• Title/Summary/Keyword: Shock

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Morphological Transformation of Shock Waves Behind a Flat Plate

  • Chang, Se-Nyong;Lee, Soogab;Chang, Keun-Shik
    • Journal of Mechanical Science and Technology
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    • v.15 no.5
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    • pp.665-670
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    • 2001
  • The interaction of a travelling shock with the shear layer of a flat plate is studied computationally. The Euler and Navier-Stokes equations are solved numerically on quadrilateral unstructured adaptive grids. The flat plate is installed horizontally on the central axis of a shock tube. The shear layer is first created by two shock waves at different speeds splitted by a flat plate. A series of small vortices is developed as a consequence in the shear layer. The shock wave reflected at the end wall impinges the shear layer. The complicated shock dynamics in the evolution to the pseudo-steady state is represented with the morphological transformation of a planar shock into an oblique shock.

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Cures for Shock Instability: Development of an Improved Roe scheme (충격파 불안정성을 제거한 개선된 Roe 수치기법의 개발)

  • Kim Sung-soo;Kim Chongam;Rho Oh-Hyun;Hong Seung Kyu
    • 한국전산유체공학회:학술대회논문집
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    • 2001.05a
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    • pp.99-104
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    • 2001
  • This paper deals with the development of shock stable scheme that is free from shock instability. Roe's FDS is known to preserve good accuracy but to suffer from shock instability, i.e. the carbuncle phenomenon. As the first step toward the shock stable scheme, Roe's FDS is compared with HLLE scheme to identify the source of shock instability. Then control function f is introduced into the pressure term in Roe's FDS to cure shock instability. Various numerical tests concerned with shock instability are performed to demonstrate the shock stability of the proposed scheme.

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The Ultimate Pattern of Shock-Vortex Interaction

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.337-339
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    • 2008
  • As a shock impinges into a vortex of variable strength, complex shock diffraction can occur. Since a vortex has a fixed rotating direction, the shock wave travelling in one direction creates strong asymmetry in the vortex flow field. The process is that first the shock is divided into two parts by the vortex. One part is moving in the adverse direction opposite to the vortex flow which is captured by the vortex center. The other part is moving in the favorable direction, namely, in the direction same as the vortex flow; it is swung around the vortex, accelerating the vortex flow. In this paper we have investigated numerically using ENO scheme how and why the shock-vortex interaction patterns appear so different for different parametric values. Conclusion is that there are three different types of shock-vortex interaction depending on two related parameters: shock Mach number and vortex Mach number. We present a parameter map by which we can discern what type of interaction pattern appears as a shock impinges into a vortex.

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The Ultimate Pattern of Shock-Vortex Interaction

  • Chang, Keun-Shik;Barik, Hrushikesh;Chang, Se-Myong
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.337-339
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    • 2008
  • Abstract: As a shock impinges into a vortex of variable strength, complex shock diffraction can occur. Since a vortex has a fixed rotating direction, the shock wave travelling in one direction creates strong asymmetry in the vortex flow field. The process is that first the shock is divided into two parts by the vortex. One part is moving in the adverse direction opposite to the vortex flow which is captured by the vortex center. The other part is moving in the favorable direction, namely, in the direction same as the vortex flow; it is swung around the vortex, accelerating the vortex flow. In this paper we have investigated numerically using ENO scheme how and why the shock-vortex interaction patterns appear so different for different parametric values. Conclusion is that there are three different types of shock-vortex interaction depending on two related parameters: shock Mach number and vortex Mach number. We present a parameter map by which we can discern what type of interaction pattern appears as a shock impinges into a vortex.

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Reflected Wave and Transmitted Shock in the Shock-Vortex Interaction (충격파-와동 간섭에서 발생하는 반사파 및 관통 충격파)

  • Chang Se-Myong;Chang Keun-Shik;Lee Soogab
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.139-142
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    • 2002
  • An experimental model and a conceptual model are investigated in this paper with both shock tube experiment and numerical technique. The shock-vortex interaction generated by this model is visualized with various methods: holographic interferometry, shodowgraphy, and numerical computation. In terms of shock dynamics, there are two meaningful physics in the present problem. They are reflective wave from the slip layer at the vortex edge and transmitted shock penetrating the vortex core. The discussion in this study is mainly focused on the two kinds of waves contributing to the quadrupolar pressure distribution around the vortex center during the interaction.

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Investigation of acoustic monitoring on laser shock cleaning process (레이저 충격파 클리닝 공정에서 음향 모니터링에 관한 연구)

  • 김태훈;이종명;조성호;김도훈
    • Laser Solutions
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    • v.6 no.2
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    • pp.27-33
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    • 2003
  • A laser shock cleaning technology is a new dry cleaning methodology for the effective removal of small particles from the surface. This technique uses a plasma shock wave produced by a breakdown of air due to an intense laser pulse. In order to optimize the laser shock cleaning process, it needs to evaluate the cleaning performance quantitatively by using a monitoring technique. In this paper, an acoustic monitoring technique was attempted to investigate the laser shock cleaning process with an aim to optimize the cleaning process. A wide-band microphone with high sensitivity was utilized to detect acoustic signals during the cleaning process. It was found that the intensity of the shock wave was strongly dependent on the power density of laser beam and the gas species at the laser beam focus. As a power density was larger, the shock wave became stronger. It was also seen that the shock wave became stronger in the case of Ar gas compared with air and N$_2$ gas.

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Experimental analysis of flow field for laser shock wave cleaning (레이저 충격파 클리닝에서 발생되는 유동장의 실험적 해석)

  • 임현규;장덕석;김동식
    • Laser Solutions
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    • v.7 no.1
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    • pp.29-36
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    • 2004
  • The dynamics of laser-induced plasma/shock wave and the interaction with a surface in the laser shock cleaning process are analyzed by optical diagnostics. Shock wave is generated by a Q-switched Nd:YAG laser in air or with N$_2$, Ar, and He injection into the focal spot. The shock speed is measured by monitoring the photoacoustic probe-beam deflection signal under different conditions. In addition, nanosecond time-resolved images of shock wave propagation and interaction with the substrate are obtained by the laser-flash shadowgraphy. The results reveal the effect of various operation parameters of the laser shock cleaning process on shock wave intensity, energy-conversion efficiency, and flow characteristics. Discussions are made on the cleaning mechanisms based on the experimental observations.

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Weak Shock Waves Reflected from a Blunt Body (앞이 무딘 물체에서 반사되는 약한 충격파)

  • Chang, Se-Myong;Chang, Keun-Shik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.7
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    • pp.901-910
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    • 1999
  • Investigated In this paper is the shock reflection from a blunt body, In particular, a circular cylinder of 20 mm diameter, for the weak shock impinging in the range 1<$M_s$ <2. Pressure and shock speed are measured for various shock strengths. Double-pulse holographic interferograms are taken to study the unsteady flow field at $M_s=1.34$. These experimental results are, in overall, well compared with the unstructured adaptive finite volume computation of the Euler equations performed in this study. Correlation of incident and reflected shocks and shock-shock locus obtained by experiment, computation, and theory are presented in parallel.

Shock Test Facilities and their Application at KARI SITC (한국항공우주연구원의 충격시험설비 및 운용 현황)

  • 김홍배;이상설;문상무;우성현
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.11b
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    • pp.940-944
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    • 2001
  • Shock environments are generally classified two categories; One is mechanical shock environments encountered in handling, transportation, and service environments. The other is pyrotechnic shock (or pyroshock) environments generally initiated by firing of an ordnance item to separate or release a structural member of fastener. The objective of this paper is to present a set of shock test methods - specific characteristics induced by many shock test devices, test objects properties, and shock environments. In addition, it is introduced the application of shock test in Korean aerospace development program and others with shock test facilities of Korea Aerospace Research Institute.

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Shock Response Analysis of MIL-S-901D Floating Shock Platform (MIL-S-901D 부유식 충격시험기의 충격응답해석)

  • Kwon, Jeong-Il;Lee, Sang-Gab;Chung, Jung-Hoon
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.5 s.143
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    • pp.493-498
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    • 2005
  • Underwater explosion shock response analysis of a MIL-S-901D Standard Floating Shock Platform(SFSP) was performed using LS-DYNA/USA, and the accuracy of analysis results was examined through the comparison of them with the existing test results. Surrounding fluid as well as the SFSP was included In a three dimensional finite element model for the consideration of the cavitation effects of UNOEX shock wave. It was confirmed that the analysis results could predict accurately the shock behaviors of the SFSP, and the response characteristics according to heavy weight shock tests could be figured out well.