• 한국지반공학회논문집
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• 제32권7호
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• pp.5-14
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• 2016

최근 들어 경제적이고 친환경적인 에너지 활용을 위하여 지열에너지의 필요성이 점차 증대되고 있다. 특히 지열히트펌프 시스템(geothermal heat pump system)으로 불리는 지열 냉난방 시스템의 적용성이 계속 확대되고 있다. 이러한 지열히트펌프 시스템에서 지반의 열전도도와 열확산계수와 같은 지중 열물성은 설계 과정에서 매우 중요한 변수이기에 현장 열응답 시험(thermal response test)을 통해 지반의 열전도도를 산출해야 한다. 본 논문에서는 U와 2U 타입의 지중 열교환기를 매립지 지반에 설치한 후 48시간 동안 현장 열응답 시험을 수행하였으며 지반의 열전도도 뿐만 아니라 지반의 열확산계수를 비선형 회귀분석을 통해 산정할 수 있는 방안을 제시하였다. 또한 지중 열교환기가 설치된 지반의 시료를 채취하여 실내 열물성 실험을 수행하였으며 이를 현장 열응답 시험을 통해 도출된 지반의 열전도도 및 열확산계수 값과 비교하였다.

• Structural Engineering and Mechanics
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• 제48권4호
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• pp.547-567
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• 2013

Nonlinear behavior of functionally graded material (FGM) plates under thermal loads is investigated here using an efficient sinusoidal shear deformation theory. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the sinusoidal distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed efficient sinusoidal shear deformation theory contains only four unknowns. The material is graded in the thickness direction and a simple power law based on the rule of mixture is used to estimate the effective material properties. The neutral surface position for such FGM plates is determined and the sinusoidal shear deformation theory based on exact neutral surface position is employed here. There is no stretching-bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The non-linear strain-displacement relations are also taken into consideration. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. Closed-form solutions are presented to calculate the critical buckling temperature, which are useful for engineers in design. Numerical results are presented for the present efficient sinusoidal shear deformation theory, demonstrating its importance and accuracy in comparison to other theories.

• 대한기계학회논문집B
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• 제39권6호
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• pp.505-511
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• 2015

고체 산화물 연료전지는 $800{\sim}1000^{\circ}C$의 고온에서 작동한다. 고온 작동은 효율에 유리하지만 재료 요구 조건, 신뢰성, 열팽창 문제 등이 발생하여 온도 제어가 중요하다. 본 연구에서는 연료전지 시스템의 열관리를 위한 상태 공간 제어기를 설계하고 응답 특성을 확인하였다. 연료전지 스택과 열관리 핵심부품인 촉매연소기는 집중 용량법을 이용한 과도 응답 모델을 개발하였고, 구성품과 통합하여 정적 운전 특성을 확인하였다. 개발된 비선형 시스템을 정격 운전 조건에서 다중 입력과 출력이 가능한 상태 공간 식으로 선형화하였다. 부하에 따라 응답특성이 현저하게 달라지는 특성을 제어하기 위해 LQR 제어기를 설계하여 궤환 제어 시스템의 온도를 제어하였다. 상태 궤환 제어기가 적어도 두 개의 제어 게인을 가지고 운전 영역에 따른 응답을 보여줄 때, 원하는 온도 응답을 나타냄을 확인하였다.

• 대한건축학회논문집:구조계
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• 제33권12호
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• pp.91-98
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• 2017

In this study, the effect of window installation position in the residential building with the external insulation was numerically investigated in terms of insulation performance and heating/cooling energy consumption. For different window positions, 2-D heat transfer simulation was conducted to deduce the linear thermal transmittance, which was inputted to the dynamic energy simulation in order to analyze heating/cooling energy consumption. Simulation results showed that the linear thermal transmittance ranges from 0.05 W/mK to 0.7 W/mK, and is reduced as the window is installed near the external finish line. Indoor surface temperature and TDR analysis showed that the condensation risk is the lowest when the window is installed at the middle of the insulation and wall structure. It was also found that the window installation near the external finish can reduce the annual heating/cooling energy consumption by 12~16%, compared with the window installation near the interior finish. Although the window installation near the external finish can achieve the lowest heating/cooling energy consumption, it might lead to increased condensation risks unless additional insulation is applied. Thus, it can be concluded that the window should be installed near the insulation-wall structure junction, in consideration of the overall performance including energy consumption, condensation prevention and constructability.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.60.2-60.2
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• 2011

A study of the non-linear optical properties of nanocrystal-Si embedded in SiO2 has been performed by using the z-scan method in the nanosecond and femtosecond ranges. Substoichiometric SiOx films were grown by plasma-enhanced chemical-vapor deposition(PECVD) on silica substrates for Si excesses up to 24 at/%. An annealing at $1250^{\circ}C$ for 1 hour was performed in order to precipitate nanocrystal-Si, as shown by EFTEM images. Z-scan results have shown that, by using 5-ns pulses, the non-linear process is ruled by thermal effects and only a negative contribution can be observed in the non-linear refractive index, with typical values around $-10-10cm^2/W$. On the other hand, femtosecond excitation has revealed a pure electronic contribution to the nonlinear refractive index, obtaining values in the order of 10-12 cm2/W. Simulations of heat propagation have shown that the onset of the temperature rise is delayed more than half pulse-width respect to the starting edge of the excitation. A maximum temperature increase of ${\Delta}T=123.1^{\circ}C$ has been found after 3.5ns of the laser pulse maximum. In order to minimize the thermal contribution to the z-scan transmittance and extract the electronic part, the sample response has been analyzed during the first few nanoseconds. By this method we found a reduction of 20% in the thermal effects. So that, shorter pulses have to be used obtain just pure electronic nonlinearities.

• Advances in aircraft and spacecraft science
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• 제7권4호
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• pp.335-351
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• 2020

Thermal buckling of functionally graded sandwich cylindrical shells is presented in this study. Material properties and thermal expansion coefficient of FGM layers are assumed to vary continuously through the thickness according to a sigmoid function and simple power-law distribution in terms of the volume fractions of the constituents. Equilibrium and stability equations of FGM sandwich cylindrical shells with simply supported boundary conditions are derived according to the Donnell theory. The influences of cylindrical shell geometry and the gradient index on the critical buckling temperature of several kinds of FGM sandwich cylindrical shells are investigated. The thermal loads are assumed to be uniform, linear and nonlinear distribution across the thickness direction. An exact simple form of nonlinear temperature rise through its thickness taking into account the thermal conductivity and the inhomogeneity parameter is presented.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(3)
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• pp.265-270
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• 1996

The temperature distribution in the pellet was obtained from beginning the general heat conduction equation. The thermal conductivity of pellet used the SIMFUEL data that made clear the effect of burnup on the thermal conductivity degradation. Since the pellet rim acts as the thermal barrier to heat flow. the pellet was subdivided into several rings in which the outer ring was adjusted to play almost the same role as the rim. The local burup in each ring except the outer ring was calculated from the power depression factor based on FASER results. whereas the rim burnup at the outer ring was achieved by the pellet averaged burnup based on the empirical relation. The rim changed to the equivalent Xe film so the predicted temperature shooed the thermal jump across the rim. The observed temperature profiles depended on linear heat generation rate. fuel burnup. and power depression factor. The thermal conductivity degradation modelling can be applied to the fuel performance code to high burnup fuel,

• 대한기계학회논문집
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• 제18권7호
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• pp.1664-1673
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• 1994

As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.195-198
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• 2000

It can be acquired the high effective productivity through of high speed, precision of machine tools, and then, machine tools will be got a competitive power. Industrially advanced countries already developed that the high speed feed is 60m/min using the high speed ball screw. Also, a lot of problems have happened the feed drive system. It is necessary to study about the characteristics of thermal deformation played a more critical role than static stiffness and dynamic rigidity in controlling the level of machining accuracy. In spite of the improving the thermal deformation characteristics of machine tools at the design stage, there are always some residual errors that have to be compensated for during machining. In this study, thermal deformation error automated compensation device with multiple linear regression is proposed that thermal deformation error can be eliminated at the machining stage. The developed device has been practically applied to the feed drive unit.

• 한국의류학회지
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• 제22권7호
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• pp.816-825
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• 1998

This study surveys the thermal property and air permeability to the weight reduction rate of PET fabrics. For this purpose, 12 kinds of satin and 18 kinds of plain weave fabrics are prepared with change of the physical properties such as weft yarn count, t.p.m. and density. The weight reduction rate was 0%, 12%, 25% and 30%. The warm/cool feeling(Qmax), thermal insulating value(T.I.V.) and thermal conductivity(K) were measured by KES-F7 System and discussed in relation with the weight reduction rate, weft yarn linear density, t.p.m., weft density of fabric and weave structure.