• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.176-176
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• 2011

환형수조는 점착성 퇴적물의 이송특성 연구를 위해 가장 선호되는 실험 장치로 알려져 있다. 과거 많은 연구자들은 퇴적물의 이송특성, 특히 침식/퇴적 특성 조사를 위해 주로 수로를 이용한 실험적 연구를 수행하였는데, 최초의 실험적 연구들은 주로 직선수조에서 수행되었다. 그러나 입자간의 응집이 중요한 역할을 하는 점착성 퇴적물의 경우에, 직선수조 끝단에서의 자유낙하 및 재순환 펌프의 날개에 의해 응집된 토사가 쉽게 분리될 수 있어 그 타당성이 의문시 되어 왔으며, 이러한 단점을 보완하기 위해 환형수조가 고안되었다. 환형수조는 수면과 접하여 회전하는 상부링의 마찰력에 의해 흐름이 생성되기 때문에 시간의 제약 없이 흐름조건을 동일하게 만들 수 있다는 큰 장점을 갖는다. 그러나 환형수조는 원주유속의 속도차이 및 원심력으로 인한 2차 순환류를 형성시켜 반경 방향(radial direction)에서의 바닥전단응력을 불균일하게 하는 단점을 갖는다. 이러한 2차 순환류와 바닥전단응력의 불균일을 저감시키기 위하여 환형수조의 몸체를 상부링의 회전 방향과 역방향으로 직접 회전시키는 방법이 채택되어져 왔다. 한편, 환형수조의 상부링과 몸체를 서로 역방향으로 동시에 회전시키는 양방향 회전(counter-rotation)의 적용을 위해서는 2차 순환류가 최소가 되며 바닥전단응력이 균일해지는 최적 회전속도비에 대한 분석은 필수적 사항이다. 이를 위하여, 상부링과 몸체의 회전속도에 따라 변화하는 수조내부의 흐름특성 및 평균바닥전단응력에 대한 연구가 선행되어야만 한다. 이에 본 연구에서는 전산유체역학을 이용하여 전북대에 설치된 환형수조의 상부링과 몸체의 회전속도에 따라 변화하는 수조내부에서의 흐름특성 및 바닥전단응력에 대한 분석이 수행되었다. 또한, 이를 기초로, 환형수조의 최적 회전속도비 산출을 위한 연구가 수행 중에 있다. 이러한 결과들은 추후 환형수조를 이용한 점착성 퇴적물의 침식/퇴적 등과 같은 이송특성 연구시, 퇴적물에 작용하는 흐름조건의 정밀산정을 위한 기초자료로 활용될 수 있을 것이다.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.135-146
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• 2003

Uphole test is a seismic field test using receivers on ground surface and a source in depth. In this paper, the uphole test using SPT(standard penetration test) which is economical and reliable for obtaining shear wave velocity profile was introduced. In the proposed uphole test, SPT sampler which is common in site investigation, was used as a source and several 1Hz geophones in line were used as receivers. Test procedures in field and interpretation methods for obtaining interval times and for determining shear wave velocity profile considering refracted ray path were introduced. Finally, uphole test was performed at three sites, and the applicability of the proposed uphole test was verified by comparing wave velocity profiles determined by the uphole test with the profiles determined by downhole test, SASW test and SPT-N values.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.1-9
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• 2010

We reported the methodology for the shear test which is one of the evaluation procedure for mechanical reliability of flip-chip package. The shear speed and the tip height are found to be two significant experimental parameters in the shear test. We investigated how these two parameters have an influence on the results, the shear strength and failure mode. In order to prove these experimental inconsistency, simulation using finite element analysis was also conducted to calculate the shear strength and to figure out the distribution of plastic energy inside of the solder ball. The shear strength decreased while the tip height increased or the shear speed decreased. A variation in shear strength due to inconsistent shear conditions made confusion on analyzing experimental results. As a result, it was strongly needed to standardize the shear test method.

• The Journal of Engineering Geology
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• v.32 no.1
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• pp.173-191
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• 2022

In this study, the shear wave velocity of the ground was measured using Flat TDR, and the precision analysis of the measured value and the verification of field applicability were performed. The shear wave velocity measurement value was derived in the field using the piezo-stack combined in the Flat TDR. analyzed. As a result of the experiment, the average value of the change in shear wave speed at the time of grout material injection was 10.15 m/s at the beginning of age, and the average value of the change in shear wave speed after the 7th to 14th days was 65.99 m/s, showing a tendency to increase with age. Also, it was found that dry density and shear wave speed increased as the water content increased on the dry side, and that the dry density and shear wave rate decreased as the water content increased on the wet side as the water content increased. The shear modulus value derived from the field test was confirmed to be a minimum of 17.36 MPa and a maximum of 28.13 MPa, confirming a measurement value similar to the reference value. Through this, it can be seen that the measured value of the shear modulus using Flat TDR is reliable data, and it can be determined that the compaction management of the site can be effectively managed in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.431-443
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• 2006

As part of a fundamental characterization for subsurface layers in Korea, the weathering degree and shear wave velocity ($V_S$) were evaluated from the X-ray fluorescence analyses and the site investigations containing boring and in-situ seismic tests, respectively, for decomposed granite layer in Hongsung. The subsurface layers at Hongsung were composed of 10 to 40 m thickness of weathered layer in most sites. According to the results of weathering degree analyses in Hongsung, it was examined that three chemical weathering indexes such as MWPI, VR and WIP generally increased with decreasing depth. From the in-situ seismic tests, the $V_S$ was determined as the range between 200 and 500 m/s in weathered layer. Based on the $V_S$ and N value at borehole seismic testing sites, N-$V_S$ correlations were established for weathered layer. Furthermore, the relationships of three representative weathering indexes with the $V_S$ and N value indicated that the MWPI, WIP and 100/VR increased linearly as increasing $V_S$ and exponentially as increasing N value.

• The Korean Journal of Rheology
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• v.3 no.1
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• pp.13-21
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• 1991

본연구에서는 단단한 구형 입자가 적은 변형속도에서 2차 유체로 간주될 수 있는 점탄성 용액의 disc-plate (비틀림)흐름에 놓였을 때의 측면 이동속도에 관하여 분석하였다. 이론적 계산을 통해 비틀림 유체 흐름에서 입자는 항상 중심쪽으로 이동하고 안쪽으로의 이 동속도의 크기는 유체의 성질과 흐름의 형태의 함수라는 것을 발견하였으며 이것은 2차 유 체에서 입자는 높은 전단속도 영역에서 낮은 전단속도 영역으로 이동된다는 예측과 일치한 다는 것을 알 수 있었다. 그러나 2차 유체 모델로 부터의 이결과는 이전연구자들에 의해 관 찰된 비틀림 유체 흐름에서의 바깥방향으로의 입자의 이동은 설명하지 못하였다.

• Journal of the Korean Geotechnical Society
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• v.22 no.11
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• pp.47-54
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• 2006

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 ${\alpha}$ parameters and ${\beta}$ exponents that are experimentally determined. The ${\beta}$ exponents are controlled by contact effects of particulate materials (sizes, shapes, and structures of particles) and the ${\alpha}$ 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 evvective 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.

• Elastomers and Composites
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• v.44 no.4
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• pp.423-428
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• 2009

The non-Newtonian flow curves of polyurethane melts were obtained by using a Physica cone-plate rheometer at various temperatures. The rheological parameters were obtained by applying non-Newtonian flow equation to the flow curves for polyurethane samples. When the polyurethane samples are under increasing-decreasing shear rate modes, the hysteresis loop and thixotropic behavior were shown. Polyurethane melts behave as strong gels when they are subjected to shear flow, but when the applied stress surpasses the yield stress, they exhibit non-linear viscoelasticity. Upon decreasing shear rate, its shear stress remains smaller than the values measured in the increasing shear rate mode, because of broken of its structure.

• Land and Housing Review
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• v.2 no.4
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• pp.387-395
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• 2011

According to the seismic design criteria for structural buildings in Korea, the ground is classified into 5 types based on the average shear wave velocity measured from elastic wave tests on site and seismic load applied to the structure is estimated. However, elastic wave tests in site, however, on the engineering fill, cannot be performed during the construction period. Therefore, to evaluate shear wave velocity considering field conditions, resonant column (RC) and torsional shear (TS) tests are performed and compared with various elastic wave test results. As a result, if confining pressure for the tests using engineering fill are considered properly, we can obtain similar results comparing with those of elastic wave tests. In addition, by considering the effect of maximum shear modulus and confining pressure by RC/TS tests, n values shows typical values ranging from 0.434 to 0.561 so that utilization of RC/TS tests can be useful to infer shear modulus in field.

• The Korean Journal of Rheology
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• v.2 no.2
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• pp.56-65
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• 1990

열방성 액정고분자와 폴리카보네이트를 대상 수지로 하여 용융혼합기로 액정고분자 의 함량, 혼합속도 및 온도등의 변환에 따른 훈련 특성을 측정하고 고분자 혼합물의 혼련조 건과 유변학적 특성 모폴로지 사이의 관계를 조사하였다. 혼련 토크는 100rpm의 혼합속도 에서 극소값을 보이며 혼합기 내의 전단속도가 낮기 때문에 혼력에의해서는 LCP가 섬유상 으로 형성되지 못하고 구형의 입자로 존재함을 알수 있었다. 혼합물의 점도는 시험된 전단 속도 영역에서 순수한 고분자보다 현저히 낮으며 5wt%의 소량 첨가로도 5배의 점도 감소 효과를 보이고 LCP함량이 약 30wt%일 경우 점도 및 혼합에너지가 최소로 되었다. Capillary 레오미터의 실험결과 LCP/PC의 점도비가 1보다 작거나 같튼 전단장하에서 LCP 는 섬유상을 형성하였으며 높은 점도비의 경우 LCP의 변형이 어려워 구형의 입자로 존재하 였다. 또한 혼합물의 PC Tg 이동은 에스터르 교환 반응에 의한 부분적인 혼화성의 증가에 기인함을 알수 있었다.