• Title/Summary/Keyword: Edge 음

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Numerical Analysis of Flow-Induced Noise by Vortex-Edge Interaction (Vortex-Edge의 상호작용에 기인한 유동소음의 전산해석)

  • KANG HO-KEUN;KIM EUN-RA
    • Journal of Ocean Engineering and Technology
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    • v.18 no.5
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    • pp.15-21
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    • 2004
  • An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.

Numerical Investigation of Aerodynamic Sounds by Vortex-Edge Interaction (Vortex-Edge 의 상호작용에 의한 유동소음의 수치계산)

  • Kang, Ho-Keun;Kim, Jeong-Hwan;Kim, Yu-Taek;Lee, Young-Ho
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1915-1920
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    • 2004
  • An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

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Direct Simulation of Edge Tones by the Finite Difference Lattice Boltzmann Method (차분격자볼츠만법에 의한 Edge음의 직접계산)

  • Kang, Ho-Keun;Kim, Yu-Taek;Lee, Young-Ho
    • 유체기계공업학회:학술대회논문집
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    • 2003.12a
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    • pp.671-677
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    • 2003
  • Two-dimensional direct numerical simulation of the edge-tones by the finite difference lattice Boltzmann method (FDLBM) is presented. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. It is clarified that the sound wave generated in rather wide region and individual vortices do not affect the sound wave propagation.

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An Analysis of Cutting Force in Micromachining (미소절삭에서의 절삭력 해석)

  • Kim, Dong Sik;Kahng, C.H.;Kwak, Yoon Keun
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.12
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    • pp.72-80
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    • 1995
  • Ultraprecision machining technology has been playing a rapidly increasing and important role in manufacturing. However, the physics of the micromachining process at very small depth of cut, which is typically 1 .mu. m or less is not well understool. Shear along the shear plane and friction at the rake face dominate in conventional machining range. But sliding along the flank face of the tool due to the elastic recovery of the workpiece material and the effects of plowing due to the large effective negative rake angle resultant from the tool edge radius may become important in micromachining range. This paper suggests an orthogonal cutting model considering the cutting edge radius and then quantifies the effect of plowing due to the large effective negative rake angle.

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Simulation of Trailing Edge Scattering Using Linearized Euler Equations with Source terms (CFD/CAA Hybrid 기법을 이용한 뒷전에서 음향파의 산란모사)

  • Park, Yong-Hwan;Bin, Jong-Hoon;Cheong, Cheol-Ung;Lee, Soo-Gab
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.7
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    • pp.18-25
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    • 2005
  • In this study, the main focus is the simulation of acoustic wave scattering in trailing edge and the analysis of the generation mechanism of instability wave by the interaction of trailing edge, shear flow and initial disturbance. The numerical algorithm is based on CFD/CAA hybrid method with high-order computational aeroacoustic method. It is found that steady mean flow gradient terms play a crucial role on the generation of instability wave through the comparison of simulations of Simple Linearized Euler Equation and Full Linearized Euler Equation. Through the comparison with the results of Full Navier-Stokes Equation, it is reasonable and efficient to use the Full Linearized Euler Equation in the initial generation mechanism of the instability wave near the trailing edge.

An Experimental Study on the Frequency Characteristics of Hole Tones Generated by a Circular Jet of Low Speed Impinging on a Plate with a Round Hole (저속의 원형분류가 구멍에 충돌할 때 발생한 구멍음의 주파수특성에 관한 실험적 연구)

  • 이동훈
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.6 no.2
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    • pp.34-41
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    • 1997
  • The objective of this study is to investigate experimentally the frequency characteristics of the hole tones generated by a circular jet of low speed impinging on a plate with a round hole. The experimental results about the sound spectrum and the time wave of the hole tone are presented and discussed in relation with the hole type, the jet velocity and the distance of the nozzle-to-plate with a round hole. From the sound spectrum and time wave measurements, it is found that the hole tone is generated not only by an interaction of convected vortices with a round hole but also by a series of vortex shedding from jets passing through a hole. The hole tones generated by a feedback mechanism consist of many frequency stages and also have a hysteresis phenomenon like an edge tone. But the hole tones generated by a series of vortex shedding have nothing with the stage characteristics. The frequencies of hole tones are influenced by the jet velocity, the distance of the nozzle-to-plate with a round hole and the hole type.

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Phase criterion of the feedback cycle of edgetones (쐐기소리의 되먹임 사이클의 위상조건)

  • Gwon, Yeong-Pil
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.3
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    • pp.1106-1113
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    • 1996
  • The phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet-edge interaction model which is based on the substitution of an array of dipoles for the reaction of the wedge to the impinging jet. The edgetone is produced by the feedback loop between the downstream-convected sinuous disturbance and upstream-propagating waves generated by the impingement of the disturbance on the wedge. By estimation of the phase difference between the downstream and the upstream disturbances, the relationship between the edge distance and the wavelength is obtained according to the phase-locking condition at the nozzle lip. With a little variation depending on the characteristics of jet-edge interaction, the criterion can be approximated as follows: h/.LAMBDA. + h/.lambda. = n - 1/4, where h is the stand-off distance between the nozzle lip and the edge tip, .LAMBDA. is the wavelength of downstream-convected wave, .lambda. is the wavelength of the upstream-propagating acoustic wave and n is the stage number for the ladder-like characteristics of frequency. The present criterion has been confirmed by estimating wavelengths from available experimental data and investigating their appropriateness. The above criterion has been found to be effective up to 90.deg. of wedge angle corresponding to the cavitytones.

Heavy-weight Floor Impact Sound Characteristics of Standard Laboratory by Slab Thickness (슬래브 두께에 따른 표준실험동의 중량충격음 특성)

  • Jeong, Young;Song, Hee-Soo;Jeon, Jin-Yong;Kim, Jin-Soo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.11a
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    • pp.103-108
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    • 2004
  • In this study, examined heavy-weight floor impact sound to structure that have slab thickness of 4 form at a standard laboratory through noise and vibration measured. The results show that the nature Natural frequency increased according to change of thickness of each slab by finite element analysis, and acceleration value decreased. Results of measurements of noise and vibration at a standard laboratory, the slab 210, 240mm structures was construed result such as finite element analysis but the slab 150, 180mm structures is construed that influence in vibration acceleration level because edge condition has condition that contact to ground. Therefore, in modelling process for analysis, is thought that need that condition analyzes examining element influencing about structure that contact to ground.

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Measurement System for Performance Evaluation of Acoustic Materials in a Small Water Tank (소형수조에서 음향재료의 반향음감소와 투과손실 측정시스템 구성)

  • Shin, Mi-Ru;Cho, Jung-Hong;Lee, Kyung-Teak;Kim, Jea-Soo;Jeon, Jae-Jin;Ham, Il-Bea;Kang, Chang-Gi
    • The Journal of the Acoustical Society of Korea
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    • v.30 no.2
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    • pp.63-72
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    • 2011
  • Since the detection probability is critically dependent on the target strength (TS) in active sonar and on the radiated noise level (RNL) in passive sonar, the acoustic materials for echo reduction (ER) and transmission loss (TL) are widely used for the stealth of underwater targets. In this paper, a measurement system based on the small water tank, for the frequency range of greater than 30 kHz, is developed and verified using reference targets. In order to design the water tank and the geometry of test samples, a program is developed to calculate the arrival time of interfering signals due to the reflection from water tank walls and also due to the diffraction from the edge of the test samples. Considering all the interfering signals, an optimal experimental configuration for water tank and test samples is designed and used throughout the experiment. Next, the signal processing algorithms to estimate ER and TL are developed based on the measured propagation loss reflecting the geometric spreading characteristics of the transducer. Finally, a set of reference targets such as aluminium plate and perfectly reflecting plate are used in a small water tank to verify the developed measurement system.

Finite Element Analysis on Negative Clearance Blanking of AL6061-T6 Foil (음의 클리어런스를 갖는 AL6061-T6 포일 블랭킹의 유한요소해석)

  • Song, Shin-Hyung;Choi, Woo Chun
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.25 no.4
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    • pp.290-294
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    • 2016
  • A finite element method (FEM) study was performed on micro-scale blanking of an AL6061-T6 foil with negative clearance. ABAQUS/explicit was used to prepare a simulation model of negative clearance blanking with tools having an edge radius comparable to the foil thickness. The Johnson-Cook plastic flow model was used in the simulations for the material flow. The FEM model was used to study the effects of various blanking parameters on the negative clearance blanking process and quality of the blank. In particular, the projecting edge on the bottom of the blank was observed. Research on negative blanking at the micro-scale is summarized and discussed.