• Title/Summary/Keyword: laser shock wave

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Flow Visualization Using Thin Oil-Film in the Flow Control of Shock Wave/Turbulent Boundary-Layer Interactions (충격파와 경계층 간섭유동 제어에서 오일막을 이용한 유동가시화)

  • Lee Yeol
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.117-120
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    • 2002
  • An experimental research has been carried out for flow control of the shock wave/turbulent boundary-layer interaction utilizing aeroelastic mesoflaps. Various shapes and thicknesses of the mesoflap are tested to achieve different deflections of the flap, and ail the results are compared to the solid-wall reference case without flow-control mechanism. Quantitative variation of skin friction has been measured downstream of the interactions using the laser interferometer skin friction meter, and qualitative skin friction distribution has been obtained by observing the interference fringe pattern on the oil-film surface. A strong spanwise variation in the fringe patterns with a narrow region of separation near the centerline is noticed to form behind the shock structure, which phenomenon is presumed partially related to three-dimensional flow structures associated with both the sidewalls and the bottom test surface. The effect of the shape of the cavity is also observed and it is noticed that the shape of the cavity is not negligible.

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Reliability and utility of a Dry Test Bench for testing the acoustic output from a ballistic shock wave therapeutic device (탄도형 충격파 치료기의 음향 출력 시험을 위한 Dry Test Bench의 신뢰성 및 유용성)

  • Jeon, Sung Joung;Lee, Min Young;Kwon, Oh Bin;Kim, Jong Min;Choi, Min Joo
    • The Journal of the Acoustical Society of Korea
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    • v.41 no.5
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    • pp.589-600
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    • 2022
  • In order to verify the reliability of Dry Test Bench (DTB) used for testing the output energy from ballistic extracorporeal shock wave therapeutic devices, the measurements with DTB were compared with the acoustic energy measured with a Laser Doppler Vibrometer (LDV) for a commercial ballistic ESWT device. It was shown that the mechanical energy detected with DTB had variability maintained within 5 % at the same output power setting and also had a linear correlation (adj. R2 = 0.991) with the acoustic energy measured with the LDV for the entire output power settings. Using the correlation between the two methods and the correlation on the acoustic energy measured in between air and water with the LDV, the DTB measurement can be used to estimate the energy flux density in water with an average error of 7.85 % for the entire output power settings of the ballistic shock wave generator considered in the experiment. DTB provides information limited to the output mechanical energy and therefore it is not suitable for testing the various acoustic output parameters required in IEC61846 and IEC63045. However, DTB that is simple in measurement principles and easy to use is expected for manufacturers and clinical users to monitor the performance of ballistic Extracorporeal Shock Wave Therapy (ESWT) devices.

Micro-Shockwave Measurement and Evaluation of Laser Shock Peening (레이저 쇼크 피닝의 마이크로 충격파 측정 및 평가)

  • Kim, Joo-Han;Lee, Woo-Ram;Kim, Teak-Gu;Cheong, Seong-Kyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.10
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    • pp.1041-1046
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    • 2011
  • Micro shockwaves are induced in laser shock peening and their effect on metal samples is presented. Laser shock peening produces maximized internal compressive stress on metal surfaces. This research evaluated the effects of micro shockwaves from laser shock peening with a pulsed Nd:YAG laser on steel samples, through the analysis of the mechanical properties of the samples. In the experiments, a piezo material was applied to measure the micro shockwaves and the hardnesses and micro tensile strengths of the samples were evaluated.

Control of Shock Wave/Boundary-Layer Interactions Using S-Shaped Mesoflaps (S-자형 플랩을 이용한 충격파와 경계층 간섭현상 제어에 관한 연구)

  • Lee Yeol
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.159-160
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    • 2002
  • New S-shaped aeroelastic mesoflaps are utilized to control normal shock/boundary-layer interactions. New generation of the mesoflaps is designed f3r a better rigidness and a good flow uniformity across the ulteractions. ,Major advantages of the mesoflap system can be a better total pressure recovery downstream of the interactions due to the lambda shock structure over the flap system, and a rehabilitation of the thickened boundary layer due to bleeding through a cavity underneath the flap system. Skin friction has been measured downstream of the interactions, using the laser interferometer skin friction (LISF) meter, which optically detects the rate of thinning of an oil film applied to the test surface. Various flap-thicknesses of the S-shaped mesoflap arrays are tested, and the results are compared to the solid-wall reference case. Overall, not much difference in the level of skin friction is noticed for the S-shaped flap arrays of various thicknesses, and its level is lower than the skin friction downstream of the solid-wall interaction

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Residual Stress Prediction in LSP Surface Treatment by Using FEM (유한요소법을 이용한 LSP 표면처리 공정의 잔류응력 예측)

  • Bang, Boo-Woon;Son, Seung-Kil;Kim, Jae-Min;Cho, Chong-Du
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.8
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    • pp.767-772
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    • 2009
  • Laser shock peening(LSP) is proving to be better surface treatment than conventional one such as shot peening. The LSP process has a compressive residual stress into a metal alloy and a significant improvement in fatigue life. Our research is focused on applying finite element method to the prediction of residual stress through the LSP processing in some LSP conditions such as pressure and spot size induced by laser. Two analysis methods are considered to calculating the compressive residual stress. But the explicit solution and the static one after partially explicit solving are almost same. In LSP, because of very high strain rate($10^6s^{-1}$), HEL(Hugoniot Elastic Limit) is the most important parameter in material behavior modeling. As the circular laser spot is considered, 2-D axisymmetric elements are used and the infinite elements are applied to boundaries for no reflection. The relations of material properties and the LSP are also important parts in this study.

Numerical simlation of nanosecond pulsed laser ablation in air (대기중 나노초 펄스레이저 어블레이션의 수치계산)

  • 오부국;김동식
    • Laser Solutions
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    • v.6 no.3
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    • pp.37-45
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    • 2003
  • Pulsed laser ablation is important in a variety of engineering applications involving precise removal of materials in laser micromachining and laser treatment of bio-materials. Particularly, detailed numerical simulation of complex laser ablation phenomena in air, taking the interaction between ablation plume and air into account, is required for many practical applications. In this paper, high-power pulsed laser ablation under atmospheric pressure is studied with emphasis on the vaporization model, especially recondensation ratio over the Knudsen layer. Furthermore, parametric studies are carried out to analyze the effect of laser fluence and background pressure on surface ablation and the dynamics of ablation plume. In the numerical calculation, the temperature, pressure, density, and vaporization flux on a solid substrate are obtained by a heat-transfer computation code based on the enthalpy method. The plume dynamics is calculated considering the effect of mass diffusion into the ambient air and plasma shielding. To verify the computation results, experiments for measuring the propagation of a laser induced shock wave are conducted as well.

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Nanoparticle Synthesis by Pulsed Laser Ablation of Consolidated Microparticles (압밀 금속 마이크로 입자의 펄스 레이저 ABLATION에 의한 나노입자 합성)

  • 장덕석;오부국;김동식
    • Laser Solutions
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    • v.5 no.2
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    • pp.31-38
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    • 2002
  • This paper describes the process of nanoparticle synthesis by laser ablation of consolidated microparticles. We have generated nanoparticles by high-power pulsed laser ablation of Al, Cu and Ag microparticles using a Q-switched Nd:YAG laser (wavelength 355 nm, FWHM 5 ㎱, fluence 0.8∼2.0 J/㎠). Microparticles of mean diameter 18∼80 ㎛ are ablated in the ambient air The generated nanoparticles are collected on a glass substrate and the size distribution and morphology are examined using a scanning electron microscope and a transmission electron microscope. The effect of laser fluence and collector position on the distribution of particle size is investigated. The dynamics of ablation plume and shock wave is analyzed by monitoring the photoacoustic probe-beam deflection signal. Nanosecond time-resolved images of the ablation process are also obtained by laser flash shadowgraphy. Based on the experimental results, discussions are made on the dynamics of ablation plume.

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Visualization of Plasma Produced in a Laser Beam and Gas Jet Interaction (레이저와 질소가스 상호충돌로부터 발생되는 플라스마 가시화)

  • Kim Jong-Uk;Kim Chang-Bum;Kim Guang-Hoon;Lee Hae-June;Suk Hy-Yong
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.39-42
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    • 2002
  • In the current study, characteristics of the laser-induced plasma were investigated in a gas filled chamber or in a gas jet by using a relatively low intensity laser $(I\;\leq\;5\;\times\;10^{12}\;W/cm^2)$. Temporal evolutions of the produced plasma were measured using the shadow visualization and the shock wave propagation as well as the electron density profiles in the plasma channel was measured using the Mach-Zehnder interferometry. Experimental results such as the structure of the produced plasma, shock propagation speed $(V_s)$, electron density profiles $(n_e)$, and the electron temperature $(T_e)$ are discussed in this study. Since the diagnostic laser pulse occurs over short time intervals compared to the hydrodynamic time scales of expanding plasma or a gas jet, all the transient motion occurring during the measurement is assumed to be essentially frozen. Therefore, temporally well-resolved quantitative measurements were possible in this study.

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Development of shock wave induced microparticle acceleration system based on laser ablation and its application on drug delivery (충격파를 이용한 레이저 어블레이션 기반의 마이크로 입자 가속 시스템 개발 및 약물전달 응용)

  • Choi, Ji-Hee;Gojani, Ardian B.;Lee, Hyun-Hee;Yoh, Jai-Ick
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.6
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    • pp.587-593
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    • 2008
  • Transdermal and topical drug delivery with minimal tissue damage has been an area of vigorous research for years. Our research team has initiated the development of an effective method for delivering drug particles across the skin (transdermal) for systemic circulation, and to localized (topical) areas. The device consists of a laser ablation based micro-particle acceleration system that can be integrated with endoscopic surgical techniques. We have successfully delivered 3μm size cobalt particles into gelatin models that represent soft tissue with remarkable penetration depth.