• 대한기계학회논문집B
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• 제20권2호
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• pp.697-709
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• 1996

Supersonic axisymmetric jets issuing from various kinds of nozzles with a throat diameter of a few millimeters were experimentally investigated. The exit Mach number and Reynolds number based on the throat diameter of nozzle were in the range of 1.0 ~ 5.9 and 8.4$\times$ $10^4$ ~ 2.9$\times$$10^6$, respectively. The nozzle pressure ratio was varied from 5 to 85. Present paper aims to offer fundamental information of the supersonic free-jets, with an emphasis to give data with which the shape of the free-jets can be depicted under a specified condition. Experimental data are summarized to enable an estimation of the shape of the supersonic free-jets. The result shows that the shape of free-jets is dependent on only the nozzle pressure ratio.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.570-573
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• 2012

고고도 모사를 위한 축소형 디퓨저의 성능특성을 파악하기 위해 수치적 연구를 수행하였다. 입구길이를 노즐 출구직경과 비교해 0%, 50%, 100%로 변화시켰고, 디퓨저 목의 길이는 디퓨저 목의 직경과 비교해 3, 5, 7, 8, 12로 다양화하여 수치해석하고 실제 모사실험 값과 비교하였다. 그 결과 디퓨저의 입구길이가 짧아질수록 plume의 형상은 수축되었다. 또한, 디퓨저의 이차목 길이가 디퓨저 지름의 최소 7~8배보다 작으면 내부에 마하디스크가 형성되어 압력의 급격한 상승을 일으킨다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.331-336
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• 2002

Recently the critical nozzles with small diameter are being extensively used to measure mass flow in a variety of industrial fields and these have different configurations depending on operation condition and working gas. The curvature radius of the critical nozzle throat is one of the most important configuration factors promising a high reliability of the critical nozzle. In the present study, computations using the axisymmetric, compressible, Navier-Stokes equations are carried out to investigate the effect of the nozzle curvature on critical flows. The diameter of the critical nozzle employed is D=0.3mm and the radius of curvature of the critical nozzle throat is varied in the range from 1D to 3D. It is found that the discharge coefficient is very sensitive to the curvature radius(R) of critical nozzle, leading to the peak discharge coefficient at R = 2.0D and 2.5D, and that the critical pressure ratio increases with the curvature radius.

• 한국항공우주학회지
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• 제35권4호
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• pp.281-286
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• 2007

노즐 목과 출구의 면적비가 1.8인 소형 2차원 초음속 노즐에 대해서 Navier-Stokes 방정식을 수치계산으로 풀었다. 압력비와 노즐 확대부 길이를 변화시킨 경우에 대해서 해석하여 노즐 안과 출구 근처에서 충격파 구조를 살펴보았고 특히 노즐 목 근처에서 발생하는 불규칙한 압력 분포의 특성을 노즐 목 근처의 기하학적 모양에 근거해서 규명하였다. 각각 독립적으로 표준형 노즐에서 압력비를 변화시킨 경우와 압력비를 고정하고 확대부의 노즐 길이를 변화시킨 경우 사이에 서로 유사한 충격파 구조 변화가 관찰되었고 여기에서 한 개의 경사 충격파로 오인될 수 있는 서로 다른 경사 충격파에 의해 만들어지는 수직 충격파도 포착하였다.

• 대한치과의사협회지
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• 제51권9호
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• pp.511-517
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• 2013

To assess the association between oral health and general health, this study examined the relationship between chewing difficulty and twelve chronic health conditions such as hypertension, hyperlipidemia, diabetes, cerebro- and cardiovascular disease, musculoskeletal disease, respiratory disease, eye/nose/throat disease, stomach/intestinal ulcer, renal dysfunction, thyroid disease, depression, and cancer in Korea. The study population was 3,066 elders aged 65 years old and more from the fourth Korean National Health and Nutrition Examination Survey. Chewing difficulty was measured on a 5-point Likert scale. Chronic conditions were assessed by self-reported questionnaire. Confounders were age, gender, education, income, smoking, drinking, and obesity. Chi-square test, general linear model, and multiple logistic regression model were done with complex sampling design. Musculoskeletal disease (adjusted odds ratio=1.33), respiratory disease (adjusted odds ratio=1.52), and cancer (adjusted odds ratio=1.58) were independently associated with chewing difficulty. Multiple chronic conditions with more than 4 chronic disease showed significant association with chewing difficulty (adjusted odds ratio=1.37).

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.469-474
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• 2005

전산화 단층촬영법을 이용하여 탄소/탄소 목삽입재의 밀도 분포를 평가 하였다. 전산화 단층촬영 법의 Beam hardening, 전기적 잡음 및 산란 X-ray의 영상을 토정하고 신호 대 잡음비를 높여 최적화할 때 측정된 제작된 탄소/탄소 복합재료의 밀도는 98.74%의 신뢰도 수준에서 ${\pm}0.01g/cm^3$ 분포를 갖는 것으로 평가 되었다. 전산화 단층촬영 결과의 검증은 탄소/탄소 목삽입재를 절단하며 수침법에 의한 밀도 측정과 주사전자현미경 관찰을 통하여 수행되었으며 단층촬영결과는 수침법에 의한 밀도 분포와 주사전자현미경의 결과와 일치하였다.

• Asian Pacific Journal of Cancer Prevention
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• 제15권14호
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• pp.5701-5707
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• 2014

Background: Salivary gland tumours, which account for approximately 3% of head-neck cancers, are a heterogeneous group and thus it is difficult to identify their epidemiological characteristics. The aim of this study is to determine demographic features and histopathologic distribution of parotid neoplasms in a large sample from Turkey. Materials and Methods: This study was conducted retrospectively on 136 parotidectomy materials from operations between May 2009-May 2013. Age, gender, tumor diameter, histopathological diagnosis and surgical margin status were recorded. Results: The benign cases were 112 (82.4%), while the malignancies were 24 (17.6%). The accuracy rate of FNAC was 91%. There were 46 (33.8%) male and 90 (66.2%) female patients. Female/male ratio (M/F=0.5) was two, the Warthin (WT) tumor being more apparent in males (p<0.05). Pleomorphic adenoma (PA) was detected most frequently among benign pathologies at 61.6% (69/112), while the Warthin Tumor (WT) was detected as the second most frequent tumor at 20.5% (23/112). Mucoepidermoid carcinoma (MEC) and carcinoma ex pleomorphic adenoma (Ca ex PA) were detected at equal frequency at 20.8% (5/24) among malign tumors. These were followed by acinic cell carcinoma at 16.7% (4/24). While the surgical margin was positive in ten patients with malignant tumors (41.7%), all of the benign tumors were negative (p<0.01). No significant difference was detected in the age-gender of patients, tumor size and distribution of sites among benign and malignant groups (p>0.05). Conclusions: Pleomorphic adenoma is the most frequently reported benign tumor almost in all global literature. Yet, the distribution of malignant tumors displays geographical differences. Based on these data, we believe that our findings will provide a significant contribution to future epidemiological studies. We think that it will be beneficial to generate awareness on parotid tumors and ensure a fight against smoking as with all head-neck cancers.

• Journal of Welding and Joining
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• 제12권1호
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• pp.102-115
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• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3191-3196
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• 2007

The present study addresses a method to operate a fuel-cell system effectively using a recirculation ejector which recycles wasted hydrogen gas. Configuration of a recirculation ejector is changed to investigate the flow behavior through it under varying operating conditions, and how such conditions affect the fuel-cell hydrogen cycle. The numerical simulations are based on a fully implicit finite volume scheme of the axisymmetric, compressible, Reynolds-Averaged, Navier-Stokes equations for hydrogen gas, and are compared with available experimental data for validation. The results show that a hydrogen recirculation ratio is effectively controlled by a configurational alteration within the operational region in which the recirculation passage doesn't plugged by a sonic line.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.54-59
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• 2000

A numerical study of axisymmetric rocket main nozzle flow has been accomplished. The CSCM upwind flux difference splitting method with an iterative time marching scheme having second order accuracy in time and space has been used to simulate unsteady flow characteristics in an axisymmetric rocket main nozzle. Though the pressure vary at nozzle inlet with the lapse of time, Mach No. and the density were not changed significontly compared with the temperature. Specific heat ratio $\gamma$=1.134 predicted higher temperature at nozzle throat and exit and nondimensional thrust coefficients at exit than specific heat ratio $\gamma$=1.4 did.