• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2468-2479
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• 1996

An upper bound solution is obtained to perform the process analysis of hot strip rolling process. The material flows within the roll bite at various geometries and frictional conditions are obtained from finite element analysis and the typical flow pattern which is necessary to determine the kinematically admissible velocity field is assumed. From the kinematically admissible velocity field, the upper bound energy is calculated and the rolling load, angle of neutral point and forward slip ratio at various operational conditions are obtained from upper bound energy. The process analysis of above mentioned parameters at various operational conditions have provided valuable information which is hard to obtain during rolling operation and the predicted ranges of quantitive values from these analyses lie whthin the bound of actual operational data.

• Journal of the Korean GEO-environmental Society
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• v.20 no.12
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• pp.41-47
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• 2019

This paper deals with the reliability analysis of foundation for an offshore wind turbine system. Reliability analyses were carried out for suction bucket foundation considering the uncertainties in soil and structural parameters. In reliability analysis, the vertical and lateral resistances are defined as base limit states. The case studies were carried out using the preliminarily designed foundations at western-south mainland sea of Korea. From reliability analyses, vertical resistance for free-slip condition has overall lower reliability index, and submerged unit weight and internal friction angle of seabed soil are governing factors in vertical and lateral resistance in this case.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.148-148
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• 1999

다이아몬드에 버금가는 높은 경도뿐만 아니라 높은 화학적 안정성 및 열전도성 등 우수한 물리화학적 특성을 가진 입방정 질화붕소(cubic Boron Nitride)는 마찰.마모, 전자, 광학 등의 여러 분야에서의 산업적 응용이 크게 기대되는 자료이다. 특히 탄화물형성원소에 대해 안정하여 철계금속의 가공을 위한 공구재료로의 응용 또한 기대되는 재료이다. 특히 탄화물형성원소에 대해 안정하여 철계금속의 가공을 위한 공구재료로의 응용 또한 크게 기대된다. 이 때문에 각종의 PVD, CVD 공정을 이용하여 c-BN 박막의 합성에 대한 연구가 광범위하게 진행되어 많은 성공사례들이 보고되고 있다. 그러나 이러한 c-BN 박막의 유용성에도 불구하고 아직 실제적인 응용이 이루어지지 못한 것은 증착직후 급격한 박리현상을 보이는 c-BN 박막의 밀착력문제때문이다. 본 연구에서는 평행자기장을 부가한 ME-ARE(Magnetically Enhanced Activated Reactive Evaporation)법을 이용하여 c-BN 박막을 합성하고, 합성된 c-BN 박막의 밀착력에 미치는 공정인자의 영향을 규명하여, 급격한 박리현상을 보이는 c-BN 박막의 밀착력 향상을 위한 최적 공정을 도출하고자 하였다. BN 박막 합성은 전자총에 의해 증발된 보론과 (질소+아르곤) 플라즈마의 활성화반응증착(activated reactive evaporation)에 의해 이루어졌다. 기존의 ARE장치와 달리 열음극(hot cathode)과 양극(anode)사이에 평행자기장을 부여하여 플라즈마를 증대시켜 반응효율을 높혔다. 합성실험용 모재로는 p-type으로 도핑된 (100) Si웨이퍼를 30$\times$40 mm크기로 절단 후, 100%로 희석된 완충불산용액에 10분간 침적하여 표면의 산화층을 제거한후 사용하였다. c-BN 박막을 얻기 위한 주요공정변수는 기판바이어스 전압, discharge 전류, Ar/N가스유량비이었다. 증착공정 인자들을 변화시켜 다양한 조건에서 c-BN 박막의 합성하여 밀착력 변화를 조사하였다. 합성된 박막의 결정성 분석을 FTIR을 이용하였으며, Bn 박막의 상 및 미세구조관찰을 위해 투과전자현미경(TEM;Philips EM400T) 분석을 병행하였고, 박막의 기계적 물성 평가를 위해 미소경도를 측정하였다. 증착된 c-BN 박막은 3~10 GPa의 큰 잔류응력으로 인해 증착직후 급격한 박리현상을 보였다. 이의 개선을 위해 증착중 기판바이어스 제어 및 후열처리를 통해 밀착력을 수~수백배 향상시킬 수 있었다. c-BN 박막의 합성을 위해서는 증착중인 박막표면으로 큰 에너지를 갖는 이온의 충돌이 필요하기 때문에 기판 바이어스가 요구되는데, c-BN의 합성단계를 핵생성 단계와 성장 단계로 구분하여 인가한 기판바이어스를 달리하였다. 이 결과 그림 1에서 나타낸 것처럼 c-BN 박막의 핵생성에 필요한 기판바이어스의 50% 정도만을 인가하였을 때 잔류응력은 크게 경감되었으며, 밀착력이 크게 향상되었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.9-23
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• 1997

A numerical study of a two-layer, stratified flow is investigated, using the implicit finite difference method in one dimension. The results of computational method have been tested and, in case of lock exchange flow, compared with the results of experimental data. The results of model experiments with various interfacial, bottom friction coefficients along with various time weighting factor of numerical scheme and dissipative interface are shown and discussed. Two-layer model experiment has been also carried out to investigate the generation and propagation characteristics of internal tidal wave over the steep bottom topography under stratified condition. The internal wave seems to well radiate through the downstream boundary under the experiments adopting radiation conditions both at two layers and only at upper layer, confirming the applicability of radiational boundary condition in stratified flows. It is also shown that the internal wave through the downstream boundary propagates more actively with increasing thickness of lower layer in the downstream. This implies that the potential tidal energy in the interface will depend upon the thickness of lower layer for the constant thickness of upper layer.

• Journal of the Korean GEO-environmental Society
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• v.11 no.1
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• pp.13-18
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• 2010

It is crucial to decide reasonably the parameters necessary for design through research on the characteristics of rock in order to analyze stability of rock structure. This article has conducted both pressure meter test, uniaxial and triaxial compression test to the areas of andesite or tuff located in local regions such as Yeosu, Gwangju, Yangsan, Busan, and Daejeon and has comparatively analyzed previously proposed estimative formulas. According to the result of estimating the deformation modulus through using the damping coefficient suggested by Nicholson & Bieniawski, when RMR is less than 60, it is desirable to use the result of the pressure meter test considering the damping coefficient. If the RMR value is over 60, however, the formula suggested by Kim Gyo-won has been proved to be the most applicable. Moreover, according to the result of comparing the RMR, adhesion, and angle of internal friction, both the adhesion and angle of internal friction best correspond to the formula proposed by Tsuchiya. Comparatively analyzing the relations between the rock deformation modulus and RMR and also suggesting the formula of calculating the shear strength parameter to use the RMR value, this study did not include the deformation modulus and shear strength parameter as factors to decide the RMR index. Since result can differ by several factors, it will be necessary afterwards to suggest practical estimative formulas applicable to the actual spots of Korea.

• The Journal of Engineering Geology
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• v.27 no.1
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• pp.91-101
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• 2017

Fault materials has various properties depending on their areas, rock types, and components because they are formed by heterogeneous and complicated mechanisms. In this study, to understand the physical and mechanical properties of fault materials, 109 fault materials distributed in South Korea were collected to conduct various laboratory tests with them and analyze their physical and mechanical properties (unit weight, specific gravity, porosity, gravel content, silt/clay content, clay mineral content, friction angle, and cohesion) according to areas, rock types, and components. As for the physical and mechanical properties by rock type, gneiss shows the highest medians in the unit weight ($17.1kN/m^3$) and specific gravity (2.73), granite does so in the porosity (45.5%), schist does so in the gravel content (20.0 wt.%) and cohesion (38.1 kPa), and phyllite does so in the silt/clay content (54.4 wt.%), clay mineral content (30.1 wt.%), and friction angle ($38.2^{\circ}$). With regard to the physical and mechanical properties by component, fault gouge was shown to have lower values than cataclasite and damage zones in all factors other than porosity and silt/clay contents.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.316-323
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• 2013

The use of artificial roughness in various forms of shapes and sizes is the most common and effective way to improve the performance of a flat-plate solar collector. In the present study, numerical analysis on heat transfer and pressure drop was performed in a rectangular channel with various rib arrays. The uniform heat flux is applied to the channel from the upper side. The forms of ribs considered in this study were rib $90^{\circ}$, groove $90^{\circ}$, groove $60^{\circ}$, baffle $90^{\circ}$, baffle $60^{\circ}$, wave $90^{\circ}$ and wave $60^{\circ}$. Air is the working fluid, and the Reynolds number ranges from 3200 to 17800. Nusselt number and friction factor were investigated to predict the performance of the system with various type of ribs. The average Nusselt number and pressure drop were increased with the increase of velocity in all types of ribs. The highest heat transfer and pressure drop occurred for the baffle $90^{\circ}$, but highest performance factor considering heat transfer and pressure drop together occurred for the groove $60^{\circ}$. Therefore, heat transfer and pressure drop should be considered together when a flat plate solar collector is designed.

• Journal of Korean Ophthalmic Optics Society
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• v.9 no.1
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• pp.145-159
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• 2004

A mathematical model and its computer solution program were proposed to analyze the motion of contact lenses which are being subject to lid-blinking. The equation was derived by incorporating an acceleration induced lid's force exerting on the contact lens, the viscous damping resistance in the tear layer beneath the lens and the sliding frictional force between the lid and the contact lens surface into the formulation of differential equation describing the vibration. The model predicts the time-dependent displacement from the equilibrium postion during/after the blinking. During the blinking, as the time for the completion of one cycle of blinking decreases the off-the-equilibrium displacement of contact lens increases while the decrease of diameter in the contact cause the opposite effect. It is found that lid pressure exerting on the lens cause an insignificant lens displacement from the equilibrium position. After blinking the frequency of damped oscillation of contact lens decreases as the diameter of lens increases, due to the incresed surface while the reduced blinking time does not cause a significant frequency change. This is because that driving force for the contact lens movement posterior to blinking is the capillary-induced force not the lid force.

• Journal of Biosystems Engineering
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• v.7 no.2
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• pp.57-71
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• 1983

마찰식 정미기의 성능에 영향을 미치는 기계설계 및 작동상의 인자로는 스크린의 형태, 롤러의 형태, 롤러회전속도, 출구 저항 등 여러가지가 있다. 이러한 요인들에 대한 연구가 본 논문의 저자에 의해서 시리즈로 연구되어 왔으며, 본 연구는 그의 일환으로 스크린의 단면형상(6각, 8각, 12각 그리고 원통형), 스크린에 뚫려있는 슬랏의 기울기($15^{\circ}$, $30^{\circ}$, $45^{\circ}$ 그리고 $-45^{\circ}$), 그리고 출구 저항이 정백미의 질과 양, 정백효율 그리고 정백실내의 정백압력 등에 미치는 영향을 규명하기 위해 수행되었다. 이 실험에 사용된 공시 정미기는 임도정 공장에서 널리 사용되고 있는 흡입마찰식이었며, 사용된 시료는 밀양 23호인 통일계품종이었다. 각 처리마다 동력 소모량과 정백실내의 정백압력을 측정하기 위해서 "KYOWA" 스트레인 게이지 시스템(strain gauge system), 토오크 변환기, 압력변환기 등이 사용되었다. 본 실험 결과를 요약하면 다음과 같다. 1) 정백과정중에 정백실내의 정백압력은 입구에서 가장 높았고 출구쪽으로 갈수록 점차 감소하였다. 평균 정백압력도 순환 횟수에 따라서 변화 하였는데 첫번째 순환에서 가장 높았고 순환횟수가 증가함에 따라 감소하였다. 2) 본 실험에서 사용한 출구저항 수준은 출구저항 수준 1에서 요구되는 정백도의 백미를 얻기 위한 순환 횟수는 2회 이었고 출구저항 수준 2에서는 4회 이었는데, 이를 출구저항 수준이 정백압력, 정백율, 완전미수율 및 도정 효율에 가장 큰 영향을 주었다. 3) 스크린에 뚫려있는 슬랏 각도가 $15^{\circ}$에서 $45^{\circ}$로 증가함에 따라서 정백실내의 평균 정백압력은 감소하였고, 완전미수율과 도정 효율은 증가하였으나, 일반적으로 도정수율은 감소하는 경향을 보였다. $-45^{\circ}$의 슬랏 각도를 가진 스크린에서는 슬랏 각도 $15^{\circ}$인 스크린에서와 거의 비슷한 정백압력 수준을 나타냈으나 완전미와 정백미의 생산은 매우 낮았다. 4) 스크린 표면에 기다란 강편 (보통 "띠"라고 부름)을 붙인 원통과 12각형의 스크린에서는 강편을 붙이지 않은 6각형과 8각형 스크린에서 보다는 비교적 높은 정백압력을 나타냈다. 전자는 후자에 비해서 정백효율은 높았으나 완전미수율은 떨어졌다. 5) 정백실내에서 가장 낮은 정백압력을 나타낸 8각형 스크린은 높은 도정수율과 완전미수율을 가져왔으나 상대적으로 정백효율은 낮게 나타났다. 6) 정백실내의 반경 방향의 평균 정백압력($P_R$)과 완전미수율($Y_h$)은 다음과 같은 1차적인 역비례 관계가 있었으며(평균 정백압력 범위는 0.5-0.9kg/$cm^2$), $Y_h=-28.661P_R+84.860$ ($r^2=0.858$) 정백효율($Y_e$)과 정백압력($P_R$) 사이에는 다음과 같은 2차적인 관계가 존재함을 알 수 있었다. $Y_e=-597.5P_{R^2}+929.96P_R-210.15$ ($r^2=0.759$) 정백효율은 정백압력이 0.7-0.8kg/$cm^2$일 때 가장 높았으며, 이때 변이도 가장 심한 것으로 나타났다.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.67-76
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• 2011

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. Adfreeze bond strength is considered to be the most important design parameter for foundations in cold region. Many studies in last 50 years have been conducted to analyze characteristics of adfreeze bond strength. However, most studies have been performed under constant temperature and normal stress conditions in order to analyze affecting factors like soil type, pile material, loading speed, etc. In this study, both freezing temperature and normal stress acting on pile surface were considered to be primary factors affecting adfreeze bond strength, while other factors such as soil type, pile material and loading speed were predefined. Direct shear box was used to measure adfreeze bond strength between Joomoonjin sand and aluminium because it is easy to work for various roughness. Test was performed with temperatures of > $0^{\circ}C$, $-1^{\circ}C$, $-2^{\circ}C$, $-5^{\circ}C$, and $-10^{\circ}C$ and vertical confining pressures of 1atm, 2atm, and 3atm. Based on the test results, the effects of temperature and vertical stress on adfreeze bond strength were analyzed. The test results showed that adfreeze bond strength increases with decreased temperature and increased vertical stress. It was also noted that two types of distinct sections exist, owing to the rate of increase of adfreeze bond strength along the change of freezing temperature: 1)rapidly increasing section and 2)gradually decreasing section. In addition, the results showed that a main factor affecting adfreeze bond strength switches from friction angle to adhesion as freezing temperature decreases.