• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1466-1483
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• 2008

This paper discusses the development of an up-to-date computerized CPT (Cone Penetration Test) based soil engineering classification system to provide geotechnical engineers with a handy tool for their daily design activities. Five CPT soil engineering classification systems are incorporated in this effort. They include the probabilistic region estimation and fuzzy classification methods, both developed by Zhang and Tumay, the Schmertmann, the Douglas and Olsen, and the Robertson et al. methods. In the probabilistic region estimation method, a conformal transformation is used to determine the soil classification index, U, from CPT cone tip resistance and friction ratio. A statistical correlation is established between U and the compositional soil type given by the Unified Soil Classification System (USCS). The soil classification index, U, provides a soil profile over depth with the probability of belonging to different soil types, which more realistically and continuously reflects the in-situ soil characterization, which includes the spatial variation of soil types. The CPT fuzzy classification on the other hand emphasizes the certainty of soil behavior. The advantage of combining these two classification methods is realized through implementing them into visual basic software with three other CPT soil classification methods for friendly use by geotechnical engineers. Three sites in Louisiana were selected for this study. For each site, CPT tests and the corresponding soil boring results were correlated. The soil classification results obtained using the probabilistic region estimation and fuzzy classification methods are cross-correlated with conventional soil classification from borings logs and three other established CPT soil classification methods.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2007년 가을학술발표회
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• pp.266-292
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• 2007

Round Robin Test (RRT) on ground response analyses was conducted for three sites in Korea based on several site investigation data, which include borehole logs with the N values from standard penetration test (SPT) for all three sites and additionally cone tip resistance profiles for two sites. Three input earthquake motions together with the site investigation data were provided for the RRT. A total of 12 teams participating in this RRT presented the results of ground response analyses using equivalent-linear and/or nonlinear method. Each team determined input geotechnical properties by using empirical relationships and literatures based on own judgment, with the exception of the input motions. Herein, the characteristics of input motions were compared in terms of the frequency and period, and the selection of the depth to bedrock, on which the motions is impinged, was discussed considering geologic conditions in Korea. Furthermore, a variety of geotechnical properties such as shear wave velocity profiles and soil nonlinear curves were investigated with the input properties used in this RRT.

• 대한치과교정학회지
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• 제47권4호
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• pp.238-247
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• 2017

Objective: The aim of this study was to compare recycled and unused orthodontic miniscrews to determine the feasibility of reuse. The comparisons included both miniscrews with machined surfaces (MS), and those with etched surfaces (ES). Methods: Retrieved MS and ES were further divided into three subgroups according to the assigned recycling procedure: group A, air-water spray; group B, mechanical cleaning; and group C, mechanical and chemical cleaning. Unused screws were used as controls. Scanning electron microscopy, energy-dispersive X-ray spectrometry, insertion time and maximum insertion torque measurements in artificial bone, and biological responses in the form of periotest values (PTV), bone-implant contact ratio (BIC), and bone volume ratio (BV) were assessed. Results: Morphological changes after recycling mainly occurred at the screw tip, and the cortical bone penetration success rate of recycled screws was lower than that of unused screws. Retrieved ES needed more thorough cleaning than retrieved MS to produce a surface composition similar to that of unused screws. There were no significant differences in PTV or BIC between recycled and unused screws, while the BV of the former was significantly lower than that of the latter (p < 0.05). Conclusions: These results indicate that reuse of recycled orthodontic miniscrews may not be feasible from the biomechanical aspect.

• 마이크로전자및패키징학회지
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• 제15권2호
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• pp.47-54
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• 2008

컴포넌트에서의 비정상적인 금속간화합물 성장이 보드 레벨 기계적 신뢰성에 미치는 영향을 연구하기 위하여, 전기 도금된 Ni/Au UBM과 Sn2.5Ag0.5Cu 솔더의 리플로우 횟수 및 고온 시효 시간에 따른 금속간 화합물 성장거동을 관찰하였다. 각 조건별로 처리된 컴포넌트에서 솔더 접합부의 기계적 특성을 비교하기 위하여, 전단 속도 변화에 따른 볼 전단 시험을 실시하여 전단에너지 값을 측정하였다. 마지막으로, 보드 레벨에서의 기계적 신뢰성 시험을 위하여 조건별로 처리된 컴포넌트를 PCB 보드에 실장하여, 3점 굽힘 시험 및 충격 시험을 실시한 후 파괴모드를 분석하였다.

• 대한기계학회논문집B
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• 제21권9호
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• pp.1149-1164
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• 1997

In this study, the applicability of the RNG k-.epsilon. model to the analysis of the complex flows is studied. The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretized by the finite volume method with non-staggered variable arrangements. The predicted results using the RNG k-.epsilon. model of three complex flows, i.e., the flow over a backward-facing step and a blunt flat plate, the flow around a 2D model car are compared to these from the standard k-.epsilon. model and experimental data. That of the unsteady axisymmetric turbulent flow within a cylinder of reciprocating model engine including port/valve assembly and the spray characteristics within a chamber of direct injection model engine are compared to these from the standard k-.epsilon. model and experimental data. The results of reattachment length, separated eddy size, average surface pressure distribution using the RNG k-.epsilon. model show more reasonable trends comparing with the experimental data than those using the modified k-.epsilon. model. Although the predicted rms velocity using the modified k-.epsilon. model is lower considerably than the experimental data in incylinder flow with poppet valve, predicted axial and radial velocity distributions at the valve exit and in-cylinder region show good agreements with the experimental data. The spray tip penetration predicted using the RNG k-.epsilon. model is more close to the experimental data than that using the modified k-.epsilon. model. The application of the RNG k-.epsilon. model seems to have some potential for the simulations of the unsteady turbulent flow within a port/valve-cylinder assembly and the spray characteristics over the modified k-.epsilon. model.

• 한국군사과학기술학회지
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• 제19권5호
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• pp.618-628
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• 2016

The development of new concepts of liners is required in order to effectively neutralize the enemy's attack power concealed in the armored vehicles. A multiple-layer liner is one of possibilities and has a mechanism for explosion after penetrating the target which is known as "Behind Armor Effect." The multiple-layer explosive liner should have sufficient kinetic energy to penetrate the protective structure and explosive material react after target penetration. With this in mind, double-layer liner materials were obtained by cold spray coating methods and these material properties were experimentally characterized and used in this simulation for double-layer liners. In this study, numerical simulations in the three different layer types, i.e., single, A/B, A/B/A in terms of the layer location were verified in terms of finite element mesh sizes and numerical results for the jet tip velocity, kinetic energy, and the corresponding jet deformation characteristics were analysed in detail depending on the structure of layer types.

• 한국지반공학회논문집
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• 제35권10호
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• pp.67-78
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• 2019

친환경 지반개량공법인 EICP 처리를 통해 실내 및 현장 실험을 실시하여 미세먼지 억제 효율을 평가하였다. 실내 실험에서는 현장 적용성을 고려하여 저렴한 물질로 EICP 용액을 제작하였으며, EICP 용액의 최적 혼합비 및 처리량을 산정하였다. 용액의 최적 혼합비는 요소/염화칼슘의 비율이 1.5 및 백태가루 15g/L일 경우, 최적의 탄산칼슘 생성량을 보였다. EICP 용액 최적 처리량은 $7L/m^2$이며, 미세먼지 억제 실험 및 콘팁저항치 측정 실험을 통해 결정되었다. 현장 실험은 덤프트럭이 통행하는 test-bed에서 살수 실험 및 EICP 실험을 각각 실시하였으며, 현장의 상황에 따라 효율적인 미세먼지 억제법은 달라질 것으로 판단된다.

• 대한금속재료학회지
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• 제47권12호
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• pp.834-841
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• 2009

A study on the welding of electrogalvanized TRIP (Transformation-Induced Plasticity) steels was done to compare the life of the electrode and the alloying phenomena on the electrode tip surface using singlephase AC and inverter-DC resistance welding processes. A longer life of the electrode (>200 welds) was achieved using the inverter-DC welding process. The tensile shear strength was higher in the electrode life test when welded with the inverter DC welding machine it maintained a higher value even when the welding nugget diameter was smaller than specified. When spot-welding was conducted using the single-phase AC welding process, a higher wear rate of the electrode was observed compared to that with the inverter-DC process. An alloying layer used to determine the rate of electrode growth showed differences in the metallurgical features of the surface alloying and Zn penetration depending on whether the single-phase AC process or the inverter-DC welding process was used. Moreover, changes in the dynamic resistance during the electrode life test were correlated with the electrode wear (or growth) rate.

• 한국분무공학회지
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• 제27권2호
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• pp.57-65
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• 2022

The purpose of this study is to use machine learning to build a model capable of predicting the flash boiling spray characteristics. In this study, the flash boiling spray was visualized using Shadowgraph visualization technology, and then the spray image was processed with MATLAB to obtain quantitative data of spray characteristics. The experimental conditions were used as input, and the spray characteristics were used as output to train the machine learning model. For the machine learning model, the XGB (extreme gradient boosting) algorithm was used. Finally, the performance of machine learning model was evaluated using R² and RMSE (root mean square error). In order to have enough data to train the machine learning model, this study used 12 injectors with different design parameters, and set various fuel temperatures and ambient pressures, resulting in about 12,000 data. By comparing the performance of the model with different amounts of training data, it was found that the number of training data must reach at least 7,000 before the model can show optimal performance. The model showed different prediction performances for different spray characteristics. Compared with the upstream spray angle and the downstream spray angle, the model had the best prediction performance for the spray tip penetration. In addition, the prediction performance of the model showed a relatively poor trend in the initial stage of injection and the final stage of injection. The model performance is expired to be further enhanced by optimizing the hyper-parameters input into the model.

• 한국지반공학회논문집
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• 제26권4호
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• pp.37-45
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• 2010

기후변화로 인해 물의 증발량이 많은 지역의 지반에서는 자연적인 소금의 고결화 현상이 발생한다. 이러한 소금의 고결화 분포는 모래지반에서 모세관력에 영향을 받는다. 이 연구의 목적은 콘 관입시험, 전기전도율 측정, 사진 이미지 촬영, 비파괴 이미지 분석 그리고 탄성파에 의한 프로세스 모니터링을 이용하여 소금의 고결화 현상에 대한 모세관력의 효과를 관찰하는 것이다. 실험은 입상재료를 모형화한 글라스비즈를 소금물에 포화시킨 후, 오븐에 넣어 시료를 건조시킴으로써 고결화를 발생시켰다. 실험결과, 고결된 소금의 농도는 시료입경이 작은 경우 최상부에서 높았고, 시료입경이 큰 경우 중간 또는 하부에서 높았다. 고결된 시료에서 높은 소금농도의 위치는 해석적 방법으로 산정된 모세관 높이와 유사하였다. 본 연구에서 수행한 5가지 실험은 모세관력이 소금이 고결된 흙과 같은 입상재료의 거동에 중요한 영향을 끼치는 것을 보여준다.