• Title, Summary, Keyword: 압축파

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An Experimental Investigation of the Variations of the Elastic Wave Velocities with Compaction Energy for Railway Roadbed Materials (다짐 에너지를 고려한 노반 성토 재료의 탄성파 속도 변화의 실험적 분석)

  • Kim, Hak-Sung;Jung, Young-Hoon;Mok, Young-Jin;Lee, Jin-Wook
    • Journal of The Korean Society of Civil Engineers
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    • v.33 no.3
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    • pp.1037-1047
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    • 2013
  • A systematic laboratory compaction testing was performed with the laboratory seismic measurements of the compacted specimens sampled from various compaction fills and was supplemented with in-situ seismic testing to investigate the effects of compaction energy on the elastic wave velocities of the railway roadbed materials. The both variances of the compressive and shear wave velocities with moisture content curve ($V_p$-w and $V_s$-w curves) are similar to the general trend of the density-moisture content curve(${\gamma}_d$-w curve). At the wet side of optimal moisture content (OMC), either $V_p$ or $V_s$ does not significantly increase, which is well reflecting the no gaining in density with the increasing compaction energy exceeding modified-D compaction effort. $V_p$ increases linearly with ${\gamma}_d$ at the dry side of OMC, while it does exponentially at the wet side. The in-situ wave velocities were found to be influenced by the level of confinement and $V_s$ was more sensitive to compaction energy than $V_p$.

Development of Torsional Shear Testing System to Measure P-wave Velocity, S-wave Velocity and Pore Water Pressure Buildup on Fully and Partially Saturated Sands (포화 및 부분 포화 사질토의 Vp와 Vs 속도 및 과잉간극수압 측정을 위한 비틂전단 시험기의 개발)

  • Kim, Dong-Soo;Lee, Sei-Hyun;Choo, Yun-Wook
    • Journal of the Korean Geoenvironmental Society
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    • v.7 no.1
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    • pp.55-66
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    • 2006
  • Laboratory tests have revealed that the liquefaction resistance of sands depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The velocity of compression waves(i.e. P-waves), which have been known to be influenced largely by the degree of saturation and can be measured conveniently in the field, appears as an indicator of saturation. In this paper, the Stokoe type torsional shear(TS) testing equipment is modified to saturate the specimen and measure the velocities of P-wave and S-wave and pore pressure buildup. The velocities of P-wave and S-wave for Toyoura sand from Japan is measured and compared at the various B-value (degree of saturation) which are partially saturated to fully saturated conditions. Additionally, the variation of the pore water pressure induced during undrained TS tests at the various B-value is measured and analyzed.

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Study on Correlation between Compressive Strength and Compressional Wave Velocity for CLSM According to Curing Time (양생시간에 따른 CLSM의 압축강도 및 압축파 속도 상관성 연구)

  • Han, Woojin;Lee, Jongsub;Cho, Samdeok;Kim, Jinhwan;Byun, Yonghoon
    • Journal of the Korean Geoenvironmental Society
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    • v.16 no.11
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    • pp.5-11
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    • 2015
  • The development of Controlled Low Strength Material (CLSM), which is a highly flowable material, has been performed for the application of backfill. The objective of this study is to compare the compressive strength and compressive wave velocity of CLSM according to the curing time. To investigate the characteristics of the CLSM consisting of sand, silt, water, flyash, and CSA cement, uniaxial compression test and flow test were carried out. For the measurement of compressional waves, a cell and a couple of transducers were used. The test results show that the compressive strength increases with the curing time, while the increment of compressive strength decreases with the curing time. In addition, the compressive wave velocity increases with the curing time, and the correlation between the compressive wave velocity and compressive strength is similar to exponential function. This study suggests that the correlation between the compressive wave velocity and compressive strength may be effectively used for the estimation of compressive strength of the CLSM at early curing time.

Wave Phenomenonin High-Speed Railway Tunnel (고속철도 터널에서 발생하는 유체역학적 파동현상)

  • 김희동
    • Journal of the KSME
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    • v.34 no.10
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    • pp.796-807
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    • 1994
  • 이 글에서는 고속철도 터널에서 열차에 의해 발생하는 압축파의 특성과 그의 전파거동에 관하여 기술하였다. 또 터널내에서 발생한 압축파가 터널 출구에서 충격음(미기압파)으로 방출되어 주 변의 환경에 큰 영향을 미치고 있다는 문제점을 지적하였으며, 이러한 소음의 발생 메카니즘과 소음의 저감 및 제어방법에 대하여 개괄적으로 기술하였다.

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Experimental Study on the Slanted Portals for Reducing the Micro-pressure Waves in High-speed Train-tunnel System(I) (고속철도 터널에서 경사갱구 입구의 미기압파 저감성능에 관한 연구(I))

  • Kim, Dong-Hyeon;Shin, Min-Ho;Han, Myeong Sik
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.2 no.2
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    • pp.3-10
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    • 2000
  • The compression wave produced when a high-speed train enters a tunnel propagates along the tunnel ahead of the train. The micro pressure wave related to the compression wave is a special physics phenomena created by high-speed train-tunnel interfaces. A among methods for the purpose of reducing the micro pressure wave is to delay the gradient of the compression wave by using aerodynamic structures. The objective of this paper is to determine the optimum slanted portal using the moving model rig. According to the results, the maximum value of micro pressure wave is reduced by 19.2% for the $45^{\circ}$ slanted portal installed at the entrance of the tunnel and reduced by 41.9% for the $45^{\circ}$ slanted portals at the entrance and exit of the tunnel. Also it is reduced by 34.6% for the $30^{\circ}$ slanted portals installed at the entrance and exit of the tunnel.

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Elastic Wave Characteristics According to Cementation of Dissolved Salt (용해된 소금의 고결화에 따른 탄성파 특성)

  • Eom, Yong-Hun;Truong, Q. Hung;Byun, Yong-Hoon;Lee, Jong-Sub
    • Journal of the Korean Geotechnical Society
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    • v.25 no.5
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    • pp.75-86
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    • 2009
  • Salt, one of the most common soluble materials in engineering soil, may have an effect on mechanical behaviors of soils under its cementation process. In order to investigate this natural phenomenon, non-soluble material by using glass beads is mixed with salt electrolyte and cemented by using oven to evaporate water. Three different sizes of glass bead particles, 0.26, 0.5, and 1.29 mm, with different salt concentration, 0, 0.1, 0.2, 0.5, 1.0, and 2.0M, are explored by using P- and S-waves, excited by bender elements and piezo disk elemets, respectively. The velocities of the P-wave and S-wave of the particulate medium cemented by salt show three stages with the degree of saturation: 1) S-wave velocities increase while P-wave velocities reduce with degree of saturation changing from 100% to 90%; 2) Both velocities are stable with degree of saturation varying from 90% to 10%; 3) The velocities change enormously when the specimens are nearly dry with degree of saturation from 10% to 0%. Besides, the resonance frequencies of S-wave show similar stages to the S-wave velocities. This study demonstrates meaningful trends of elastic wave characteristics of geo-materials according to the cementation of dissolved salt.

EDISON_CFD를 이용한 초음속 이중압축램프에서 난류 모델에 따른 유동현상 비교

  • Sin, Ho-Cheol
    • Proceeding of EDISON Challenge
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    • pp.585-589
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    • 2015
  • 본 연구에서는 이중압축램프의 초음속 유동에서 발생하는 충격파 경계층 상호작용을 EDISON_CFD로 해석하기로 한다. 이중압축램프에선 역압력 구배로 인하여 경계층이 박리가 일어나게 되고 박리된 경계층이 다시 이중압축램프에 부착되어 생겨난 박리영역을 관찰할 수 있다. 박리영역의 앞뒤로 유동의 방향이 바뀌게 되면서 압축 팬(compression fan)과 재부착 팬(reattachment fan)이 충격파를 발생시키고 이중압축램프전방의 충격파와 만나서 복잡한 유동 구조를 가지게 됨을 확인하였다. 이와 같은 층류에서 난류, 박리와 재부착의 영역에서의 해석하기 위해선 해석자의 난류모델이 중요하다. $15^{\circ}-30^{\circ}$, $15^{\circ}-45^{\circ}$의 두 종류의 이중압축램프를 $k-{\omega}$ SST 난류 모델과 ${\gamma}-Re_{\theta}$ 천이 모델로 계산을 EDISON_CFD로 수행하였다. 난류 모델의 차이를 표면마찰계수, 압력계수, 마하수로 비교하여 차이점을 분석하였다.

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Variation in Characteristics of Elastic Waves in Frozen Soils According to Degree of Saturation (포화도에 따른 동결토의 탄성파 특성 변화)

  • Park, Jung-Hee;Kang, Min-Gu;Lee, Jong-Sub
    • Journal of The Korean Society of Civil Engineers
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    • v.33 no.3
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    • pp.1063-1075
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    • 2013
  • The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the degree of saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the degree of saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from $20^{\circ}C$ to $-10^{\circ}C$, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the degree of saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of $0^{\circ}C$. This study renders the basic information of elastic waves in frozen soils according the degree of saturation.

A Methodology for Quality Control of Railroad Trackbed Fills Using Compressional Wave Velocities : II. Verification of Applicability (압축파 속도를 이용한 철도 토공노반의 품질관리 방안 : II. 적용성 검증)

  • Park, Chul-Soo;Mok, Young-Jin;Hwang, Seon-Keun;Park, In-Beom
    • Journal of the Korean Geotechnical Society
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    • v.25 no.9
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    • pp.57-66
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    • 2009
  • In the preliminary investigation (Park et al., 2009), the use of compressional wave velocity and its measurement techniques were proposed as a new quality control measure for trackbed fills. The methodology follows exactly the same procedure as the density control, except the density being replaced by the compressional wave velocity involving consistently with resilient modulus of design stage. The specifications for the control also include field compaction water content of optimum moisture content ${\pm}2%$ as well as the compressional wave velocity. In this sequel paper, crosshole and resonant column tests were performed as well direct-arrival method and laboratory compressional wave measurements to verify the practical applicability of a methodology far the new quality control procedure based upon compressional wave velocity. The stress-modified crosshole results reasonably well agree with the direct-arrival values, and the resonant column test results also agree well with the field crosshole results. The compressional wave velocity turned out to be an excellent control measure for trackbed fills both in the theoretical and practical point of view.

Shock Wave phenomena in Fluid enguneerung(II) (유체공학에서 충격파현상(2))

  • 김희동
    • Journal of the KSME
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    • v.35 no.1
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    • pp.71-83
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    • 1995
  • 최근 충격파현상을 이용하여 고온 고압의 상태를 용이하게 발생시킬 수 있는 기술 및 장치들이 여러 분야에서 요구되고 있으며, 이들에 대한 연구의 필요성이 갈수록 증대되어 가고 있다. 그 러나 우리나라에서의 충격파현상에 대한 이해와 지식은 비압축성 유체공학에 대한 연구에 비해 매우 미비한 실정이며, 이에 대한 관ㅅ미과 체계적인 연구가 절실한 실정이다. 일반적으로 충 격파현상을 이해하는 데에는 압축성 비정상흐름, 혹은 정상적인 초음속흐름에 대한 지식이 필 요하지만, 이 글에서는 충격파현상에 대한 이론적 기술들을 생략하고, 충격파현상들을 소개하기 위한 목적으로 충격파현상에 대한 현재의 연구동향과 충격파현상을 응용하는 실례들에 관해 간략히 기술하고, 충격파현상의 연구를 위해 필요한 충격과 발생장치에 대해서 기술하였다.

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