• Structural Engineering and Mechanics
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• 제62권5호
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• pp.595-606
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• 2017

During their life span, post-tensioned concrete structures may be exposed to thermal loads. Therefore, there has been a growing interest in research on the advanced analysis and design of post-tensioned concrete slabs subjected to thermal loads. This paper investigates the structural behaviour of post-tensioned one-way spanning concrete slabs. A nonlinear finite element model for the analysis of post- tensioned unbonded and bonded concrete slabs at elevated temperatures was developed. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The load-deflection behaviour, load-force behaviour in the tendon, and the failure modes are presented. The numerical analysis was conducted by the finite element ANSYS software and was carried out on two different one-way concrete slabs chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned one-way concrete slab. These parameters include the effect of tendon bonding, the effect of thermal loading and the effect of tendon profile. Comparison between uniform thermal loading and nonuniform thermal loading showed that restrained post tensioned slab with bottom surface hotter has smaller failure load capacity.

• 전자공학회논문지A
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• 제33A권10호
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• pp.107-114
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• 1996

Monte carlo method is especially a useful method for the analysis of thermal noise of semiconductor devices since the time dependence of microscopic details is simulated directly. Recently, a mthod for the calculation of the instantaneous currents of 2-dimensional devices, which is numerically more accurate than the conventional method, has been proposed using the generalized ramo-shockley theorem. Using this mehtod we investage the validity of the existing thermal noise theories of field-effect transistors. First, the 1-dimensional analysis of thermal noise theories of field-effect transistors. First, the 1-dimensional analysis of thermal noise theories of field-effect transistors. First, the 1-dimensional analysis of thermal noise using ramo-shockley theorem is shown to be applicable to 2 dimensional devices if the frequency of interest is low enough. The correlation between electrons in different regions of th echannel is shown not to be negligible. And we also obtian the spatial map of the noise in the channel region. By doing so, we show that the steady state nyquist theorem is the correct theory rather than the theory by van der ziel et.al.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.275-279
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• 1996

In this study, the effect of external restraint on the thermal stresses and thermal cracking mode in mass concrete are analysed using the two major factors affecting external restraint such as the ratio of width go height of the placed structure (L/H) and the elastic modulus of base structure (E). For this parametric study, many cases with different values of L/H and Er are analysed by the FEM program and the co-relationship of the those major factors is examined. To evaluate the effect of external restraint on the thermal behavior of placing structure, internal restraint stress caused by temperature difference is subtracted from total thermal stress. In the case of small value of L/H or Er, it shows as internally restricted mode indicating maximum tensile stress in surface at early age, and the external restraint makes the possibility of thermal cracking higher. However, in the case of the large values of L/H and Er, the crack index at center is smaller than at surface due to the effect of external restraint. Thus, the initial location of the thermal crack is shifted from the surface to the center and the resulting crack is formed at later age.

• 한국응용과학기술학회지
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• 제27권4호
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• pp.552-558
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• 2010

Zinc soap and Zn/Ba mixed metal soap were synthesized and PVC plastisol with mixed metal soap and various costabilizers were also synthesized with good structures and characterized by IR and $^1H$-NMR. The IR spectrums and $^1H$-NMR spectrums of the synthesized soaps were in very good accordance with the structures proposed by earlier workers. In using phosphite as a costabilizer, TIDP phosphite was shown to be the excellent thermal stabilization effect at the low temperature and TNPP phosphite was shown to be the excellent thermal stabilization effect at the high temperature. In case of antioxidant, it was revealed that antioxidant was not effective in the low temperature thermal stabilization effect while highly effective in the high temperature thermal stability. $NaClO_4$ solution with sorbitol solvent had the best thermal stabilization effect among $NaClO_4$ solution series at low and high temperature.

• 한국신뢰성학회지:신뢰성응용연구
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• 제6권2호
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• pp.173-186
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• 2006

This paper presents a study on the failure mechanism for optical engine of Projection TV. The lenses of which optical engine composes are failed by various environmental conditions, that is, thermal effect, moisture effect, mechanical shock or chemical effect. By surveying on actual TV working condition, the major factor of failure was turned out the thermal effect. Because the actual surface temperature of optical engine rose at max. $51^{\circ}C$ during it worked, the relative humidity around optical engine was kept at less than 20% that is difficult to do chemical reaction with humidity. Therefore we can make a conclusion that the major failure of optical engine resulted from thermal effect.

• 한국가시화정보학회지
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• 제18권2호
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• pp.28-34
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• 2020

In this study, we numerically investigated the thermal stratification in solar seasonal thermal storage tanks. The vertical in/out flows were unsuitable for the thermal stratification in a large scale. The effect of an aspect ratio (AR) on the thermal stratification was investigated. When AR was less than 2, water adheres and flows along the upper wall due to buoyance and the surface effect. Thereafter, hot water flows down and a large scale vortex occurs in entire tank. For high AR, jet flows ejected from the inlet pipe impinges to the opposite wall and splits. The divided flows create two vortex flows in the upper and lower regions. These different flows strongly influence temperature and thermal stratification. The thermal stratification was evaluated in terms of the thermocline thickness and degree of stratification. Compared to ARs, the maximum degree of stratification was obtained with AR of 5 having the minimum thermocline thickness.

• 터널과지하공간
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• 제12권3호
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• pp.220-228
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• 2002

절리암반에서의 열유동을 수치해석적으로 분석하였다. 1차원 모델 해석을 통하여 한 조의 절리군이 열전도에 미치는 영향을 비교 분석하고, 이론해와 비교하였다. 절리 내에 물이 전혀 없는 경우, 절리는 열 차단제의 역할을 하며 정상상태에서도 온도의 불연속이 관찰되었다. 따라서 암반 내 존재하는 절리가 완전 건조상태인 경우에는 개별적인 절리의 열차단 효과를 일일이 고려하여야 정확한 결과를 얻을 수 있다 그러나 절리 내에 물이 부분적으로 혹은 완전히 포화된 경우에는 열차단 효과가 현저히 줄어들어 온도 분포에 미치는 영향이 현저히 감소하였다. 따라서 절리 암반을 통한 열전도는 암반을 무결암의 열적 성질과 불연속면의 열적 성질을 포함한 열적 이방성 연속체로 가정함으로써 가능하다 할 수 있다. 절리의 포화 정도가 증가할수록 절리가 열유동에 미치는 영향이 감소하므로 암반의 열전달 특성은 등방에 가까워지며, 따라서 복잡한 모델을 이용한 해석보다는 현지 암반의 열물성을 정확히 측정하는 것이 더욱 중요함을 알 수 있었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 춘계학술대회 논문집
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• pp.439-444
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• 2004

The important problem in high speed spindle is to reduce and minimize the thermal effect by motor and ball bearings. In this study. the effects of bearing preload and cooling for high speed spindle with high frequency motor are investigated. A high speed spindle is composed of angular contact ball bearings, high frequency motor, grease lubrication, oil jacket cooling, and so on. Heat generation of the bearing and the high frequency motor are estimated from the theoretical and experimental data. The thermal analyses of high speed spindle to minimize the thermal effect and maximize the cooling effect are carried out under the various cooling conditions and preload. Method of variable bearing preload and cooling can be useful to design the high speed motor spindle. The results show that the optimal preload and cooling are very effective to minimize the thermal displacement by motor and ball bearing.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.41-46
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• 2003

The important problem in high speed spindles is to reduce and minimize the thermal effect by motor and bail bearings. Thermal characteristics according to the bearing pre-load and cooling condition are studied for the test spindl with grease lubrication and high frequency motor. Bearing and motor we main heat generation, and heat generation by ball bearings as a function of load, viscosity and gyroscopic moment effect are considered. Temperature distribution and thermal displacement according to the speed of spindle are measured by thermocouple and gap sensor. The results show that the fitting pre-load and cooling temperature are very effective to minimize the thermal effect by motor an ball bearings.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.428-432
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• 2004

The important problem in the high speed spindles is to reduce and minimize the thermal effect by the motor and ball bearings. Thermal characteristics according to the bearing preload and hollow shaft cooling are studied for the test spindle with the oil mist lubrication and high frequency motor. Bearings and motor e main heat generation, and heat generation by ball bearings as a function of load, viscosity and gyroscopic moment effect are considered. Temperature distribution and thermal displacement according to the speed of spindle are measured by thermocouple and gap sensor. The results show that the fitting preload and hollow haft cooling are very effective to minimize the thermal effect by the motor and ball bearings.