• 대한기계학회논문집
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• 제13권4호
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• pp.611-617
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• 1989

본 연구에서는 제트 분사 시스템을 제작하여 절단 성능에 관게하는 여러 변수중 고압수의 압력, 연마제의 크기 및 공급량, 그리고 공작물의 이송속도의 영향을 실험적으로 연구하였다.

• 대한기계학회논문집
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• 제13권4호
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• pp.660-669
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• 1989

본 논문에서는 쐐기형 다이를 이용한 판재의 인발에 대한 슬립라인장에서 스트레인을 구하는 방법을 제시하고 이로부터 가공중에 생길 수 있는 역학적 문제의 공학적 해석을 얻고자 한다.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.171-176
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• 2007

An important challenging issue in the automotive industry is the light-weight, safe design and enhancement of crash response of an auto-body structures. These objectives lead to increasing adoption of high strength steel sheet for inner and outer auto-body members. This paper evaluates the dynamic tensile characteristics of high strength steel sheets, HS45R, TRIP60, DP60 and DP100, along the rolling direction and transverse direction. Static tensile tests were carried out at the strain rate of 0.003/sec using the static tensile machine (Instron 5583). Dynamic tensile tests were carried out at the range of strain rate from 0.1/sec to 200/sec using a high speed material testing machine developed. The tensile tests acquire stress-strain relation and strain rate sensitivity of each material. The experimental results show two important aspects for high strength steels: the flow stress increases as strain rate increases; the strain hardening decreases as the tensile stress increases. The experiments also produce interesting results that the elongation does not decrease even when the strain rate increases.

• Journal of Welding and Joining
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• 제25권4호
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• pp.58-64
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• 2007

Recently, the electro-magnetic induction process has been utilizing to substitute the flame heating process in shipyard. However, few studies have been performed to exactly analyze the deformation mechanism of the heating process with mathematical model. This is mainly due to the difficulty of modeling the inductor travelling on plate during the process. In this study, heat flux distribution of the process is firstly numerically analysed with the assumption that the process has a quasi-stationary state and also with the consideration that the heat source itself highly depends on the temperature of base plate. With the heat flux, the thermal and deformation analyses are then performed with a commercial program for 34 combinations of heating parameters. The deformations obtained and heating parameters are synthesized with a statistical method to produce simplified formulas, which easily give the relation between the heating parameters and deformations. The formulas are well compared with results of experiment.

• Computers and Concrete
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• 제22권6호
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• pp.573-592
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• 2018

An analytical methodology for the calculation of the flexural and the shear capacity of concrete members with Fibre-Reinforced-Polymer (FRP) bars as tensional reinforcement is proposed. The flexural analysis is initially based on the design provisions of ACI 440.1R-15 which have properly been modified to develop general charts that simplify computations and provide hand calculations. The specially developed charts include non-dimensional variables and can easily be applied in sections with various geometrical properties, concrete grade and FRP properties. The proposed shear model combines three theoretical considerations to facilitate calculations. A unified flexural/shear approach is developed in flow chart which can be used to estimate the ultimate strength and the expected failure mode of a concrete beam reinforced with longitudinal FRP bars, with or without transverse reinforcement. The proposed methodology is verified using existing experimental data of 138 beams from the literature, and it predicts the load-bearing capacity and the failure mode with satisfactory accuracy.

• Smart Structures and Systems
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• 제29권5호
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• pp.747-755
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• 2022

Hierarchical structure parameters, proposed in She-Leveque model, are investigated for velocity components obtained from different flow types over a large range of Reynolds numbers 255 < Re_𝜆 < 720. The values of intermittency parameter 𝛽, with respect to a fixed velocity component, are observed nearly same for all four types of turbulence. The parameter 𝛾, for streamwise velocity components is nearly the same but significantly different for vertical components in different flows. It is also observed that for both parameters, an obvious relation between the longitudinal and transverse components 𝛽_T < 𝛽_L (and 𝛾_T < 𝛾_L) always holds. However, the difference between 𝛽_L and 𝛽_T is found very small in all types of turbulent flows, we studied here. It is evidenced that at low Reynolds numbers, the deviations from K41 scaling are mainly due to the most intense structures and slightly because of more heterogeneous hierarchy of fluctuation structures. However, at higher Reynolds numbers the deviations seem as a consequence of the most intense structures only. Over all, the study suggests that the hierarchy parameter 𝛽 may be consider as a universal constant.

• 대한토목학회논문집
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• 제39권2호
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• pp.297-306
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• 2019

개수로 만곡부에서 흐름은 원심력이 작용하기 때문에 횡방향 수면경사가 나타나고 유심선은 만곡 외측으로 치우친다. 수중 수제는 만곡부의 다양한 공학적인 문제를 해결하는 데 사용될 수 있다. 수중 수제가 흐름방향과 이루는 입사각과 수제 열 간격이 만곡부의 하상변동과 편수위에 미치는 영향을 파악하기 위해서 $90^{\circ}$만곡 직사각형 단면 수로에 잔자갈을 깔고 이동상 수리실험을 하였다. 만곡부에 수중 수제를 설치하면 최대 세굴심은 증가하나 균일한 둔각으로 수제를 설치하면 세굴을 줄일 수 있다. 수제를 설치한 만곡부에 수제설치 기준하상의 형성유량과 같은 유량이 흐를 경우 최대 세굴이 발생하는 위치가 하류로 이동하고 편수위는 증가한다. 그 유량보다 작으면 최대 세굴심의 위치가 상류로 이동하며 편수위는 감소한다. 만곡부에서 수중 수제는 입사각, 유량, 수제 열 간격의 상호작용에 따라 하상변동과 편수위에 대한 영향이 다르다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1996년도 The 9th KACG Technical Annual Meeting and the 3rd Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.522-522
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• 1996

An investigation of the effects of transverse magnetic field and Peltier effect on melt convection and macrosegregation in vertical Bridgman crystal grosth of Te doped InSb was been carried out by means of microstructure observation, Hall measurement, electrical resistivity measurement and X-ray analysis. Before the experiments, Interface stability, convective instability and suppression of convection by magnetic field were calculated theoretically. After doping 1018, 1019 cm-3 Te in InSb, the temperature of Bridgman furnace was set up at $650^{\circ}C$. The samples were grown in I.D. 11mm, 100mm high quartz tube. The velocity of growth was about 2${\mu}{\textrm}{m}$/sec. In order to obtain the suppression of convection by magnetic field in the middle of growth, 2-4KG magnetic field was set on the melt. For searching of the shape of solid-liquid interface and the actual velocity of crystal growth, let 2A current flow from solid to liquid for 1second every 50seconds repeatedly (Peltier effect). The grown InSb was polycrystal, and each grain was very sharp. There was no much difference between the sample with and without magnetic field at a point of view of microstructure. For the sample with Peltier effect, the Peltier marks(striation) were observed regularly as expected. Through these marks, it was found that the solid-liquid interface was flat and the actual growth velocity was about 1-2${\mu}{\textrm}{m}$/sec. On the ground of theoretical calculation, there is thermosolutal convection in the Te doped InSb melt without magnetic field in this growth condition. and if there is more than 1KG magnetic field, the convection is suppressed. Through this experiments, the effective distribution coefficients, koff, were 0.35 in the case of no magnetic field, and 0.45 when the magnetic field is 2KG, 0.7 at 4KG. It was found that the more magnetic field was applied, the more convection was suppressed. But there was some difference between the theoretical calculation and the experiment, the cause of the difference was thought due to the use of some approximated values in theoretical calculation. In addition to these results, the sample with Peltier effect showed unexpected result about the Te distribution in InSb. It looked like no convection and no macrosegregation. It was thought that the unexpected behavior was due to Peltier mark. that is, when the strong current flew the growing sample, the mark was formed by catching Te. As a result of the phenomena, the more Te containing thin layer was made. The layer ruled the Hall measurement. The values of resistivity and mobility of these samples were just a little than those of other reference. It was thought that the reason of this result was that these samples were due to polycrystal, that is, grain boundaries had an influence on this result.

• 한국지반공학회지:지반
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• 제3권4호
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• pp.41-54
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• 1987

본 논문에서는 무한사면에서 강우에 따른 지하수위 변동을 합리적으로 추정할 수 있는 추계론적 수치해석모델이 개발되었다. 특히, 투수계수, 비산출율(Specific Yield) 등의 지하수흐름에 필요한 계수들과 지하암반층의 공간적 변화에 의하여 지하수위가 공간적으로 변하는 효과에 관해 중점적으로 연구하였으며, 이러한 계수들의 공간적 변화를 추정하기 위하여 Kriging 이론을 도입하였다. Kriging 이론은 몇개의 제한된 실측치로부터 실측을 하지 못한 각각의 수치해석 요소에 불편, 최소 분산을 갖는 값들을 추정할 수 있는 방법이다. 사면방향의 일차원 수치해석 모델, Kriging 이론, 1차근사해법을 조합하여 추계론적 1차원 수치해석 프로그램을 개발하였다. 또한 사면방향의 지하수위 변동뿐만 아니라, 횡방향의 변동도 조사하기 위하여 확정론적 2차원 모델도 개발하였다. 한 무한사면에 대하여 개발된 모델을 이용하여 예제해석을 한 결과 투수계수나 비산출율의 공간적 변화뿐만 아니라 지하암반층의 공간에 따른 요철도 지하수위의 공간적 변화에 큰 영향을 미침을 알게 되었다. 또한 지하수위는 사면방향으로 큰 변동을 보일뿐 아니라 횡방향으로의 변동 또한 무시할 수 없을 정도로 큼을 알 수 있었다. 개발된 모델의 결과들은 지하수위 변동에 의한 산사태 위 험도 분석시에 이용될 수 있다.

• 한국지반환경공학회 논문집
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• 제16권5호
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• pp.55-66
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• 2015

우리나라 남서해안의 조차는 지역에 따라 3~8m까지 발생하며 이 지역의 풍력기초들은 조류의 다양한 흐름에 의한 세굴로 전체 구조물에 예상치 못한 진동에 의한 장기적인 불안정성이 야기될 수 있다. 본 연구에서는 흐름방향을 고려할 수 있도록 개선된 관수로식 수리저항성능 실험기를 이용하여 압밀압력과 흐름방향의 변화가 지반의 수리저항성능에 미치는 영향을 검토하였다. 실험결과 양방향 흐름에 노출된 시료의 세굴률이 일방향 흐름에서보다 크며, 한계전단응력은 감소하여 세굴에 더욱 취약해지는 것으로 나타났다. 또한 압밀압력이 증가함에 따라 세립질 토사의 한계전단응력과 같은 수리저항특성은 증가하여 세굴에 대한 저항성이 증가하나 조립토의 수리저항 성능은 크게 변화하지 않았다. 지반공학적 특성과 수리저항특성의 상관관계를 검토한 결과, 비배수전단강도는 한계전단응력과 비례관계이며 세립토 및 조립토의 흙 분류와 관계없이 하나의 상관관계로 효과적으로 한계전단응력을 예측할 수 있는 것으로 나타났으며 전단파 속도는 한계전단응력과 비례관계에 있으며 조립토와 세립토의 영역에 따라 비교적 명확히 구분되었다.