Effect of input signal type and time delay in sensors on wave velocity in rock specimens

Kim, Jin-Yeon,Jang, Jaewon,Yun, Tae Sup Elsevier 2019 Engineering Geology Vol.260 No.-

<P><B>Abstract</B></P> <P>Accurate determination of wave velocity is critical to evaluating small-strain stiffness and helps identify anisotropy in rocks. The time delay in transducers and the selection of input signal types influence the computed wave velocity. Four types of input signals are used to obtain the travel time by determining the first arrival time and computing the peak-to-peak time for granite and sandstone specimens, and the phase velocity is computed by subtracting the time delay occurring in transducers from the travel time. The results show that the first arrival time and the peak-to-peak time tend to overestimate and underestimate, respectively, the velocity and a tone-burst signal comprising a 5-cycle sine burst is most appropriate to gather the reliable velocity in laboratory-scale experiments. The estimation of anisotropy in granite and sandstone is well defined when a tone-burst signal is used. The accuracy of wave velocity measurement technique using first-propagated tone-burst signal is investigated by comparing the wave velocity measured by using reflected signals. The velocity measurement proposed by this study is useful to accurately estimated rock properties such as uniaxial compressive strength, poison ratio, elastic modulus, and shear modulus.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Investigation of unavoidable time delay in transducer for elastic wave velocity measurement. </LI> <LI> Prevalent effect of input signal types on measured wave velocity values. </LI> <LI> Robustness of tone-burst signal for characterizing the anisotropy in rocks. </LI> </UL> </P>

응력유도 및 고유 이방성에 따른 전단파 속도 특성

이창호,이종섭,윤형구,쭝훙꿍,조태현 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.11

Shear wave velocity of uncemented soil can be expressed as the function of effective stresses when capillary phenomena are negligible. However, the terms of effective stresses are divided into the direction of wave propagation and polarization because stress states are generally anisotropy. The shear wave velocities are affected by parameters and exponents that are experimentally determined. The exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the parameters are changed by contact behaviors among particles, material properties of particles, and type of packing (i.e., void ratio and coordination number). In this study, consolidation tests are performed by using clay, mica and sand specimens. Shear wave velocities are measured during consolidation tests to investigate the stress-induced and inherent anisotropies by using bender elements. Results show the shear wave velocity depends on the stress-induced anisotropy for round particles. Furthermore, the shear wave velocity is dependent on particle alignment under the constant effective stress. This study suggests that the shear wave velocity and the shear modulus should be carefully estimated and used for the design and construction of geotechnical structures.

수포화 및 가열건조 암석 코어의 시간 경과에 따른 탄성파 속도 이방성 분석 연구

이상규,이태종,고휘철,최지향 한국자원공학회 2011 한국자원공학회지 Vol.48 No.6

Laboratory seismic velocity measurements have been carried out for transversely isotopic core samples with respect to anisotropic angle and water contents for three different rock types; biotite gneiss, bitotite schist, and shale. A total of 21 rock samples were prepared by coring from a block of rock body with roughly 15 degree rotating from 0 to 90 degree for each rock types. Velocity has been monitored for an hour at room temperature starting from fully saturated condition and from dry condition. It showed highest seismic anisotropy in schist, and weakest in gneiss. Saturated condition shows bigger anisotropy coefficient than dry condition in P-wave velocity, while significant difference could not be observed in S-wave velocity. Water contents seems to yield much higher increase in P-wave velocity when the anisotropic angle is small, which the wave propagation direction is rather perpendicular to the foliation or bedding plane. The air in the pore space which is roughly aligned to the foliation direction can be considered to cause bigger difference in P-wave velocity than pore water. 흑운모편마암, 흑운모편암, 셰일의 세가지 암석에 대하여 이방성 각도를 달리하며 0-90도까지 15도 간격으로 7개씩 성형해서 만든 21개의 시험편을 이용하여 수포화 및 가열건조 시킨 후, 상온・상습 환경에서 1시간 동안 변화하는 탄성파 속도를 연속하여 측정하고 그 결과를 분석하였다. P-파의 이방성은 편암에서 가장 크고, 셰일, 흑운모편마암 순으로 나타났으며 시료가 수포화되어 있을 때 보다는 건조상태에서 이방성 계수가 크게 나타났다. 반면 S-파의 경우는 이방성 각도나 수포화 여부에 큰 영향을 받지 않는다. 함수율의 영향은 이방성 각도가 작아 파의 진행방향이 엽리 혹은 층리면과 수직에 가까운 경우에 더욱 크다. 이는 같은 형태와 분포를 갖는 공극을 공극수가 채우고 있을 때보다 공기가 채우고 있을수록 공극 혹은 절리의 영향이 크게 작용되어 속도 차가 커지기 때문으로 해석된다.

Shear Wave Velocity in Unconsolidated Marine Sediments of the Western Continental Margin, the East Sea

Kim, Gil-Young,Kim, Dae-Choul The Acoustical Society of Korea 2003 韓國音響學會誌 Vol.22 No.e4

Shear wave velocity was measured and grain size analysis was conducted on two core samples obtained in unconsolidated marine sediments of the western continental margin, the East Sea. A pulse transmission technique based on the Hamilton frame was used to measure shear wave velocity. Duomorph ceramic bender transducer-receiver elements were used to generate and detect shear waves in sediment samples. Time delay was calculated by changing the sample length from the transducer-receiver element. Time delay is 43.18 μs and shear wave velocity (22.49 m/s) is calculated from the slope of regression line. Shear wave velocities of station 1 and 2 range from 8.9 to 19.0 m/s and from 8.8 to 22 mis, respectively. Shear wave velocities with depth in both cores are qualitatively in agreement with the compared model〔1〕, although the absolute value is different. The sediment type of two core samples is mud (mean grain size, 8-9Φ). Shear wave velocity generally increases with sediment depth, which is suggesting normally consolidated sediments. The complicated variation of velocity anisotropy with depth at station 2 is probably responsible for sediment disturbance by possible gas effect.

비등방성을 고려한 사행하천의 유속 공간보간기법 개발

유호준,김동수 한국수자원학회 2017 한국수자원학회논문집 Vol.50 No.7

2차원 유속장(flow field)은 하천흐름의 특성을 이해하기 위한 중요한 수리학적 자료 중 하나로서, 수공구조물 위치선정 및 설계, 하천에서의 이송-확산 예측, 하천 의 수리학적 거동을 예측하기 위한 중요한 기본 자료로 사용된다. 지금까지 이러한 하천흐름 특성을 예측하기 위해 제한적인 현장조건과 적절한 계측방법, 계측기기 의 기술적 한계로 인해 현장실험 보다는 다양한 수치모형을 이용하여 왔다. 하지만 최근에는 계측기기의 발달로 과거보다 정확하고 정밀한 현장계측이 가능하여 졌 으며, 현장 계측자료의 질적이고 양적인 수요를 만족시키고 있다. 대표적으로 초음파도플러유속계(ADCPs; Acoustic Doppler Current Profilers)는 유량을 정확하 게 측정하는 것으로 유명하며, 2차원 뿐만 아니라 3차원 유속장 등 자세한 유속자료를 제공한다. 하지만 이러한 측정 능력에도 불구하고, ADCP를 활용한 유속 측정 은 주로 횡단면 측정을 기본으로 수행하기 때문에, 수치모형의 결과와 같이 높은 밀도의 유속장을 얻기 위해서 공간보간기법이 활용되고 있다. 하지만 만곡이 존재하 는 자연하천은 하도형상에 따라 유속이 지속적으로 변화하기 때문에 일반적인 공간보간기법을 적용하기 어렵다. 즉, 자연하천의 만곡에 따른 비등방성을 고려하지 않 는다면, 역거리가중법(IDW)과 크리깅(Kriging)과 같은 일반적인 공간보간기법으로는 잘못된 결과를 초래할 수 있다. 본 연구에서는 이러한 문제점을 해결하고자 만곡이 존재하는 사행하천을 대상으로 방향성을 고려하기 위한 곡선좌표계와 비등방성을 고려하기 위한 비등방적 참 조범위를 적용한 공간보간기법을 개발하였다. 본 연구에서 제시한 기법을 한국건설기술연구원 하천실험센터에 존재하는 3개의 사행수로가 포함된 실규모의 실험수 로를 대상으로 적용한 결과, 평균제곱근오차와 상관계수는 기존의 공간보간기법과 비교하여 각각 41.5% 감소, 40.0%가 증가하여 정확성과 상관성이 개선되었다. Understanding of the two-dimensional velocity field is crucial in terms of analyzing various hydrodynamic and fluvial processes in the riverine environments. Until recently, many numerical models have played major roles of providing such velocity field instead of in-situ flow measurements, because there were limitations in instruments and methodologies suitable for efficiently measuring in the broad range of river reaches. In the last decades, however, the advent of modernized instrumentations started to revolutionize the flow measurements. Among others, acoustic Doppler current profilers (ADCPs) became very promising especially for accurately assessing streamflow discharge, and they are also able to provide the detailed velocity field very efficiently. Thus it became possible to capture the velocity field only with field observations. Since most of ADCPs measurements have been mostly conducted in the cross-sectional lines despite their capabilities, it is still required to apply appropriate interpolation methods to obtain dense velocity field as likely as results from numerical simulations. However, anisotropic nature of the meandering river channel could have brought in the difficulties for applying simple spatial interpolation methods for handling dynamic flow velocity vector, since the flow direction continuously changes over the curvature of the channel shape. Without considering anisotropic characteristics in terms of the meandering, therefore, conventional interpolation methods such as IDW and Kriging possibly lead to erroneous results, when they dealt with velocity vectors in the meandering channel. Based on the consecutive ADCP cross-sectional measurements in the meandering river channel. For this purpose, the geographic coordinate with the measured ADCP velocity was converted from the conventional Cartesian coordinate (x, y) to a curvilinear coordinate (s, n). The results from application of A-VIM showed significant improvement in accuracy as much as 41.5% in RMSE.

이방성을 고려한 자동속도분석

권택현,변중무,설순지 한국자원공학회 2013 한국자원공학회지 Vol.50 No.1

최근에는 탄성파 반사법 탐사기술의 발달로 먼 거리 벌림(offset)을 이용한 자료취득이 많이 이루어지고 있다. 이때 횡적 등방성(VTI) 매질에서 획득한 자료에 일반적인 NMO 속도분석을 적용하여 NMO 보정을 수행 할 경우 먼 거리 벌림에서 탄성파 이벤트들이 위로 말려 올라가는 현상이 나타나며 이는 정확한 속도분석이 이루어지지 않았음을 나타낸다. 이 연구에서는 이방성을 고려한 NMO 속도분석을 수행함과 동시에 이방성을 나타내는 이방성 변수 를 추출하는 모듈을 개발하였다. 또한 자동으로 닮음(semblance) 상에서 최대 에너지 지점을 선발하여 속도분석을 수행할 수 있도록 하여 3차원 탐사 자료와 같이 방대한 양의 자료의 경우에도 효율적이고 빠르게 자료처리를 할 수 있도록 하였다. 이러한 자동선발을 이용한 속도분석에 있어서 닮음의 해상도는 매우 중요한 요소이므로 보다 높은 해상도의 닮음을 제공하는 BDS(Bootstrapped Differential Semblance)를 이용하였다. 그리고 이 연구에서 개발한 모듈을 검증하기 위해 합성탄성파 탐사자료 및 축소모형 실험 자료에 적용하였고 그 결과 NMO 속도분석의 가정에 부합하는 경사가 크지 않은 지층의 경우 실제 모델과 거의 유사한 속도와 이방성 변수 값들을 추출하였고 중합결과 또한 향상됨을 확인하였다. Data acquisition including long spread offsets is recently implemented due to the development of exploration techniques. If NMO correction was carried out through the conventional NMO velocity analysis to data acquired at Vertical Transversely Isotropic (VTI) media, the shape of the moveout called “hockey-stick” could frequently appear in the part of long spread offset. This indicates that the conventional NMO velocity analysis dose not provide correct results. Thus, in this study, an NMO velocity analysis module was developed not only considering anisotropy but also extracting an anisotropic parameter η. In addition, the developed module can process huge amount of data like 3D data efficiently and rapidly because it picks the maximum energy points on the semblances automatically. It is important to obtain high-resolution semblances in order to pick the maximum points accurately. Therefore, the developed module uses a bootstrapped differential semblance (BDS) instead of a conventional semblance to provide better resolution. To validate our developed module, it was applied to the numerical and the physical modeling data sets. The extracted velocities and anisotropic parameters were reasonable except in the case of deeply tilted layers, and stacked results were also improved.

The effect of anisotropy on wrinkling of tube under rotary draw bending

Kourosh Hasanpour,Mahmoud Barati,Behnaz Amini,Mehrdad Poursina 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.3

Rotary draw tube bending is one of the most complex tube forming processes subject to different process parameters such as mate-rial properties and geometry. This process is being practiced in more and more applications in industry due to its high efficiency, high forming precision and quality. However, improper process parameters can lead to wrinkling which restrict the thin walled tube bending. Therefore, the prediction and prevention of wrinkling is very important. Despite its importance, the effect of anisotropy on the occurrence of wrinkling was not considered in the literature up to now. In this investigation, a quantitative study on the wrinkling of thin walled tube bending is carried out through a finite element model of the process using velocity integral parameter, which is used for the detection of wrinkles. The other methods usually warn the wrinkling initiation with no precise location prediction. In addition, the effects of some process parameters, specially normal and planar anisotropy on the tube wrinkling are investigated. It is shown that increasing normal and planar anisotropy (increasing r0 and r90 values) result in a decrease in tube wrinkling.

대규모 발파자료를 이용한 한반도 남부 상부지각의 종파 속도 이방성

홍명호 ( Myung Ho Hong ),김기영 ( Ki Young Kim ) 한국지구물리·물리탐사학회 2009 지구물리와 물리탐사 Vol.12 No.3

속도 이방성 조사를 위한 다방위 역수직 탄성파 현장 실험

이두성 ( Doo Sung Lee ),김현규 ( Hyoun Gyu Kim ) 한국지구물리·물리탐사학회 1999 지구물리와 물리탐사 Vol.2 No.3

Torsional waves in fluid saturated porous layer clamped between two anisotropic media

Gupta, Shishir,Kundu, Santimoy,Pati, Prasenjit,Ahmed, Mostaid Techno-Press 2018 Geomechanics & engineering Vol.15 No.1

The paper aims to analyze the behaviour of torsional type surface waves propagating through fluid saturated inhomogeneous porous media clamped between two inhomogeneous anisotropic media. We considered three types of inhomogeneities in upper anisotropic layer which varies exponentially, quadratically and hyperbolically with depth. The anisotropic half space inhomogeneity varies linearly with depth and intermediate layer is taken as inhomogeneous fluid saturated porous media with sinusoidal variation. Following Biot, the dispersion equation has been derived in a closed form which contains Whittaker's function and its derivative, for approximate result that have been expanded asymptotically up to second term. Possible particular cases have been established which are in perfect agreement with standard results and observe that when one of the upper layer vanishes and other layer is homogeneous isotropic over a homogeneous half space, the velocity of torsional type surface waves coincides with that of classical Love type wave. Comparative study has been made to identify the effects of various dimensionless parameters viz. inhomogeneity parameters, anisotropy parameters, porosity parameter, and initial stress parameters on the torsional wave propagation by means of graphs using MATLAB. The study has its own relevance in connection with the propagation of seismic waves in the earth where fluid saturated poroelastic layer is present.