• 한국지반공학회논문집
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• 제35권2호
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• pp.29-36
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• 2019

본 연구에서는 필댐 사력부 전단파 속도 주상도 결정시 물성치 변동성에 의해 발생 가능한 불확실성을 평가하고, 평가된 불확실성이 반영된 국내 필댐 사력부를 위한 전단파 속도 주상도 모델을 제안하였다. 이를 위하여 평가된 불확실성을 바탕으로 국내 필댐 사력부에 존재 가능한 깊이-전단파 속도 곡선 400개를 결정하고, 이에 대한 통계분석을 통하여 깊이별 전단파 속도 상한과 하한 곡선을 결정하였다. 결정된 곡선을 바탕으로 Burger 모델 형태의 깊이별 전단파 속도 상한과 하한 주상도 모델을 결정하였다. 결정된 모델은 국내에서 많이 사용되고 있는 Sawada-Takahashi 모델과 비교하였다.

• 산업기술연구
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• 제27권A호
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• pp.9-14
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• 2007

This study was designated to clarify the aspect of the wave propagation around the cavity. The change of traveltime and amplitude of the seismic wave was observed according to the various wave velocities of the cavity. The seismic wave detour or penetrate the cavity depending on the seismic velocity of the in-filled material. Generally, seismic wave detours toward high velocity zone around the cavity, and when the velocity of the cavity material reaches to 80 % of the base rock, the wave penetrates the cavity. The traveltime of the detouring seismic wave is not sensitive to the change of the cavity velocity, but as the velocity of the cavity increases, the fall of the amplitude was reduced. The penetrating wave showed the steeply increasing amplitude due to the reiteration of the detouring wave.

• Journal of the Korean Wood Science and Technology
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• 제27권1호
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• pp.50-55
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• 1999

Since ultrasonic stress wave velocity varies with wood temperature and moisture content, ultrasonic stress wave could be a tool to predict wood moisture content if temperature effect could be eliminated. This temperature effect was investigated by measuring the velocities of ultrasonic stress waves transmitting through air, a metal bar and a dimension lumber at various temperatures. For air the velocity and amplitude of the ultrasonic stress wave increase with temperature, while for a metal bar and a dimension lumber those decrease as temperature increases. However all three materials showed velocity hystereses with a temperature cycle. The effect of temperature and moisture content on stress wave velocity of a dimension lumber was depicted in the form of a three dimensional graph. The plot of stress wave velocity vs. wood moisture content was well fitted by two regression equations: a exponential equation below 46% and a linear equation above 46%.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.725-730
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• 1998

Recently, non-destructive tests are getting popular in evaluating concrete properties without braking specimens. Among several NDT methods, P-wave velocity measurement technique has been widely used to evaluate the stiffness and strength of concrete. The purpose of this study is to investigate factors influencing P-wave velocity measured by impact-resonant method and ultrasonic pulse velocity method, such as moisture content of concrete, existence and size of coarse aggregates, sensor and sampling rate. Test results show that rod-wave velocity measured by impact-resonant method and ultrasonic pulse velocity are significantly affected by the moisture content of concrete, i.e., the lower moisture content, the lower velocity. Moisture content influences rod-wave velocity stronger than ultrasonic pulse velocity. Rod-wave velocity is faster in concrete than in mortar and is also faster in concrete containing small size aggregates. Sensor and sampling rate have little influence on velocity.

• Journal of Magnetics
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• 제20권1호
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• pp.47-51
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• 2015

We measured radial arterial pulse signals using a prototype of a clip-type pulsimeter equipped with a permanent magnet and a Hall device, which produced signals through a voltage-detecting circuit. The systolic peak time and the reflective peak time for a temporally pulsed signal were analyzed for an arbitrary pulse wave at one position of a small permanent magnet. The measured value of the peripheral pulse wave velocity was about 1.25-1.52 m/s, demonstrating the accuracy of this new method. To measure the peripheral blood flow velocity, we simultaneously connected the radial artery pulsimeter to a photoplethysmography meter. The average value of the peripheral blood flow velocity was about 0.27-0.50 m/s.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.318-326
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• 2008

Recently, a new seismic probe, called "MudFork", has been developed and can be utilized for accurate and easy measurements of shear wave velocities of soft soils. To expand its use to estimate undrained shear strength and density, correlations between those and shear wave velocity were being attempted. Cone penetration tests and a seismic test, using MudFork, were performed at a soft ground site near Incheon, Korea. Also, undisturbed samples were obtained and shear wave velocities of the samples were measured as well as undrained shear strength, using triaxial compression test and bender elements. A simple linear relationship between shear strength and shear wave velocity was obtained, and a tentative relationship between density and shear wave velocity was also defined.

• 보존과학연구
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• 통권31호
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• pp.31-42
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• 2010

This study were performed thermal shock test for four kind of different rocks (Iksan granite, Namsan granite, Jeongseon marble, Yeongyang sandstone), and according to heating temperature($400^{\circ}C$, $600^{\circ}C$) on samples were investigated physical properties such as specify gravity, porosity, p-wave velocity. As a result, the tendency was appeared that porosity increased, and specific gravity and p-wave velocity decreased at a more higher temperature. But, the situation of change appeared characteristic according to temperature and rock types. In the case of Yeongyang sandstone, it appeared in especially porosity increasing at $400^{\circ}C$. The specific gravity was little change in the all the rock at $400^{\circ}C$ but the decreased at $600^{\circ}C$. Therefore the specific gravity in the temperature range is due to the relatively small impact on the change is expected. Porosity of the granite at $400^{\circ}C$ changes little. but marble in the rate of change is large. Conversely, the sandstone porosity decreased. At $600^{\circ}C$ increased porosity in all of rocks. particularly sandstone the smallest increase in porosity. Experiments showed that p-wave velocity measured through dry rocks was sensitive to quantify the thermal damage. The p-wave velocity of all rocks decreased with increasing temperature. In the relation between porosity and p-wave velocity, p-wave velocity decreased with increasing porosity. On the other hand, in case of Yeongyang sandstone p-wave velocity decreased with decreasing porosity. thus, development of microcracks more affects p-wave velocity than porosity. In this study, damage intensity was well explained with porosity and p-wave velocity values depending on temperature increase.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.544-550
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• 1997

In this study, the advanced on-sided stress wave velocity measurement method was applied to investigate the effects of composition, age and moisture content in concrete. Two concrete specimens that have different composition were used to figure out the change of the Longitudinal and Surface wave velocity due to different composition. The other concrete specimen was cast and the Longitudinal and Surface wave velocity was monitored during curing process. After 28-day old, the effect of moisture content in the concrete specimen to the stress wave velocity is presented in this paper during the time period 43-74 days after casting. For drying process. an aggregate drying oven was used. A conventional ultrasonic through transmission method was used to compare with the results determined by the one-sided method.

• Smart Structures and Systems
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• 제7권4호
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• pp.289-302
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• 2011

In marine clay deposits, naturally formed or artificially reclaimed, the evaluation and monitoring of the consolidation process has been a critical issue in civil engineering practices due to the time frame required for completing the consolidation process, which range from several days to several years. While complementing the conventional iconographic method suggested by Casagrande and recently developed in-situ techniques that measure the shear wave, this study suggests an alternative experimental procedure that can be used to evaluate the consolidation state of marine clay deposits using the shear wave velocity. A laboratory consolidation testing apparatus was implemented with bimorph-type piezoelectric bender elements to determine the effective stress-shear wave velocity (${\sigma}^{\prime}-V_s$) relationship with the marine clays of interest. The in-situ consolidation state was then evaluated by comparing the in-situ shear wave velocity data with the effective stress-shear wave velocity relationships obtained from laboratory experiments. The suggested methodology was applied and verified at three different sites in South Korea, i.e., a foreshore site in Incheon, a submarine deposit in Busan, and an estuary delta deposit in Busan. It is found that the shear wave-based experimental procedure presented in this paper can be effectively and reliably used to evaluate the consolidation state of marine clay deposits.

• The Journal of the Acoustical Society of Korea
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• 제26권1E호
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• pp.33-38
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• 2007

Compressional wave velocity and shear wave velocity were measured for gassy sediments collected from Jinhae Bay, Korea. To distinguish inhomogeneities of gassy sediments, Computed Tomography (CT) was carried out for gassy sediment using CT Scanner. The cored sediments are composed of homogeneous and soft mud (greater than $8{\Phi}$ in mean grain size) containing clay content more than 50%. In depth interval of gassy sediments, compressional wave velocity is significantly decreased from 1480m/s to 1360m/s, indicating that the gas greatly affects compressional wave velocity due to a gas and/or degassing cracks. Shear wave velocity shows a slight increasing pattern from ${\sim}55\;m/s$ in the upper part of the core to ${\sim}58\;m/s$ at 320 cm depth, and then decreases to ${\sim}54\;m/s$ in the lower part of the core containing a small amount of gas. But shear wave velocity in the gassy sediments is slightly greater than that of non-gassy sediments in the upper part of the core. Thus, the Vp/Vs ratio is decreased (from 30 to 25) in gas charged zone. The Vp/Vs ratio is well correlated with shear wave velocity, but no correlation with compressional wave velocity. This suggests that low concentrations of gas have little affects on shear wave velocity. By CT images, the gas in the sediments is mostly concentrated around inner edge of core liner due to a long duration after sediment collection.