• Structural Engineering and Mechanics
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• 제71권6호
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• pp.699-712
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• 2019

The reinforced concrete lining of hydraulic pressure tunnels tends to crack under high inner water pressure (IWP), which results in the inner water exosmosis along cracks and involves typical hydro-mechanical interaction. This study aims at the development, validation and application of an indirect-coupled method to simulate the lining cracking process. Based on the concrete damage plasticity (CDP) model, the utility routine GETVRM and the user subroutine USDFLD in the finite element code ABAQUS is employed to calculate and adjust the secondary hydraulic conductivity according to the material damage and the plastic volume strain. The friction-contact method (FCM) is introduced to track the lining-rock interface behavior. Compared with the traditional node-shared method (NSM) model, the FCM model is more feasible to simulate the lining cracking process. The number of cracks and the reinforcement stress can be significantly reduced, which matches well with the observed results in engineering practices. Moreover, the damage evolution of reinforced concrete lining can be effectively slowed down. This numerical method provides an insight into the cracking process of reinforced concrete lining in hydraulic pressure tunnels.

• 보건의료생명과학 논문지
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• 제9권2호
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• pp.245-252
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• 2021

본 연구는 COVID-19 팬데믹 상황에서 대학생들이 선호하는 강의방법 및 대학생활을 알아보고자 설문조사를 하였다. 설문에는 광주, 전남, 전북에 소재한 전문대학 학생들이 참여하였다. 연구의 주된 결과는 모든 학년에서 비대면 강의 방법을 선호하는 것으로 나타났지만, 대면강의와 비대면 강의 혼합방법도 선호하는 것으로 나타났다(p=0.923). 강의 방법별 교육만족도에서는 대면강의의 만족도 점수가 2.82점으로 가장 높게 나타났다(p=0.000). 그러나 학업성적 향상에는 유의한 영향을 미치는 변수가 아니었다(p=0.325). 연구결과 학생들은 감염병의 감염위험으로 인해 비대면 강의에 대한 요구도가 높았지만, 비대면 강의 방법에 대해서는 녹화된 강의내용보다는 실시간으로 문제를 해결할 수 있는 강의 방법을 희망하는 것으로 나타났다. 이런 학생들의 요구사항을 반영하여 교수자는 비대면 강의 교안을 개발할 것으로 생각된다.

• 한국해양공학회지
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• 제23권4호
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• pp.69-77
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• 2009

Structural analysis of a brake shoe for commercial vehicle was performed using finite element method. Since the strength of a brake shoe is affected by the magnitude and distribution shape of the contact pressure with the drum, the contact pressure between the shoe friction material and drum was calculated using a 2-Dimensional non-linear contact analysis in a state. And the brake was actuated by input air pressure and the drum of it was calculated both stationary and dynamic based on forced torque applied to the drum during the static state analysis. The results of the above analysis were then used as the load boundary conditions for a 3-Dimensional shoe model analysis to determine the maximum strain on the shoes. In the analysis model, the values of tensile test were used for the material properties of the brake shoes and drum, while the values of compression test were used for the friction material. We assumed it as linear variation, even though the properties of friction material were actually non-linear. The experiments were carried out under the same analysis conditions used for fatigue test and under the same brake system which equipped with a brake drum based on the actual axle state in a vehicle. The strains were measured at the same locations where the analysis was performed on the shoes. The obtained results of the experiment matched well with those from the analysis. Consequently, the model used in this study was able to determine the stress at the maximum air pressure at the braking system, thereby a modified shoe model in facilitating was satisfied with the required endurance strength in the vehicle.

• 대한전자공학회논문지SD
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• 제39권12호
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• pp.1001-1007
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• 2002

된 논문에서는 펜타센을 활성층으로 사용하는 유기박막트랜지스터(OTFT)의 펜타센의 두께, 그리고 소오스 및 드레인 전극의 위치에 따른 소자의 성능 변화에 대하여 연구하였다. 펜타센 박막의 두께가 증가하면 그레인 상태가 박막상태에서 벌크상태로 변화하면서 결정도가 악화되어 성능이 열화하였고, 소오스와 드레인 전극을 펜타센 위에 제작한 소자의 경우 접촉저항은 감소하였으나 누설전류가 증가하여 전류 점멸비가 감소하였다. 그러므로, 펜타센의 두께는, 300Å∼700Å 내외, 그리고 전극은 펜타센 아래에 위치하는 것이 적합한 것으로 확인되었다.

• 대한기계학회논문집
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• 제13권3호
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• pp.353-361
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• 1989

본 논문에서는 유한 요소법을 이용하여 접촉을 고려한 나사 체결 문제를 해석하고 여러 다른 체결조건이 각 나사산에 걸리는 하중 분담율에 미치는 영향을 살펴보고, 이 하중 분담율이 보다 균일화 될 수 있는 체결 조건을 찾고, 또 그때의 응력 분포를 살펴보는 것을 목적으로 한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.138-143
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• 2005

Finite Element analysis is widely applied to elevated temperature forging processes and shows a lot of information of plastic deformation such as strain, stress, defects, damages and temperature distributions. In highly elevated temperature deformation processes, temperature of material and tool have significant influence on tool life, deformation conditions and productivities. To predict temperature related properties accurately, adequate coefficients of not only contact heat transfer between material and dies but also convection heat transfer due to coolants are required. In most F.E analysis, too higher value of contact heat transfer coefficient is usually applied to get acceptable temperature distribution of tool. For contact heat transfer coefficients between die and workpiece, accurate values were evaluated with different pressure and lubricants conditions. But convection heat transfer coefficients have not been investigated for forging lubricants. In this research, convection heat transfer coefficients for cooling by emulsion lubricants are suggested by experiment and Inverse method. To verify acquired convection and contact heat transfer coefficients, tool temperature was measured for the comparison between measured tool temperature and analysis results. To increase analysis accuracy, repeated analysis scheme was applied till temperature of the tool got to be in the steady-state conditions. Verification of heat transfer coefficients both contact and convection heat transfer coefficients was proven with good accordance between measurement and analysis.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1314-1321
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• 2019

In case of multiple failure scenario, such as LOCA with ECCS failure, the decay heat continues to raise the reactor core temperature, eventually leading to the core voiding. In such scenario the convective heat transfer becomes poor and the majority of the heat transfer from fuel bundle takes place by radiation mode. During this abnormal working condition, if the channel pressure is less than 1 MPa, the PT sags and come in contact with the CT. This results in high rate of heat transfer from contact location to moderator. The present paper aims to capture the temperature profile over a simulated nuclear channel during such scenario at a steady state temperature of $600^{\circ}C$ (Centre pin) at two different configurations of PT i.e. PT concentric with CT and PT contact with CT. The results showed that the bottom nodes of all the components (Fuel bundle, PT and CT) of the simulated channel was greatly influenced by the PT/CT contact. Moreover, higher temperature were observed at top nodes of the PT and outer pins of the fuel bundle. However, no significant variation in temperatures were obtained in fuel bundle and CT in concentric condition.

• 에너지공학
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• 제8권2호
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• pp.272-278
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• 1999

본 연구에서는 지름 30mm, 길이 45mm인 brass와 aluminium 원통 실린더의 접촉면이 ⅰ) 진공 상태에 있을 때 , ⅱ) silicone grease를 충전하였을 때 , ⅲ) silicone grease와 aluminium 분말 (#325) 혼합물을 충전하였을 때의 열접촉저항을 측정하였고, 그 결과를 Fouche 의 해석 모델과 비교하였다. 진공상태에서 비접촉면의 열접촉저항은 표면의 가공 상태에 따라 (2~100)$\times$$10^{-5}$($m^2$$^{\circ}C$/W)의 분포를 나타내었고 접촉 표면을 연마하였을 때에는 거친 표면에 비하여 약 30~50%의 열접촉저항저감을 나타내었다. 그러나, silicone grease를 충전했을 때에는 열접촉저항 값이 약 5~10정도 감소하는 경향을 나타내었다. Fouche 모델을 이용한 해석 결과는 silicone grease로 충전한 접촉면에 대해서 각 10~30%범위에서 아주 잘 일치하였다.

• 터널과지하공간
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• 제26권5호
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• pp.409-417
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• 2016

본 전통석유자원을 대체할 수 있는 석유자원으로 부상하고 있는 셰일가스가 부존된 셰일층은 낮은 투과성을 가지고 있어 생산성을 향상시키기 위해 수압파쇄법이 적용된다. 본 연구는 일반 시추공과 나선형 홈을 가지는 시추공을 모사한 축소 모형 시험체에 대해 실내수압파쇄 시험을 실행하고 초기파쇄압과 유체접촉상태를 비교 분석하여 공벽형상에 따른 수압파쇄결과를 알아보았다. 또 그 결과를 3차원 개별요소 프로그램인 3DEC을 이용한 수치해석 모델링 값과 비교하였으며, 선행연구 자료와 비교하여 신뢰성 있는 결과를 도출하고자 하였다. 실험결과 고압수의 접촉면적보다는 유도홈의 형태에 의한 응력집중의 효과가 수압파쇄에 더욱 효율적이였다. 따라서 고압수의 응력집중을 높일 수 있는 인공적인 유도홈을 만들 시 적은 수압으로 큰 파쇄효과를 나타낼 수 있을것으로 생각된다.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1638-1645
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• 2006

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of $1{\sim}2mm/sec$ and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.