• 설비공학논문집
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• 제12권8호
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• pp.771-781
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• 2000

The Karman boundary-layer, has been numerically investigated for the disturbance wave number, wave velocity, azimuth angle and radius (Reynolds number, Re). The disturbed flow over rotating disk can lead to transition at a much lower Re than that of the well-known Type 1 mode of instability. This early transition is due to the excitation of the Type II mode. Presented are the neutral stability results concerning these modes by solving new formulated vorticity equations with consideration of whole convective terms. When the present numerical results are compared with the previously known results, the value of critical Re corresponding to Type I is moved from Rec,! =285.3 to 270.2 and the value corresponding to Type II is from $Re_{c,2}$=69.4 to 36.9, respectively. Also, the corresponding wave number is moved from $k_1$ =0.378 to $k_1$ =0.389 for Type I; from $k_2$ =0.279 to $k_2$=0.385 for Type II. For Type II, the upper limit of wave number and azimuth angle is $k_U$=0.5872,$varepsilon_U=-18^{\circ}$ , while its lower limit is$k_L$ =0.05, $varepsilon_L=-27^{\circ}$ This implies that the disturbances will be relatively fast amplified at small Re and within narrow bands of wave number compared with the previous results.

• International Journal of Aeronautical and Space Sciences
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• 제13권1호
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• pp.64-73
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• 2012

Pointing stability of high precision observation satellites must satisfy the stringent requirements to perform at a designed level. As even a small vibrational disturbance can result in severe degradation of the optical performance, the effects of inorbit vibrational environment on the performance of optical payload must be predicted and analyzed in the design phase in order to ensure that the requirements imposed on the payload are fully met. In this paper, an integrated framework for the evaluation of the performance of optical payloads is developed. The developed simulation tool comprises of the reaction wheel induced disturbance model, state space model of a structure in modal form and Cassegrain reflector model. The performance degradation of the optical system due to jitter is expressed by using modulation transfer function (MTF) and image simulation. Moreover, vibration isolator model is also added to show the effectiveness of using a vibration isolator for the elimination of the effects of jitter in the acquisition of an image.

• 대한한방내과학회지
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• 제22권2호
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• pp.257-262
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• 2001

Cheiro-oral syndrome is characterized by a partial sensory disturbance in one hand and the ipsilateral oral comer. Its lesion is on the sensory track, and it is comparatively small. Most studies are case studies. These studies reported less than 10 cases. We studied two cases. In one, we observed intracranial hemorrhage involving left thalamus, posterior limb of internal capsule about 5cc in brain computed tomographic scan. The case was shown paresthesia of the right hand and ipsilateral comer of the mouth. The patient also complained about disturbing dysstereognosis and disorder of graphaesthesia. In the other case, we observed nodular calcification at the left basal ganglia external capsule in brain computed tomographic scan. The patient also complained about dysesthesia of the right thumb and index finger, fatigue and verbal disturbance. These cases appeared to be typical strokes in the acute phase, but after acute phase, they had dysethesia in the hand and periord for three months.

• 한국소음진동공학회논문집
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• 제20권3호
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• pp.215-222
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• 2010

Long and slender body, like a fuel rod, oscillating in axial flow can be unstabilized even by the small cross flow which can be activated by the flow mixer or turbulent generator. It is important to include these effects of flow disturbance in dynamic stability analysis of nuclear fuel rod. This work shows how eigen frequency of a multi-span fuel rod can be changed by the swirl flow, which is discretely generated by a flow mixer. By solving a state-space form of the eigenvalue equation for a multi-span fuel rod system, the critical velocity at which a fuel rod becomes unstable was calculated. Based on the simulation results, we evaluated how stability of a multi-spanned nuclear fuel rod with mixing vanes can be affected by the coolant flow in an operating reactor core.

• 드라이브 ㆍ 컨트롤
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• 제16권2호
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• pp.72-79
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• 2019

Despite the development of electronic components and microprocessors, hydraulic actuators are still being applied in various applications. In some applications, there is a desire to apply a hydraulic actuator with a relatively small position error to the system. Various studies have been conducted to reduce the position error of hydraulic actuators. In this paper, the position error of the hydraulic actuator when the hydraulic oil pressure is supplied is defined as the offset generated by the servo valve, and the method for correcting the servo valve offset has been studied. A method for compensating the servo valve offset was proposed and it was verified through experiments that the position error of the hydraulic actuator was reduced. We also compared the servo valve offset correction method and controller using the PID control and disturbance observer used to reduce the position error of the hydraulic actuator. No-load test and load test were performed to confirm the performance of the servo valve offset correction method. The results of the study were compared with those obtained by using the disturbance observer and PID control.

• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.317-322
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• 2012

The low speed aerodynamic characteristics for a modified sonic arc airfoil which is designed by using the nose shape function of sonic arc, the shape function of NACA four-digit wing sections, and Maple are experimentally investigated. The small rotor blades of a modified sonic arc and NACA0012 airfoil are precisely fabricated with a commercially available light aluminum(Al 6061-T6) and are spin tested over a low speed range (3000rpm-5000rpm). In a consuming power comparison, the consuming powers of NACA0012 are higher than that of modified sonic arcs at each pitch angle. The measured rotor thrust for each pitch angle is used to estimate the rotor thrust coefficient according to momentum theory in the hover state. The value of thrust coefficients for both two airfoils at each pitch angle show almost constant values over the low Mach number range. However, the rotor thrust coefficient of NACA0012 is higher than that of the modified sonic arc at each pitch angle. In conclusion, the aerodynamic performance of NACA0012 is better than that of modified sonic arcs in the low speed regime. This test model will provide a convenient platform for improving the aerodynamic performance of small scale airfoils and for performing design optimization studies.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제1권2호
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• pp.119-124
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• 1997

Cloud streets were successfully simulated by numerical model (RAMS) including an isolated mountain near the coast, large sensible heat flux from the sea surface, uniform stratification and wind velocity with low Froude number (0.25) in the inflow boundary. The well developed cloud streets between a pair of convective rolls are simulated at a level of 1 km over the sea. The following five results were obtained: 1) For the formation of the pair of convective rolls, both strong static instability and a topographically induced mechanical disturbance are strongly required at the same time. 2) Strong sensible heat flux from the sea surface is the main energy source of the pair of convective rolls, and the buoyancy caused by condensation in the cloud is negligibly small. 3) The pair of convective rolls is a complex of two sub-rolls. One is the outer roll, which has a large radius, but weak circulation, and the other is the inner roll, which has a small radius, but strong circulation. The outer roll gathers a large amount of moisture by convergence in the lower marine boundary, and the inner roll transfers the convergent moisture to the upper boundary layer by strong upward motion between them. 4) The pair of inner rolls form the line-shaped cloud streets, and keep them narrow along the center-line of the domain. 5) Both by non-hydrostatic and by hydrostatic assumptions, cloud streets can be simulated. In our case, non-hydrostatic processes enhanced somewhat the formation of cloud streets. The horizontal size of the topography does not seem to be restricted to within the small scale where non-hydrostatic effects are important.

• 한국항공우주학회지
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• 제33권8호
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• pp.75-83
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• 2005

확대형 채널 내의 정상 천음속 희박 예혼합 연소에 대해 점근해석을 이용하여 연구하였다. 이 모델은 근음속의 유동 속도와 일직선 채널로부터 벗어난 작은 형상변화 그리고 1단 1차 Arrhenius 화학 반응율에 의한 적은 열 방출 사이에서 일어나는 비선형 상호작용에 대하여 탐구하였다. 반응유체 유동은 연소 가스의 질량 분율을 계산하는 상미분 방정식과 연계된 비균질 천음속 미교란 방정식(TSD)을 사용하여 묘사하였다. 또한 점근해석으로부터 반응유체 유동 문제를 지배하는 상사 파라미터들을 유도하였다. 수치 결과들은 대류와 화학반응 그리고 형상효과 사이에 일어나는 복잡한 비선형 상호작용과 유동에 미치는 이것의 영향 등이 잘 나타나 있다.

• 한국임상수의학회지
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• 제24권2호
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• pp.218-224
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• 2007

소동물 임상에서 디지털 심전도기가 일반 아날로그 방식의 심전도기를 빠르게 대체하고 있다. 이러한 디지털 심전도기는 일반 아날로그 방식의 심전도기에 비해서 심전도 자료의 저장 능력, 이동성 및 넓은 임상적 적용 범위를 갖는 장점이 있다. 본 연구에서는 소동물 임상에 있어서 이러한 디지털 심전도기의 유용성을 연구하였고, 실제 심장전도계 장애가 있는 4마리의 개를 진단하고 치료하였다.

• 대한한방내과학회지
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• 제15권2호
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• pp.383-417
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• 1994

By making use of the EAV(Electroacupuncture acc. Voll) combined meridian theory of oriental medicine with electronics which was contrived to recognize the physiological and pathological changes of human body, the following conclusions were made in comparison with EAV measurements and types of symptoms(anxiety & headache, fatigue, palpitation, dizzness, abdominal distension. nausea, gastric disturbance. constipation & diarrhea, fatty liver, cva), QSCC, and blood type test. 367 patients including 124 with nervous gastrointestinal problems were selected for this research. 1. From the point of variance of the tested patients 124 nervous gastrointestinal patients, Liver meridian and Spleen meridian showed hyperenergia and Large intestine meridian, Circulation meridian, Triple warmer meridian showed hypoergia 2. In each symptom as the nervous gastrointestinal symptom Liver meridian showed hyperenergia, Large intestine meridian, Circulation meridian and Triple warmer meridian showed hypoergia . 3. In an objective comparison with other symptoms, firstly among the headache & anxiety group left Gall Bladder, Triple warmer and Stomach meridian showed remarkable hypoergia, secondly among fatigue group showed hypoergia in Triple warmer meidian and hyperenergia of Stomach meridian. and thirdly among palpitation group showed hypoergia of Kidney meridian, and lastly among dizzness group showed hypoergia of Gall Bladder, Stomach, Circulation and Small intestine meridian. 4. All of gastric disturbance, nausea, abdominal distention, constipation and diarrhea group showed hyperenergia in Stomach meridian and Spleen meridian. gastric disturbance group showed remarkably hypoergia in Circulation. Small intestine, Lung and Large intestine meridian. Nausea group showed hypoergia in Gall bladder and Urinary bladder meridian. Abdominal distenton group showed hypoergia of Large intestine. Constipation and diarrhea group showed hypoergia of Kidney and left Circulation meridian. 5. Fatty liver group showed hyperenergia of Liver meridian of 83.3%, Gall Bladder, Stomach and Spleen meridian. Urinary bladder and Kidney meridian showed hypoergia 6. CVA group showed hyperenergia in Liver and Circulation meridian. 7. Blood type in typical classification had no significant bearings on each other. 8. QSCC for the attempt of objective materials of constitutional diagnosis had no correlativity in comparison with EAV measurements. In conclusion EAV is thought be used as a diagnostic method in oriental medicine and further research is needed regarding it can be used as a useful method for verifying the characteristics and early finding of symptoms.