• 한국추진공학회지
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• 제12권5호
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• pp.9-17
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• 2008

액체추진제 추력기 인젝터로부터 발생하는 분무의 분열과 확산거동을 파악하기 위해 이중모드 위상 도플러속도계(DPDA)를 사용하여 분무액적의 준3차원적 공간분포를 계측하고 도시한다. 분무는 27.6 bar의 분사압력 조건에서 길이-직경비가 1.67인 노즐 오리피스로부터 지면에 수직으로 분사된다. 분무 액적의 수직 및 수평방향 평균속도, SMD, 그리고 체적유속은 분무의 상류/중심에서 하류/외곽으로 이동함에 따라 분무분열에 의해 그 크기가 감소한다. 분무특성 인자들의 대칭적 분포 경향에도 불구하고 그들의 절대값은 노즐 오리피스 중심축을 기준으로 대칭이 아니다.

• 설비공학논문집
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• 제3권4호
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• pp.222-230
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• 1991

Conjugate heat transfer by steady laminar natural convection from a conducting tube with two vertical axial fins has been studied by a finite difference numerical procedure under basic conditions; $Ra=10_6$, Pr = 5 and $L_F=0.15$. The maximum local tube Nusselt number appears at ${\theta}=140^{\circ}$ for $L_F=0.06$, at ${\theta}=130^{\circ}$ for $L_F=0.30$ and at ${\theta}=120^{\circ}$ for $L_F=0.30$, $L_F=0.06$, respectively. The maximum mean Nusselt number shows at $L_F=0.18$ for the downward fin and at $L_F=0.12$ for the upward fin. Therefore the optimized fin length is $L_F{\approx}0.15$ under these conditions. At $L_F=0.15$, the mean Nusselt number by increasing Rayleigh number is remarkably increased for downward fin and then is slowly increased except for downward fin, it by increasing Prandtl number is apparently increased at $Pr{\leq}2$, and slightly increased at Pr>2.

• 한국화재소방학회논문지
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• 제12권1호
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• pp.3-8
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• 1998

전자산업은 장치의 소형경량화를 추구하면서 단위체적당 발생하는 열량이 중가하는데 이때 발생하 는 열의 냉각문제는 전자산업의 발전에 있어서 해결해야될 중요한 품제로 풍장하고 있다. 대류냉각 방 식 은 구조가 간단하고 가격이 져렴 하면서도 사용이 편리하기 때문에 전자기기의 냉각방식으로 많이 사용되고 있다. 이때 효율적인 냉각을 위하여 전열면적의 확장 및 대류유동이 찰 이루어지는 기하학적 형상이 제안되고 있다. 전자기기에서 발생되는 열을 효과적으로 냉각시키기 위한 냉각핀에서의 대류열 전달 특성을 고찰하기 위하여 공기중의 청상충류 상태에서 둥온으로 가열된 경사명판에 수칙으로 부착 된 명판핀에 대하여 무차원 핀길이 HIS, 경사각, Grashof수.변 화에 따른 자연대류 열전달 특성올 비 교 분석한 결과는 다음과 같다. 평균 열전달계수는 무차원 핀길이 HIS가감소하거나Grashof수가충 가하면 대류유동이 촉진되기 때문에 중가되는 경향을 나타내었고, 경사각이 중가되면 대류유동에 장애 를 받기 때문에 감소하는 경향을 나타내었다.

• 대한치과교정학회지
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• 제49권6호
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• pp.360-371
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• 2019

Objective: We sought to determine the predictors of midpalatal suture expansion by miniscrew-assisted rapid palatal expansion (MARPE) in young adults. Methods: The following variables were selected as possible predictors: chronological age, palate length and depth, midpalatal suture maturation (MPSM) stage, midpalatal suture density (MPSD) ratio, the sella-nasion (SN)-mandibular plane (MP) angle as an indicator of the vertical skeletal pattern, and the point A-nasion-point B (ANB) angle for anteroposterior skeletal classification. For 31 patients (mean age, 22.52 years) who underwent MARPE treatment, palate length and depth, MPSM stage and MPSD ratio from the initial cone-beam computed tomography images, and the SN-MP angle and ANB angle from lateral cephalograms were assessed. The midpalatal suture opening ratio was calculated from the midpalatal suture opening width measured in periapical radiographs and the MARPE screw expansion. Statistical analyses of correlations were performed for the entire patient group of 31 subjects and subgroups categorized by sex, vertical skeletal pattern, and anteroposterior skeletal classification. Results: In the entire patient group, the midpalatal suture opening ratio showed statistically significant negative correlations with age, palate length, and MPSM stage (r = -0.506, -0.494, and -0.746, respectively, all p < 0.01). In subgroup analyses, a strong negative correlation was observed with the palate depth in the skeletal Class II subgroup (r = -0.900, p < 0.05). Conclusions: The findings of this study indicated that age, palate length, and MPSM stage can be predictors of midpalatal suture expansion by MARPE in young adults.

• 수산해양기술연구
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• 제35권4호
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• pp.404-409
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• 1999

The in situ target strengths of, maurolicus muelleri were measured by the split beam echo sounder system at the frequency of 38kHz.Target strengths were measured during the night time in order to obtain the pure separated echoes from the scattered individual. And also it was to establish reasonable threshold due to taking the signals like as the planktons and etc.Since Maurolicus muelleri is a typical micronektonic fish, they mainly consisted of deep scattering layers(DSLs), and had a vertical migration perrodically during daytime and at night.We found that the Maurolicus muelleri occupied about 99% of total catch. Total length ranged from 4.5 to 5.7cm with a mean of 5.2cm and a standard deviation of 0.22cm.The target strengths of Maurolicus muelleir ranged from -60.4 to - 52.7dB and -59.2 to - 52.5 dB in the water layer of 10~30m and 30~50m depth, perspectively. Mean target strength was -57.1dB/fish and -28.5dB/kg. The target strength had the relation with the total length of the fish as, TS=20logL-71.4.

• Wind and Structures
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• 제15권1호
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• pp.1-15
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• 2012

High-resolution wind data were acquired from a 100-m high offshore tower during the passage of Typhoon Hagupit in September, 2008. The meteorological tower was equipped with an ultrasonic anemometer and a number of cup anemometers at heights between 10 and 100 m. Wind characteristics of the strong typhoon, such as mean wind speed and wind direction, turbulence intensity, turbulence integral length scale, gust factor and power spectra of wind velocity, vertical profiles of mean wind speed were investigated in detail based on the wind data recorded during the strong typhoon. The measured results revealed that the wind characteristics in different stages during the typhoon varied remarkably. Through comparison with non-typhoon wind measurements, the phenomena of enhanced levels of turbulence intensity, gust factors, turbulence integral length scale and spectral magnitudes in typhoon boundary layer were observed. The monitored data and analysis results are expected to be useful for the wind-resistant design of offshore structures and buildings on seashores in typhoon-prone regions.

• Journal of Chest Surgery
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• 제33권1호
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• pp.20-25
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• 2000

Background: Median sternotomy remains the standard approach used by surgeons for most intracardiac operations but the residual scar is cosmetically unsatisfactory. To avoid an unsightly midline scar we have tried to use alternative skin incision (bilateral subm-ammary skin incision) to median sternal skin incision, In this study we have tried to compare different postoperative results of wound between two different skin incisional methods. Material and Method: Between June 1997 and June 1998, a bilateral subma-mmary skin incision combined with vertical sternotomy was performed in 21 pediatric female patients (submammary group)to repair acyanotic congenital heart disease. after the period we carried out a retrograde study about postoperative wound states comparing this incision with median sternal skin incision controls in whom there were 23 pediatric pat-ients (control group). Result: Patients' age ranged from 14 to 96 months(mean 38.2 months) Mean duration of subcutaneous drains using Hemovac which was used only in the patients of submammary group was 4.2 days and total amount of the drained effusion was 51.1 ml. Postoperative wound complications included wound eruption in one patient wound disruption in one patient and skin necrosis in 3 patients in submammary group and included wound disruption in 4 patients in controls. mean duration required for wound healing was 15,5 days in submammary group versus 10.4 days in controls. The mean scar length was 12.5 cm in submammary group versus 11.3 cm in controls. The average follow-up was 8.2 months in submammary group versus 9.0 months in controls. In submammary group 3 patients parents(14.3%) were pleased with their cosmetic results of wound scar but 8(38.1%) were dissatisfied. Among the 23 patients in control group 8(34.8%) were pleased but 8(34.8%) complained ofunhappiness with the scar.

• Water Engineering Research
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• 제3권4호
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• pp.235-245
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• 2002

In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of flow of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in 0.3 $\leq$ x/$\l_q$ $\leq$ 17. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157~0.190.

• 한국환경과학회지
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• 제11권10호
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• pp.1039-1044
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• 2002

In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of zone of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in $0.3{leq}x/I_p{leq}17$. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1340-1346
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• 1999

The turbulent shear flow around a surface-mounted vertical fence was investigated using the two-frame PTV system. The Reynolds number based on the fence height(H) was 2950. From this study, it is revealed that at least 400 instantaneous velocity field data are required for ensemble average to get reliable turbulence statistics, but only 100 field data are sufficient for the time-averaged mean velocity information. Various turbulence statistics such as turbulent intensities, turbulence kinetic energy and Reynolds shear stress were calculated from 700 instantaneous velocity vector fields. The fence flow has an unsteady recirculation region behind the fence, followed by a slow relaxation to the flat-plate boundary layer flow. The time-averaged reattachment length estimated from the streamline distribution is about 11.2H. There exists a region of negative Reynolds shear stress near the fence top due to the highly convex (stabilizing) streamline-curvature of the upstream flow. The large eddy structure in the separated shear layer seems to have significant influence on the development of the separated shear layer and the reattachment process.