은 객담 도말 검사상 음성이라도 항결핵제 투여와 함께 균 동정을 위한 유도객담 및 기관지경 검사의 필요 여부를 결정하는데 도움이 될 것으로 생각된다.

• Journal of Biosystems Engineering
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• 제27권1호
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• pp.59-66
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• 2002

The objectives of the study were to analyze the acoustic characteristics related to the internal quality factors of watermelon(Citrulus Vulgaris Schrad). Among the various internal quality factors, only four factors such as ripeness, inside cavity, yellow belt and blood flesh were considered in this study. Relationships between the internal quality factors, the day after fruit set and the day after harvest were also investigated. Test apparatus was the same as the apparatus described in the previous study(Choi et at., 2000). The selected sample was divided into four groups; 69 samples used for ripeness tests 56 samples for ripeness test along the day after fruit set and for yellow belt detection, 60 samples for ripeness along the day after harvest 44 samples fur blood flesh detection. It was shown that the first peak frequencies shifted to the lower range and the energy ratios of the bandwidths between 0∼550 Hz to the bandwidths between 850∼2500 Hz increased as the day after fruit set elapsed. Since the acoustic responses of the watermelon such as frequency and magnitude began to change from 10 days after harvest, the storage period of watermelon in a normal temperature condition seemed to be approximately 10 days after harvest. The ratios of the first peak amplitude to the maximum peak amplitude fur the sound watermelon showed the higher value than that fur watermelon with cavity inside, and the separation between the sound and cavity inside could be accomplished by the ratio value of 0.25. The energy ratios (0∼550 Hz/850∼2,500 Hz) for the watermelon with cavity inside showed the higher value than 2.3. The frequency characteristics of the yellow belt watermelon appeared mostly in the range of 600∼900 Hz frequencies. The yellow belt watermelon showing the energy spectral density function at this frequency range to be over 70 seemed to be not a marketable commodity, The energy ratios(0∼550 Hz/850∼2,500 Hz) for the blood flesh watermelon showed the higher value than 3.5.

• Journal of Mechanical Science and Technology
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• 제20권8호
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• pp.1256-1265
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• 2006

The supersonic flows around tandem cavities were investigated by two-dimensional and three-dimensional numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) equation with the k- ω turbulence model. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves, and the acoustic effect transmitted from wake flow to upstream. The upwind TVD scheme based on the flux vector split with van Leer's limiter was used as the numerical method. Numerical calculations were performed by the parallel processing with time discretizations carried out by the 4th-order Runge- Kutta method. The aspect ratios of cavities are 3 for the first cavity and 1 for the second cavity. The ratio of cavity interval to depth is 1. The ratio of cavity width to depth is 1 in the case of three dimensional flow. The Mach number and the Reynolds number were 1.5 and $4.5{\times}10^5$, respectively. The characteristics of the dominant frequency between two- dimensional and three-dimensional flows were compared, and the characteristics of the second cavity flow due to the first cavity flow was analyzed. Both two dimensional and three dimensional flow oscillations were in the 'shear layer mode', which is based on the feedback mechanism of Rossiter's formula. However, three dimensional flow was much less turbulent than two dimensional flow, depending on whether it could inflow and outflow laterally. The dominant frequencies of the two dimensional flow and three dimensional flows coincided with Rossiter's 2nd mode frequency. The another dominant frequency of the three dimensional flow corresponded to Rossiter's 1st mode frequency.

• 한국추진공학회지
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• 제25권2호
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• pp.1-11
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• 2021

연소기 내부의 공동은 낮은 속도의 재순환영역과 유동의 진동을 일으켜 연료와 공기의 혼합 효율을 증대시키고, 화염을 유지함으로써 지속적인 연소를 가능하게 한다. 본 연구에서는 공동의 형상 인자에 따른 내부 유동의 특성을 실험과 2차원 전산해석을 통해 관찰하였다. 초음속 연소기 내 유동은 단순히 L/D 이외에도 다양한 공동 형상인자에 따라 크게 영향을 받는 것이 관찰되었다. 동일 L/D에서도 공동의 깊이에 따라 open과 closed 형태가 나타남을 확인하였고, 공동의 후방 경사각, 연소기 높이도 유동 특성이 달라지며, 이는 전압력 손실에 큰 영향을 미치는 것을 확인하였다.