• 대한방사선기술학회지:방사선기술과학
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• 제31권4호
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• pp.379-387
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• 2008

반접현상(Aliasing)을 제거하기위한 방법 중 속도범위(velocity scale)를 높이는 방법은 동일 조건하에서 속도범위를 높여줌으로써 혈류의 방향이 반대로 나타나는 현상이 점차 사라지는 것을 확인할 수 있었다. Doppler angle을 $0^{\circ}$에 가깝게 하는 실험에서는 각도의 변화에 따른 스펙트럼 파형에서 유의한 차이점을 발견을 하지 못했다. 실제 초음파 검사(Ultrasonography)를 시행할 때는 검사의 편의성과 신속성, 정확성을 고려해서 속도범위에 변화를 주어 검사함으로써 보다 정확한 검사가 시행되리라고 본다. 또한 Doppler Angle에 따라 혈류속도는 기하학적으로 증가하였으며, $70^{\circ}$ 이상에서는 측정불가능 할 정도로 수치가 급상승하여 혈류속도가 Doppler Angle에 크게 의존한다는 것을 알 수 있었다. 혈류의 방향에 따른 실험에서는 입사각이 $60^{\circ}$ 이상에서 오차범위가 증가하였고, $70^{\circ}$ 이상에서는 매우 큰 차이를 보였다. 따라서 입사각은 $60^{\circ}$ 이하가 적당하다고 보며, 사지 혈관(extremity vessel)의 혈류속도를 구하는 데 있어서 Doppler 각도는 $45^{\circ}$에서 $60^{\circ}$가 적절한 것으로 사료된다.

• 한국운동역학회지
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• 제17권3호
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• pp.31-39
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• 2007

The purpose of this study was to observe the kinematic pattern of elite women 100m hurdler race from start to finish and analyze how the change of horizontal velocity makes an influence on the athletes' performance. The analysis was based on the performance of Korean elite 100m hurdler A and international elite hurdlers B and C. Following results were drawn from the analyzation of elite 100m hurdlers' technical characteristics; During the race, hurdler A made more than 8 m/s of horizontal velocity at the 3rd, 4th, 6th, and the 7th hurdle. The horizontal velocity peaked at the 4th hurdle with 8.23 m/s. On the other hand, hurdler B and hurdler C maintained more than 8 m/s of horizontal velocity from the 2nd hurdle through the 10th hurdle. Hurdler B's fastest horizontal velocity was 8.67 m/s from the 6th to the 7th hurdle and hurdler C's fastest horizontal velocity was 8.85 m/s from the 5th to the 8th hurdle. From the start line to the 3rd hurdle, the times achieved by hurdlers A, B, and C were 4.90 sec, 4.65 sec, and 4.52 sec. In the middle of the race, which is from the 4th hurdle to the 7th hurdle, hurdlers A, B, and C ran in 9.10 sec, 8.60 sec, and 8.38 sec. And the latter part of the race to the 10th hurdle, the times hurdlers A, B, and C hit were 12.32 sec, 11.66 sec, and 11.32 sec. To the finish line, it took 1.15 sec for hurdler A, 1.1 sec for B, and 1.06 sec for C. Hence, to set the record of sub-13 sec, hurdler A should improve her acceleration from the start line to the 1st hurdle with the speed more than 5.4 m/s and should maintain more than 8 m/s of horizontal velocity from the 2nd hurdle through the 10th hurdle. In addition, hurdler A should improve her speed endurance to minimize the deceleration of horizontal velocity from the 4th hurdle to the final hurdle. If hurdler A could shorten 0.05 sec of time in each hurdle section, she would be able to set the record under 13 seconds.

• 한국추진공학회지
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• 제3권4호
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• pp.44-50
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• 1999

Unlike impinging Quadlet injector(OOOF type)에 대한 혼합효율, 혼합특성속도, 혼합특성속도효율을 연소성능을 예측하기 위해 비연소 실험을 통하여 구하였다. 모의 추진제는 물($H_2$O)와 케로신($CH_{1.97}$)을 사용하였고, 혼합상관인자로써 산화제, 연료 분류의 운동량비를 사용하였다. 인젝터 분무특성을 파악하기 위해 오리피스(orifice) 각 hole에 대한 유량계수, 분무형상, 질량분포 획득이 수행되어졌다. 연구 결과, 침투깊이는 혼합효율, 혼합특성속도, 혼합특성속도 효율에 영향을 미침을 알 수 있었다. 또한, 혼합효율 및 혼합특성속도 효율은 MR=1.67(TMR=2.5)에서 87%로 최대값을 가지며 산화제 과잉상태보다 연료 과잉상태에서 더 큰 감소율을 보였다.

• 지구물리
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• 제3권1호
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• pp.49-56
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• 2000

울산단층의 단층분절 연구의 일환으로, 울산단층의 파쇄대로 추정되는 경주-울산간 7번국도와 인접한 지역 17개 측점에서 워커웨이 자료를 획득하였으며, 1-48 m의 옵셋구간에서 기록된 굴절파의 속도이방성을 측정하였다. 기록된 굴절 P파 속도는 평균 1787 m/s로 기반암의 풍화층 상부에서 굴절된 파로 해석되며, 속도이방성은 평균 0.056으로 구조선이 예상주향방향과 일치함을 간접적으로 시사한다. 경상북도와 경상남도의 도경계선를 기준으로 남쪽에서는 예상주향방향의 속도가 예상 경사방향보다 빠른 정상적인 이방성을 보이나, 북쪽으로는 단층의 주향이 여러 방향으로 갈라져있거나, 예상경사방향으로 발달된 구조선이 많이 발달해 있을 가능성이 높은 것으로 분석되었다. 이는 단층이 도경계선 부근을 경계로 울산단층이 분절되어 있을 가능성을 시사한다.

• 대한치과보철학회지
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• 제27권2호
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• pp.143-154
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• 1989

The purpose of this study was to investigate the mandibular opening and closing movements at mandibular incisor region and clinical rest position in normal subject using the newly developed electric mandibular movement analyzing device, (M.K.G.-K6 diagnostic system, Myo-tronics Inc. Seattle, WA, U.S.A.) The 58 normal subjects, who were students of the College of Dentistry, Chonbuk National University, were selected according to sampling criteria. The obtained results were as follows: 1. There was no significant difference of distribution of opening and closing movement patterns at mandibular incisor region between male and female. There was significant difference between habitual and maximum movement patterns both in sagittal and frontal plane. 2. Although the percentage of distribution of crossover pattern was highest in all cases, but there were significant differences between patterns only at habitual opening and closing movement in sagittal plane. 3. The mean of maximum opening was $47.29{\pm}4.68mm$ in male and $42.15{\pm}4.95mm$ in female. Therefore the mean of maximum opening was larger in male than in female. 4. The mean of maximum laterotrusion in frontal trajectory was larger to the left than to the right. Also the proportion of left deviation at maximum opening position was larger than that of other cases. 5. The mean of maximum opening and closing velocity was higher in male than in female and the mean of closing velocity was higher than that of opening velocity. Also the amount of separation from the centric occlusion was higher in maximum closing velocity than in maximum opening velocity. 6. Clinical rest position was $1.70{\pm}0.99mm$ inferior, $0.74{\pm}0.57mm$ anterior, $0.99{\pm}0.51mm$ right from centric occlusion and the A/V ratio was 1:2.7.

• 한국지열·수열에너지학회논문집
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• 제12권4호
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• pp.40-46
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• 2016

In order to improve air quality of indoor environment, studies of the underfloor air distribution (UFAD) system for application in buildings are actively in progress based on temperature and air flow distribution. However, although the age of air is the major evaluation parameter, there has been very little study on this parameter for the UFAD system. In this study, we investigated the age of air to reach the air diffuser, which is installed at the bottom of the interior by the UFAD system. Computational fluid dynamics simulations showed no regular pattern to the maximum value of the age of air in accordance with air flow rate and the velocity at air diffuser. These factors can be deduced from air movement by considering that air emitted from air conditioners was rotated according to the bottom shape of the floor, and then, the age of air in the rotation center was increased. The average age of air of internal interior was reduced considerably as the flow velocity at the underfloor air diffuser was increased from 0.5 m/s to 1.0 m/s However, the age of air was not substantially affected with change in the air volume. Moreover, when the flow velocity at the underfloor air diffuser was higher than 1.0 m/s, the age of air showed no significant difference with change in air volume or height of measurement. These results imply that indoor air quality is more substantially influenced by flow velocity than air volume, and the appropriate flow velocity is 1 m/s or more.

• 한국소음진동공학회논문집
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• 제20권11호
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• pp.1078-1088
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• 2010

In order to analyze the quantitative characteristics of acoustic streaming, experimental setup of 3-D stereoscopic PIV(particle imaging velocimetry) was designed and quantitative ultrasonic flow fields in the gap between the ultrasonic vibrator and heat source were measured. Utilizing acoustic streaming induced by ultrasonic vibration, surface temperature drop of cooling object was also measured. The study on smart cooling method by acoustic streaming induced by ultrasonic vibration was performed due to the empirical relations of flow pattern, average flow velocity, different gaps, and enhancement on cooling rates in the gap. Average velocity fields and maximum acoustic streaming velocity in the open gap between the stationary cylindrical heat source and ultrasonic vibrator were experimentally measured at no vibration, resonance, and non-resonance. It was clearly observed that the enhancement of cooling rates existed owing to the acoustic air flow in the gap at resonance and non-resonance induced by ultrasonic vibration. The ultrasonic wave propagating into air in the gap creates steady-state secondary eddy called acoustic streaming which enhances heat transfer from the heat source to encompassing air. The intensity of the acoustic streaming induced by ultrasonic vibration experimentally depended upon the gap between the heat source and ultrasonic vibrator. The ultrasonic vibration at resonance caused the increase of the acoustic streaming velocity and convective heat transfer augmentation when the flow fields by 3D stereoscopic PIV and temperature drop of the heat source were measured experimentally. The acoustic streaming velocity of air enhancement on cooling rates in the gap is maximal when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which is specifically 12 mm.

• 대한기계학회논문집B
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• 제38권3호
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• pp.197-202
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• 2014

촉매 변환기의 효율은 촉매 물질이 포함되어 있는 하니콤 브릭 입구의 유동장 분포와 밀접한 관계가 있다. 하니콤 브릭 표면의 유동장 분포가 균일하지 않으면 시스템의 전환 효율이 감소하고 균일한 유동장 분포를 갖는 촉매 변환기에 비해 크기가 커져 제작비용도 증가한다. 따라서 촉매 변환기의 내부유동 해석은 매우 중요하다. 본 연구에서는 변환기 내부 하니콤 브릭 사이부분과 2번째 하니콤 브릭 출구부분의 유동분포를 단축을 따라 37.8 l/s와 94.4 l/s 유동영역에서 측정하였다. 또한, 자동차 제작사에서 이루어진 전산해석 결과를 측정 결과와 비교하여 실험적으로 검증하였다. 하니콤 브릭 사이부분의 ${\upsilon}$-속도분포 측정은 다소 변화하는 유동패턴이 형성되는 것을 보여주지만 입구 반대쪽 벽 부근영역에서 음의 유동장이 형성되고 음의 속도는 감소하여 중심 부근에서는 정체현상을 보이고 계속 입구 쪽까지 지속되는 것을 보여준다. 대부분의 속도 값에서 전산해석 결과는 측정치에 비하여 크게 나타났다.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.17-20
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• 2006

Passenger safety is fundamental factor in automobile. Among much equipment for passenger safety, the air bag system is the most fundamental and effective device. Beside of the front air bag system which installed on most of all automobiles, a curtain-type air bag is increasingly adapted in deluxe cars fur protecting passengers from the danger of side clash. Curtain type airbag system consists of inflator housing, fill hose, curtain airbag. Inflator housing is a main part of the curtain-type air bag system for supplying high-pressure gases to deploy the air bag-curtain. Fill hose is a passageway to carry the gases from inflator housing to each part of curtain airbag. Therefore, it is very important to design the vent holes of fill hose for good performance of airbag deployment. But, the flow information from vent holes of fill hose is very limited. In this study, we measured instantaneous velocity fields of a high-speed flow ejecting from the vent holes of fill hose using a dynamic PIV system. From the velocity Held data measured at a high frame-rate, we evaluated the variation of the mass flow rate with time. From the instantaneous velocity fields of flow ejecting from the vent holes in the initial stage, we can see a flow pattern of wavy motion and fluctuation. The flow ejecting from the vent holes was found to have very high velocity fluctuations and the maximum velocity was about 480m/s at 4-vent hole region. From the mass flow rate with time, the accumulated flow of 4-vent hole has occupied about 70% of total flow rate.

• 한국입자에어로졸학회지
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• 제18권4호
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• pp.129-136
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• 2022

The line width of circuits in semiconductor devices continues to decrease down to a few nanometers. Since nanoparticles attached to the patterned wafer surface may cause malfunction of the devices, it is crucial to remove the contaminant nanoparticles. Physical cleaning that utilizes momentum of liquid for detaching solid nanoparticles has recently been tested in place of the conventional chemical method. Dropwise impaction has been employed to increase the removal efficiency with expectation of more efficient momentum exchange. To date, most of relevant studies have been focused on drop spreading behavior on a horizontal surface in terms of maximum spreading diameters and average spreading velocity of drop. More important is the local liquid velocity at the position of nanoparticle, very near the surface, rather than the vertical average value. In addition, there are very scarce existing studies dealing with microdroplet impaction that may be desirable for minimizing pattern demage of the wafer. In this study, we investigated the local velocity distribution in spreading liquid film under various impaction conditions through the CFD simulation. Combining the numerical results with the particle removal model, we estimated an effective cleaning diameter (ECD), which is a measure of the particle removal capacity of a single drop, and presented the predicted ECD data as a function of droplet's velocity and diameter particularly when the droplets are microns in diameter.