• Title/Summary/Keyword: wave separation

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Flow Regimes of Continuously Stratified Flow over a Double Mountain (두 개의 산악 위에서의 연속적으로 성층화된 흐름의 흐름 체계)

  • Han, Ji-Young;Kim, Jae-Jin;Baik, Jong-Jin
    • Atmosphere
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    • v.17 no.3
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    • pp.231-240
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    • 2007
  • The flow regimes of continuously stratified flow over a double mountain and the effects of a double mountain on wave breaking, upstream blocking, and severe downslope windstorms are investigated using a mesoscale numerical model (ARPS). According to the occurrence or non-occurrence of wave breaking and upstream blocking, three different flow regimes are identified over a double mountain. Higher critical Froude numbers are required for wave breaking and upstream blocking initiation for a double mountain than for an isolated mountain. This means that the nonlinearity and blocking effect for a double mountain is larger than that for an isolated mountain. As the separation distance between two mountains decreases, the degree of flow nonlinearity increases, while the blocking effect decreases. A rapid increase of the surface horizontal velocity downwind of each mountain near the critical mountain height for wave breaking initiation indicates that severe downslope windstorms are enhanced by wave breaking. For the flow with wave breaking, the numerically calculated surface drag is much larger than theoretically calculated one because the region with the maximum negative perturbation pressure moves from the top to the downwind slope of each mountain as the internal jump propagating downwind occurs.

Numerical Study of Shock Wave-Boundary Layer Interaction in a Curved Flow Path (굽어진 유로 내부의 충격파-경계층 상호작용 수치연구)

  • Kim, Jae-Eun;Jeong, Seung-Min;Choi, Jeong-Yeol;Hwang, Yoojun
    • Journal of the Korean Society of Propulsion Engineers
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    • v.25 no.6
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    • pp.36-44
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    • 2021
  • Numerical analysis was performed on the shock wave-boundary layer interaction generated in the internal flow path of the curved interstage of the scramjet engine flight test vehicle. For numerical analysis, the turbulence model k-ω SST was used in the compressibility Raynolds Averaged Navier Stokes(RANS) equation. Representatively, the separation bubbles on the upper wall of the nozzle, the interaction between the concave shock wave and the boundary layer, and the shock wave-shock wave interaction at the edge were captured. The analysis result visualizes the shock wave-boundary layer interaction of the curved internal flow path to enhance understanding and suggest design considerations.

A Parametric Study of Ridge-cut Explosive Bolts using Hydrocodes

  • Lee, Juho;Han, Jae-Hung;Lee, YeungJo;Lee, Hyoungjin
    • International Journal of Aeronautical and Space Sciences
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    • v.16 no.1
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    • pp.50-63
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    • 2015
  • Explosive bolts are one of pyrotechnic release devices, which are highly reliable and efficient for a built-in release. Among them, ridge-cut explosive bolts which utilize shock wave generated by detonation to separate bolt body produce minimal fragments, little swelling and clean breaks. In this study, separation phenomena of ridge-cut explosive bolts or ridge-cut mechanism are computationally analyzed using Hydrocodes. To analyze separation mechanism of ridge-cut explosive bolts, fluid-structure interactions with complex material modeling are essential. For modeling of high explosives (RDX and PETN), Euler elements with Jones-Wilkins-Lee E.O.S. are utilized. For Lagrange elements of bolt body structures, shock E.O.S., Johnson-Cook strength model, and principal stress failure criteria are used. From the computational analysis of the author's explosive bolt model, computational analysis framework is verified and perfected with tuned failure criteria. Practical design improvements are also suggested based on a parametric study. Some design parameters, such as explosive weights, ridge angle, and ridge position, are chosen that might affect the separation reliability; and analysis is carried out for several designs. The results of this study provide useful information to avoid unnecessary separation experiments related with design parameters.

Multicomponent RVSP Survey for Imaging Thin Layer Bearing Oil Sand (박층 오일샌드 영상화를 위한 다성분 역VSP 탐사)

  • Jeong, Soo-Cheol;Byun, Joong-Moo
    • Geophysics and Geophysical Exploration
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    • v.14 no.3
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    • pp.234-241
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    • 2011
  • Recently, exploration and development of oil sands are thriving due to high oil price. Because oil sands reservoir usually exists as a thin layer, multicomponent VSP, which has the advantage of the high-resolution around the borehole, is more effective than surface seismic survey in exploring oil sand reservoir. In addition, prestack phase-screen migration is effective for multicomponent seismic data because it is based on an one-way wave equation. In this study, we examined the applicability of the prestack phase-screen migration for multicomponent RVSP data to image the thin oil sand reservoir. As a preprocessing tool, we presented a method for separating P-wave and PS-wave from multicomponent RVSP data by using incidence angle and rotation matrix. To verify it, we have applied the developed wavefield separation method to synthetic data obtained from the velocity model including a horizontal layer and dipping layers. Also, we compared the migrated image by using P-wave with that by using PS-wave. As a result, the PS-wave migrated image has higher resolution and wide coverage than P-wave migrated image. Finally, we have applied the prestack phase-screen migration to the synthetic data from the velocity model simulating oil sand reservoir in Canada. The results show that the PS-wave migrated image describe the top and bottom boundaries of the thin oil sand reservoir more clearly than the P-wave migrated image.

Analysis of Ultrasonic Scattering from Side-drilled Holes (원주형 기공에 대한 초음파 산란 해석)

  • Jeong, Hyun-Jo;Park, Moon-Cheol
    • Journal of the Korean Society for Nondestructive Testing
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    • v.24 no.6
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    • pp.559-565
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    • 2004
  • Two different methods were used for the scattering analysis of side-drilled holes(SDH). The scattering models include an explicit model based on the Kirchhoff approximation and the solution of the exact separation of variables. The far-field scattering amplitude was calculated and their time-domain results were compared for the case of shear vertical wave. The exact solution predicts the existence of the creeping wave. The Kirchhoff approximation agreed to the exact solution, except the case of the creeping wave. Two measurement models were introduced to predict the response from the SDHs for the case of immersion, pulse-echo testing. The received voltage was calculated for the case of the shear vertical waves with the incident angle of $45^{\circ}$ to the SDH with the diameter of 1mm, and compared with the experimental results.

Mode Separation in Torsional Guided Waves Using Chirplet Transform (첩릿변환을 이용한 비틀림 유도파 모드분리)

  • Kim, Young-Wann;Park, Kyung-Jo
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.24 no.4
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    • pp.324-331
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    • 2014
  • The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet transform based on the maximum likelihood estimation, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. Simulation results on a carbon steel pipe are presented, which show the accurate mode separation and more discernible time-frequency representation could become enabled using the proposed technique.

Numerical Visualization of the Pseudo-Shock Waves using LES (LES를 이용한 Pseudo-Shock Waves의 가시화)

  • Deng, Ruoyu;Jin, Yingzi;Kim, Heuy Dong
    • Journal of the Korean Society of Visualization
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    • v.13 no.3
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    • pp.29-34
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    • 2015
  • The interaction between a normal shock wave and a boundary layer along a wall surface in internal compressible flows causes a very complicated flow. This interaction region containing shock train and mixing region is called as pseudo-shock waves. Pseudo-shock waves in the divergent part of a rectangular nozzle have been investigated by using large-eddy simulation (LES). LES studies have been done for the complex flow phenomena of three-dimensional pseudo-shock waves. The LES results have been validated against experimental wall-pressure measurements. The LES results are in good agreement with experimental results. Pseudo-shock length and corner separation have been studied in three-dimensional LES model. Comparison of centerline pressure measurement and 3D visualization measurement has been discussed for the corner separation position. It has been concluded that the pseudo-shock length should be measured by using 3D visualization measurement.

Unsteady Separation Characteristics of Air-Launching Rocket from Full-Geometry Mother Plane (초음속 공중발사를 위한 전기체-로켓의 비정상 분리 유동특성)

  • Ji, Young-Moo;Byun, Yung-Hwan;Park, Jun-Sang;Lee, Jae-Woo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.6
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    • pp.474-482
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    • 2007
  • An analysis is made for flow and rocket motion during a supersonic separation stage of an air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations are numerically solved to analyze the steady/unsteady flow fields around the rocket which is being separated from the mother plane configuration(F-4E Phantom). Simulation results clearly demonstrate the effect of shock-expansion wave interaction around both of the rocket and the mother plane. To predict the behavior of the ALR by the change of the center-of-gravity, three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rockets for safe separation is proposed.

Center-of-Gravity Effect on Supersonic Separation from the Mother Plane (무게중심 변화에 따른 초음속 공중발사 로켓의 모선분리 연구)

  • Ji Young-Moo;Lee Jae-Woo;Byun Yung-Hwan;Park Jun-Sang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2006.05a
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    • pp.36-40
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    • 2006
  • An analysis is made of flow and rocket motion during a supersonic separation stage of air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations is numerically solved to analyze the steady/unsteady flow field around the rocket which is being separated from the mother plane configuration(F-4E Phantom). The simulation results clearly demonstrate the effect of shock-expansion wave interaction between the rocket and the mother plane. To predict the behavior of the ALR according to the change of the C.G., three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rocket for the safe separation is proposed.

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Identification of Diametrical Node Number of Travelling Wave Modes is Rotating Disk-Use of Directional Frequency Response Function (회전원판의 진행파 모드 절직경 수 규명-방향성 주파수응답함수의 이용)

  • Kim, Myeong-Eop;Lee, Chong-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.3
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    • pp.960-967
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    • 1996
  • Directional frequency response functions(dFRFs) are introduced for isotropic rotating disks, treating pairs of excitations and measurements as the complex input and output, respectively. It is shown that the dFRFs can be effectively used for separation of the forward and backward travelling wave modes and identification of the diametrical node numbers associated with modes of interst. Numerical simuations and experimental works are performed to demonstrate the analytical development and its validity.