• Composites Research
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• v.34 no.5
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• pp.330-336
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• 2021

Alumina powder is one of the widely used materials for industry, but there is a problem that the strength of the product changes depending on the powder packing state. To solve the above problem, previous studies have been conducted to increase the particle packing efficiency, but most of the existing studies analyzed the packing characteristics of millimeter-scale particles, so the physical properties are different from those of the micrometer scale. It is difficult to apply to the micrometer scale. In this paper, a three-step experiment was performed using a statistical method to increase packing using micrometer-scale alumina powder. First, a size combination with high packing and a mixing ratio were selected using the mixture test design method, and an appropriate excitation frequency was selected by analyzing the height change according to the frequency change in the vibration test apparatus. Finally, an alumina powder packing experiment was performed based on the experimental results mentioned above. As a result, it was confirmed that the maximum height variation was 42% higher than the maximum value of the 155 measurements performed when selecting the packing size combination. It is thought that this study will serve as basic data for processing and packing research using fine powder.

• Geophysics and Geophysical Exploration
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• v.22 no.2
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• pp.49-55
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• 2019

In this study, we presented a reference-shot subset method for stable convergence of full waveform inversion using a cyclic-shot subsampling technique. Full waveform inversion needs repetitive modeling of wave propagation and thus its calculation time increases as the number of sources increases. In order to reduce the computation time, we can use a cyclic-shot subsampling method; however, it makes the cost function oscillate in the early stage of the inversion and causes a problem in applying the convergence criteria. We introduced a method in which the cost function is calculated using a fixed reference-shot subset while updating the model parameters using the cyclic-shot subsampling method. Through the examples of full waveform inversion using the Marmousi velocity model, we confirmed that the convergence of cost function becomes stable even under the cyclic-shot subsampling method if using a reference-shot subset.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.287-294
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• 2021

In this study, tests were performed to analyze the feasibility of using the ground stabilizer from recycled resources such as blast furnace slag powder as filling material of prebored piles. For this, specimens were prepared by applying 70% and 83% of the general water/binder ratio of the filling material of prebored piles. And compression test, model test, and shaking table test were performed to determine the compressive strength, skin friction on the surface between prebored pile and filling material, and seismic performance of ground stabilizer. As a result of the tests, the compressive strength exceeded the relevant domestic standards, and the skin friction was equivalent to that of ordinary portland cement. In addition, the amount of vertical and horizontal displacement caused by earthquakes was found to be much smaller than the domestic standard. Therefore, when considering the test results comprehensively, it is judged that the feasibility of using a ground stabilizer from recycled resources as filling material for prebored pile is sufficient.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.103-103
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• 2016

최근 기후변화에 따른 집중호우로 도시홍수의 피해가 급격히 증가하고 있다. 특히 인구가 밀집하고 교통량이 많은 대도시의 경우 동일한 호우에 대하여 녹지나 농경지 등에 비해 그 피해가 더 심각하다. 일반적으로 홍수 피해의 직접원인은 외수로 인한 피해와 내수로 인한 피해로 크게 구분할 수 있다. 외수피해는 주로 소하천 및 지천의 범람, 제방의 붕괴 등으로 발생한 것이며 내수피해는 배수로, 하수도 및 펌프장의 내수배제능력 부족이 주된 원인이다. 따라서 도시홍수를 효과적으로 방어하기 위해서는 우선적으로 내배수시설의 성능개선이 선행되어야 할 필요가 있다. 이러한 내배수 시설의 성능 개선을 위해서는 현재 기 설치되어 있는 빗물펌프장의 설계 및 내배수 효율에 대한 성능평가가 필요하다. 하지만 현재 국내 펌프설계기준에는 빗물펌프장의 설계 및 운영에 대한 구체적인 성능 평가 방법이 제시되어 있지 않은 실정이다. 만약, 펌프 흡입수조 및 흡입파이프의 형상이 적절하게 설계되지 못한다면 물이 파이프 입구로 부드럽게 흡입되지 못하고 볼텍스 및 스월이 발생하게 된다. 이러한 볼텍스 및 스월은 펌프 입구 쪽으로 물 뿐 아니라 공기를 함께 흡입시킴으로써 펌프의 효율저하, 소음, 진동을 발생시키며 펌프 파손의 원인이 될 수 있다. 따라서 펌프를 설치하기 전 펌프 설치 후에 발생되는 펌프 흡입부 주변의 흐름특성 변화 및 흐름특성이 구조물에 미치는 영향 등을 고려하기 위하여 수리모형실험이 필요한데, 수리모형실험은 많은 시간과 비용이 들어가기 때문에 이를 대체할 수 있는 방안이 요구된다. 그런 이유로 최근에는 수리모형실험 대신 수치모의를 이용하는 경우가 많다. 수치모의의 결과는 수리실험의 결과와 비교, 검증을 거쳐 신뢰성을 얻는다. 본 연구에서는, 3차원 수치모형의 다양한 난류모델을 이용하여 흡입파이프로 물이 유입될 때 흡입부 내, 외의 수심 별 유속 변화를 분석하고, 그 결과를 이용하여 FLOW 3D 모형의 검증을 수행하였다.

• The Journal of the Convergence on Culture Technology
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• v.8 no.5
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• pp.547-552
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• 2022

In this study, shape-based track management by analyzing track irregularity was studied in terms of force-based track irregularity analysis by numerical analysis of wheel-rail interaction force using by the measured vertical irregularity. The effect of the vertical irregularity of the track due to the difference in track types on the wheel-rail interaction force and the track acceleration in the connecting section of the sleeper floating track and the direct fixation track on concrete bed were analyzed. As the results of this study, the measured vertical irregularity was directly affect the vertical wheel load (the wheel-rail interaction force) and the rail acceleration, and it has been demonstrated to change consistently. In this study, the adequacy and necessity of the force-based track irregularity analysis method was verified based on the wheel-rail interaction analysis using the the measured vertical irregularity.

• Journal of the Korean Geotechnical Society
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• v.25 no.1
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• pp.89-99
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• 2009

Compared to standard piling methods, micropile construction can be used in downtown areas since it generates less vibration and noise. Since it only causes less soil disturbance, it is commonly used as reinforcement to existing structures. In this study, a field wherein the bearing capacity and settlement of soil can not support the weight of the superstructure was selected and micropiles were implemented instead of ordinary piles. The deformation modulus of the micropile reinforced ground was determined and was directly reflected in the design. Loading testing was used to check whether or not the allowable bearing capacity satisfies the condition of the designed bearing capacity. The computed deformation modulus based from the test was used in the numerical analysis of soil to investigate the stability of the foundation and analysis method. And a method for controlling the bearing capacity and settlement was recommended.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.45-52
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• 2010

This study pointed on the dynamic impact of AGT (Automated Guide-way Transit) bridge, due to concrete rail prominence. An experiment was done with 30 m P.S.C. bridge in AGT test line in Kyungsan. An artificial prominence with 10 mm hight, was installed at the mid span of concrete rail. And computer simulation was executed for the artificial prominence. As an experiment result, in the case of with prominence, bridge acceleration responses are increased 50% at the speed range of 20 km/h-60 km/h, and bridge displacement responses increased slightly. With these results, the prominence of concrete rail can be induce excess impact and vibration. And the computer program simulated much the same as experiments. So this program can be used for AGT bridge design and formulate the standard of concrete rail management.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.277-284
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• 2024

This study proposes a method to predict noise reduction based on noise-reduction measures, using harmonic response analysis, for transformer design. The dynamic elastic coefficients of the components comprising the actual transformer were determined by manufacturing the materials of the transformer components into simple-shaped specimens, followed by a comparison of the modes between the experiments and the analyses. A finite element model of the transformer was implemented, and harmonic response analysis was performed by deriving the exciting force of the transformer. Subsequently, the theoretical sound power level of the transformer was derived from the results of the harmonic response analysis. Finally, noise reduction measures were established, and the noise reduction amounts were compared between the experiments and the analyses, before and after applying the measures. Through the comparison and analyses of the noise reduction measures, it was confirmed that the trends in the experiments and analyses matched.

• Journal of the Korean Magnetics Society
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• v.13 no.1
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• pp.21-28
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• 2003

M-type hexagonal BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$ (0$\leq$x$\leq$1.0) ferrite powders prepared by a sol-gel method. The crystallographic and magnetic properties were characterized with a x-ray diffraction (XRD), thermogravimetry (TG), differential thermal analysis (DIA), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The result of XRD measurements show that the a and c lattice parameters increase with increasing x from $\alpha$=5.882 and c=23.215 $\AA$ for $\chi$=0.0, to $\alpha$=5.895 and c=23.295 $\AA$ for $\chi$=1.0. From the Mossbauer results, the $Co^{2+}$- $Ti^{4+}$ site occupancies have been affected the changes in the magnetization and in the coercivity. The Curie temperature linearly decreases with increasing $Co^{2+}$- $Ti^{4+}$ concentration x.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.259-265
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• 2012

This paper investigates engineering characteristics of lightweight soils mixed with air foam and tire powder. Lightweight soils could be used as foundation materials, back-fills of reducing vibrating or abutment, and so on. Unconfined and triaxial compression tests were carried out to analyze strength and deformation characteristics of lightweight soils by changing target moist unit weight and cement contents. In comparison with strength characteristics of two different kinds of lightweight soils with same most unit weights ($13kN/m^3$), unconfined compression tests showed similar compressive strength, however, triaxial compression tests showed that compressive strength of lightweight soils mixed with waste tire powder was relatively larger strength than that of lightweight soils mixed with air foam because of elasticity of waste tire powder. Also, unconfined and triaxial compressive strengths of most of lightweight soils increase with increases of moist unit weight and cement contents. However, the strength of lightweight soils mixed with air foam under $11kN/m^3$, when moist unit weight exceeds a certain cement contents, decreases even though cement contents increase because of the effect in a void gap of air foam.