• Title/Summary/Keyword: laser Doppler

Search Result 480, Processing Time 0.025 seconds

Velocity Measurement in a Rectangular Duct with $90^{\circ}$ Mitered Elbow (직각 엘보우를 가진 사각덕트 내의 유속측정에 관한 연구)

  • 윤영환;배택희;박원구
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.13 no.12
    • /
    • pp.1184-1195
    • /
    • 2001
  • Analysis of fluid flow in rectangular ducts has been conducted since it has a wide application. The purpose is to provide experimental data for the comparison with computational results. Velocity distributions inside a rectangular duct with $90^{\circ}$ mitered elbow are measured by 5W laser doppler velocity meter for Reynolds numbers of 4,049, 8,104, and 12,186. Flow rates obtained by the integration of measured velocity profile at three cross-sections, which are inlet, middle section after the elbow, and outlet, have errors less than 0.9% among them. Turbulent fluctuation components in two directions are found to have almost similar magnitude each other at a certain location due to the isotropic characteristic of turbulence.

  • PDF

Experimental and Computational Studies for Flow Distribution In a Rectangular Duct System with Two Branches (두 개의 분지관을 가진 직사각형 덕트 내의 유량배분에 관한 실험 및 수치계산 연구)

  • 윤영환;배택희;박원구
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.14 no.9
    • /
    • pp.766-773
    • /
    • 2002
  • Flow distributions in a rectangular duct with two branch ducts are measured by 5 W laser doppler velocity meter. The fluid flows are also computed by commercial soft-ware of STAR-CD for comparison between them. The Reynolds numbers in the main duct are from 4,226 to 17,491. The ratios distributed into two branches from the main duct are in-variant to Reynolds numbers according to both of numerical and experimental results. However computed velocity profiles at exit of each branch are somewhat different from measured profiles at the same location.

Fabrication of Heterodyne type Laser Doppler Velocimeter and Studies of its Characteristics (Heterodyne type의 레이저 속도계 제작 및 특성연구)

  • 박형국;임충수;전형하;김달우;오기장
    • Proceedings of the Optical Society of Korea Conference
    • /
    • 2000.08a
    • /
    • pp.58-59
    • /
    • 2000
  • 레이저를 이용한 속도측정은 비접촉식 정밀측정이라는 장점 때문에 산업현장의 생산라인에서 온-라인 계측장비로 이용되고 있다. 특히, 철강업에서는 각종 설비의 제어를 위한 속도측정이나 연신률 측정 및 길이측정에 활용되고 있으며 제지분야나 고무생산 현장에서도 계측장비로 활용성이 점점 높아지고 있다. 본 연구는 레이저를 이용하여 비접촉식 속도계(Laser Doppler Velocimeter; LDV)를 제작하고 특성을 연구하였다. 기본 원리는 두 개의 레이저 빔을 측정대상의 한 지점에 입사시키고 이 지점에서 산란된 빛의 세기를 광검지기로 측정한 후 광검지기 출력의 주파수를 분석하여 측정대상의 속도를 산출하는 방법으로 두 개의 레이저 빔의 주파수가 같은 homodyne type과 주파수가 다른 heterodyne type으로 나누어지고 있다. Heterodyne type의 LDV 시스템은 속도값과 함께 측정대상의 이동방향을 알 수 있고, 측정신호가 고주파 대역에 있으므로 레이저의 불안정성이나 전원잡음 등에 의한 저주파 잡음을 용이하게 제거할 수 있는 장점을 가지고 있다. (중략)

  • PDF

Study on Fluid Flow in Rectangular Duct past $90^{\circ}$ Mitered Elbow (사각덕트내 직각엘보우를 지난 유체유동에 관한 연구)

  • 윤영환;배택희;박원구
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.26 no.6
    • /
    • pp.670-678
    • /
    • 2002
  • Fluid flow in a rectangular duct with $90^{\circ}$ mitered elbow is measured by 5W laser doppler velocity meter. The fluid flow is also computed by commercial software of STAR-CD for comparison between measured and computed velocity profiles in the duct. Reynolds numbers for the comparison are 1,608 and 11,751 based on mean velocity and hydraulic diameter of the duct. First, the fluid flow of Reynolds number equal to 1,608 is predicted by assumptions of both laminar and turbulent models. But, even though the Reynolds number is less than 2,300~3,000, the computation by turbulent model is closed to the experimental data than that by laminar model. Second, the computation for Reynolds number of 11,751 by turbulent model also predicted the experimental data satisfactorily.

Research on the Effect of Cutter Wear on the Torsional Vibration of Spindle in Milling (밀링가공에서 공구마모와 스핀들의 비틀림 진동과의 상관관계에 관한 연구)

  • Kim, Seog-Gwan
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.16 no.9
    • /
    • pp.62-67
    • /
    • 1999
  • In milling, cutting tool ins directly attached to spindle and this tells that spindle can provide very useful information on the cutting tool condition such as wear or breakage. Since spindle is rotating at a high speed, measuring spindle velocity using a noncontacting measurement system gives the best information which can be obtained. Due to the force applied to spindle through cutting tool, velocity of spindle changes. And any change in cutting tool condition affects cutting force and consequently spindle vibration. With the intent of continuously monitoring cutting tool condition in intermittent machining operations in a benign manner, a noncontacting velocity measurement system using a laser Doppler velocimeter was assembled to measure spindle torsional vibration. Spindle vibration was measured and analysis of it in the frequency domain yielded a measure which corresponded to amount of cutting tool wear in milling.

  • PDF

Study on Velocity Measurement and Numerical Computation in a Rectangular Duct with $90^\circ$ Bend Elbow (곡면 엘보우를 가진 사각덕트 내의 유속측정 및 수치계산에 관한 연구)

  • 윤영환;박원구
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.15 no.11
    • /
    • pp.910-917
    • /
    • 2003
  • Fluid flow in a rectangular duct for 90$^{\circ}$ bend elbow with the ratio of 1.5 between its curvature radius and width is measured by 5 W laser doppler velocity meter. The fluid flow is also computed by commercial software of STAR-CD for comparison between measured and computed velocity profiles in the duct. Reynolds numbers for the comparison are 11,643, 19,746 and 24,260. From the comparison, computation of principal velocity components in the duct predicts the experimental data somewhat satisfactorily even though those of minor velocity components and turbulent kinetic energy do not match with the experimental data quite well. K-factor for the bend elbow is computed to be average 0.086 while the equivalent ASHRAE data is 0.07.

Rail Inspection Using Noncontact Laser Ultrasonics

  • Kim, Nak-Hyeon;Sohn, Hoon;Han, Soon-Woo
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.32 no.6
    • /
    • pp.696-702
    • /
    • 2012
  • In this study, a noncontact laser ultrasonic system is proposed for rail defect detection. An Nd-Yag pulse laser is used for generation of ultrasonic waves, and the corresponding ultrasonic responses are measured by a laser Doppler vibrometer. For the detection of rail surface damages, the shape of the excitation laser beam is transformed into a line. On the other hand, a point source laser beam is used for the inspection of defects inside a rail head. Then, the interactions of propagating ultrasonic waves with defects are examined using actual rail specimens. Amplitude attenuation was mainly observed for a surface crack, and reflections were most noticeable from an internal damage. Finally, opportunities and challenges associated with real-time rail inspection from a high-speed train are discussed.

Noncontact Laser Ultrasonic Imaging for Automated Damage Detection (자동화 손상 검색을 위한 비접촉식 레이저 초음파 영상화)

  • Park, Byeong-Jin;An, Yun-Kyu;Sohn, Hoon
    • Proceedings of the Computational Structural Engineering Institute Conference
    • /
    • 2011.04a
    • /
    • pp.40-43
    • /
    • 2011
  • 최근, 레이저 초음파 영상화 기법은 구조물의 비접촉식 손상 진단을 위해 널리 연구되고 있다. 초음파 영상화 기법의 가장 큰 장점은 비접촉식으로 구조물의 손상을 진단할 수 있고, 가진 및 측정 지점을 자유로이 이동할 수 있다는 점이다. 따라서 이는 고온이나 동적상태의 구조물에 적용이 가능하며, 시간과 공간상의 충분한 데이터를 획득할 수 있으므로 역문제 (Inverse problem)를 해결할 필요 없이 완전한 초음파의 전파 형상을 얻을 수 있다. 지난 연구들에서는 충분한 가진력 혹은 측정 민감도를 확보하기 위해 가진 레이저와 부착형 센서의 조합이나 부착형 가진 트렌스듀서와 센싱 레이저의 조합으로 초음파 영상을 획득하고자 하였다. 하지만 이들 조합은 가진 혹은 측정 지점이 구조물에 부착되어 있어 완전한 비접촉식 기법을 구현하지 못하였다. 이를 극복하고자 레이저와 EMAT 센서 등의 조합이 시도되어 왔으나, 이 또한 EMAT 센서의 적용 거리에 따른 한계점을 지니고 있다. 본 연구에서는 가진 레이저 (Nd:Yag)의 스캐닝을 통해 다양한 가진 점에서 발생된 초음파가 탄성체 구조물을 통해 전파되고, 이를 센싱 레이저 (Laser Doppler Vibrometer)를 이용하여 측정함으로써 비접촉식 초음파 영상화를 구현하였다. 나아가, 정상파 필터(Standing-wave filter)를 이용하여 구현된 초음파 영상으로부터 손상 영향만 검출해 내는 기법을 개발했다. 개발된 기법은 복합재 시편의 층간박리 (Delamination) 진단을 통해 검증하였다.

  • PDF