• 설비공학논문집
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• 제13권3호
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• pp.209-216
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• 2001

A numerical study is peformed to investigate the effect of circumferential velocity generated by the guide vane on the nozzle flow of a jet fan, s a way of increasing the penetration force of jet fan with nozzle of 175mm diameter. For the validation of numerical results. the velocity is measured by a 5-hole pitot tube and flow visualization is conducted by the tuft method. Under the inlet condition that the maximum circumferential velocity in the stator outlet of the present jet fan is 1.8m/s, the axial velocity in the nozzle outlet has the feature that the velocity at the axis is low and the velocity near the wall high. Therefore, to increase the throw length of the jet fan, the configuration of the fairing and nozzle needs to be developed and the precise revise of the stator angle is required, In addition, the bigger the circumferential velocity, the smaller the axial velocity at the axis and the bigger non-uniformity of the flow distribution.

• Journal of applied mathematics & informatics
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• 제39권1_2호
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• pp.31-43
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• 2021

A homogeneous circular disk undergoing a contact force is considered to investigate the thermo-elastic characteristics, and the inquiry is based on the variations of outer surface temperature and angular velocity. The intensity of stresses grows with the increase of outer surface temperature, and the circumferential strain reacts more sensitively to the change of outer surface temperature than the radial strain. In general, higher angular velocity produces; (i) larger expansion in the radial direction, (ii) smaller displacement in the circumferential, (iii) diminished intensity in the stresses. It is demonstrated that outer surface temperature and angular velocity are critical factors in the determination of thermo-elastic characteristics of homogeneous circular disks subjecting to a contact force. The results obtained can be applied on the design of a homogeneous circular cutter to promote proper and reliable thermos-elastic characteristics in service by the proper operation of these parameters.

• 한국결정성장학회지
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• 제3권1호
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• pp.18-30
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• 1993

균일한 자장과 비균일한 자장이 도가니에 가하여졌을 때의 Czochralski유동장이 수치적으로 해석되었다. 여기에서 부력의 효과, thermocapillarity 효과, 원심력의 효과, 자장의 효과등이 Czochralski유동장을 지배하고 있다. 자오면에서의 속도성분과 회전방향의 속도성분이 구하여졌으며 온도, 전류의 흐름 등이 해석되었다. 균일한 자장의 경우에 세기가 증가하면 모든 속도성분이 작아지고 있으며 결정표면 아래에서 회전방향으로의 전류의 세기가 증가한다. 불균일한 자장의 경우에는 자장의 불균일성이 증가하면 자오면에서의 평면유동은 억제되는 반면 회전방향의 속도성분은 더 증가하게 된다. 이와 같은 여러 형태의 자장의 영향아래에서의 Czochralski 유동장에 대한 이해는 도가니(Crucible)안의 용질 및 불순물의 농도에 관한 거동을 연구할 수 있는 기초를 제공하고 있다.

• 터널과지하공간
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• 제8권3호
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• pp.226-233
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• 1998

자연적으로, 혹은 인위적으로 발생된 균열들은 현지암반의 공학적 거동에 대한 중요한 자료를 제공한다. 일정한 방향으로 분포하는 미세균열들은 암반의 물성에 현저한 영향을 미치게 되지만, 다른 요인들에 의한 이방성이 큰 경우에는 이들의 영향은 감소한다. 본 연구에서는 초음파속도의 이방성과 점하중 재하에 의한 인공균열의 진행방향을 기초로, 암석조직이 암석의 물성에 미치는 영향에 대하여 조사하였다. 암석시료는 우백질의 포천화강암 석재에서 코어링한 NX 시험편과 현장 시추코어를 사용하였다. 시료에 분포하는 균열들의 주 방향을 기준으로 설정한 후, 초음파속도의 이방성을 측정한 결과, 균열에 수직한 방향에서 초음파속도의 최소치가 측정되었다. 속도측정에 사용한 NX코어로부터 EX크기의 원판형 시험편을 성형한 수 점하중 재하실험을 수행하였으며, 점하중재하에 의한 인공균열의 진행방향은 기존의 미세균열의 방향과 거의 일치하였다.

• 대한기계학회논문집B
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• 제23권5호
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• pp.661-669
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• 1999

The evolutionary structure of a tip vortex in the initial period have been investigated by the two-dimensional LDV system. Circumferential and axial components of mean velocities, their turbulences and Reynolds stresses were measured by the phase averaging technique at seven different wake ages within one revolution of the rotor. Core growth was also analyzed. It was resulted that circumferential velocity components showed a Rankine combined vortex shape and their circulation profiles viewed in the radial direction were close to the n = 2 model of Vatistas' algebraic formula, while axial velocity components seemed to have the Gaussian profiles In these measured ranges with the base width of three times of core radii. Peaks of circumferential velocities and core radii showed distinct asymmetric behaviors before the wake age of $150^{\circ}$ over inboard and outboard sides of the slipstream, but they became symmetric afterwards. Turbulence profiles which had two peaks Inside the core radii in the earlier wake age were also changed to single peaks after $150^{\circ}$. These trends imply that the tip vortex was barely mature at this wake age.

• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.625-633
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• 2005

A finite element vibration analysis of thin-walled cylindrical shells conveying fluid with uniform velocity is presented. The dynamic behavior of thin-walled shell is based on the Sanders' theory and the fluid in cylindrical shell is considered as inviscid and incompressible so that it satisfies the Laplace's equation. A beam-like shell element is used to reduce the number of degrees-of-freedom by restricting to the circumferential modes of cylindrical shell. An estimation of frequency response function of the pipe considering of the coupled effects of the internal fluid is presented. A dynamic coupling condition of the interface between the fluid and the structure is used. The effective thickness of fluid according to circumferential modes is also discussed. The influence of fluid velocity on the frequency response function is illustrated and discussed. The results by this method are compared with published results and those by commercial tools.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.302-312
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• 2004

This work developed improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan. Both steady and unsteady three-dimensional CFD analyses were performed to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the present model takes into account the effect of blade curvature. The correction method is provided to predict mass-averaged absolute circumferential velocity at the exit of impeller by taking account of blockage effects induced by the large-scale backflow near the front plate and flow separation within blade passage. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.743-750
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• 2008

Asymmetric tip clearance in an axial compressor induces pressure and velocity redistributions along the circumferential direction in an axial compressor. This paper presents the mechanism of the flow redistribution due to the asymmetric tip clearance with a simple numerical modeling. The flow field of a rotor of an axial compressor is predicted when an asymmetric tip clearance occurs along the circumferential direction. The modeling results are supported by CFD results not only to validate the present modeling but also to investigate more detailed flow fields. Asymmetric tip clearance makes local flow area and resultant axial velocity vary along the circumferential direction. This flow redistribution 'seed' results in a different flow patterns according to the flow coefficient. Flow field redistribution patterns are largely dependent on the local tip clearance performance at low flow coefficients. However, the contribution of the main flow region becomes dominant while the tip clearance effect becomes weak as the flow coefficient increases. The flow field redistribution pattern becomes noticeably strong if a blockage effect is involved when the flow coefficient increases. The relative flow angle at the small clearance region decreases which result in a negative incidence angle at the high flow coefficient. It causes a recirculation region at the blade pressure surface which results in the flow blockage. It promotes the strength of the flow field redistribution at the rotor outlet. These flow pattern changes have an effect on the blade loading perturbations. The integration of blade loading perturbation from control volume analysis of the circumferential momentum leads to well-known Alford's force. Alford's force is always negative when the flow blockage effects are excluded. However when the flow blockage effect is incorporated into the modeling, main flow effects on the flow redistribution is also reflected on the Alford's force at the high flow coefficient. Alford's force steeply increases as the flow coefficient increases, because of the tip leakage suppression and strong flow redistribution. The predicted results are well agreed to CFD results by Kang and Kang(2006).

• 비파괴검사학회지
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• 제19권3호
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• pp.189-199
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• 1999

산화막이 피복된 원전 연료봉의 원통형 쉘에 대한 공명산란 해석을 수행하고 원주파 전파 특성을 연구하였다. 피복 쉘에 대한 산란 음압의 정규 모우드 해를 구하였고 최근에 새롭게 제안된 고유 배경음압 계수를 이용하여 피복 쉘의 순수 공명 신호를 분리하였다. 12%의 상대 두께를 갖는 원통형 피복 쉘에 대하여 산화막 두께 증가에 따른 공명 원주파의 전파 특성을 해석하였다. 산화막의 존재와 그 두께가 증가할 때 정규 모우드의 차수에 따라 원주파의 전파 특성이 크게 변화한다. 제 1차 반대칭 ($A_1$) 원주파에서 특정 부분파의 위상속도는 산화막이 존재하고 그 두께가 증가함에도 불구하고 위상속도가 일정 한 특성을 보인다. 공명신호를 분리하고 공명 모우드를 확인하는 실험을 수행하여 $A_1$ 원주파의 전파 특성을 확인하였다. $A_1$ 원주파의 위상속도 일정 특성을 이용함으로써 산화막의 두께를 상대적으로 측정 할 수 있는 새로운 비파괴 평가방법을 제안하였다.

• 대한수의학회지
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• 제37권3호
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• pp.669-685
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• 1997

The present study was performed to evaluate the effects of xylazine and tiletamine + zolazepam on echocardiograms before and after experimental myocardial infarctions in clinically normal dogs taken preliminary examinations related to cardiac function. The results are as follows. With xylazine administration, left ventricle end-diastolic dimension, left ventricle end-systolic dimension, left atrium/aorta, ejection time and velocity of circumferential fiber shortening increased and mitral valve CD slope, % delta D decreased(p<0.01). In tiletamine+zolazepam administered group, interventricular septum amplitude(p<0.01), mitral valve DE slope(p<0.05) and ejection time(p<0.01) decreased and left atrium/aorta, ejection time also decreased compared with xylazine group(p<0.01). In 48 hours after experimental myocardial infarction group, anterior aortic wall amplitude decreased compared with control, xylazine, tiletamine + zolazepam group, respectively(p<0.01). Posterior aortic wall amplitude decreased compared with control(p<0.01). Left ventricle end systolic dimension increased compared with control and tiletamine + zolazepam group, respectively(p<0.01). Left ventricular posterior wall end systolic dimension decreased compared with control(p<0.01). Left ventricular posterior wall amplitude decreased compared with control and tiletamine+zolazepam group(p<0.01). Left atrium/aorta decreased compared with xylazine group(p<0.01). % thickening left ventricular posterior wall decreased compared with control(p<0.05). % delta D decreased compared with control and tiletamine+zolazepam group(p<0.01). Ejection time decreased compared with xylazine(p<0.01). Velocity of circumferential fiber shortening increased compared with control and tiletamine + zolazepam group(p<0.01). With xylazine administration 48 hours after experimental myocardial infarction, anterior aortic wall amplitude, posterior aortic wall amplitude decreased compared with control(p<0.01). Left ventricle end-diastolic dimension increased compared with control(p<0.01). Left ventricle end-systolic dimension increased compared with control and tiletamine + zolazepam group, respectively(p<0.01). Left ventricular posterior wall end-systolic dimension and left ventricular posterior wall end-diastolic dimension decreased compared with control(p<0.01). Left atrium/aorta decreased compared with xylazine group(p<0.01). % thickening left ventricular posterior. wall(p<0.05) and % delta D(p<0.01) decreased compared with control. Velocity of circumferential fiber shortening increased compared with tiletamine + zolazepam group(p<0.01). With tiletamine + zolazepam administration 48 hours after experimental myocardial infarction, anterior aortic wall amplitude decreased compared with control, xylazine and tiletamine+zolazepam group, respectively(p<0.01). Posterior aortic wall amplitude decreased compared with control(p<0.01). Left ventricle end-systolic dimension increased compared with control and tiletamine+zolazepam group(p<0.01). Left ventricular posterior wall end-systolic dimension, left ventricular posterior wall end-diastolic dimension and interventricular septum amplitude decreased compared with control(p<0.01). Left atrium/aorta decreased compared with xylazine group(p<0.01). % delta D decreased compared with control and tiletamine + zolazepam group(p<0.01). Ejection time decreased compared with xylazine group and velocity of circumferential fiber shortening increased compared withtiletamine+zolazepam group(p<0.01). Conclusively, echocardiography was proved to be a useful, diagnostic, non-invasive and simple method for establishing the diagnosis of myocardial infarction and evaluating the effects of drug on cardiac function before and after myocardial infarction.