• 한국전산유체공학회지
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• 제15권2호
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• pp.28-34
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• 2010

Conductive and radiative thermal model configurations of an imager of a geostationary satellite are presented. A two-plane method is introduced for three dimensional conductive coupling which is not able to be treated by thin shell plate thermal modeling technique. Especially the two-plane method is applied to massive matters and PIP(Payload Interface Plate) in the imager model. Some massive matters in the thermal model are modified by adequate correction factors or equivalent thickness in order to obtain the numerical results of thermal modeling to be consistent with the analytic model. More detailed nodal breakdown is specially employed to the object which has the rapid temperature gradient expected by a rule of thumb. This detailed thermal model of the imager is supposed to be used for analyses and test predictions, and be correlated with the thermal vacuum test results before final in-flight predictions.

• 한국결정성장학회지
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• 제9권2호
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• pp.240-244
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• 1999

화학기상증착법(CVD)을 사용하여 graphite 기판 위에 단층의 SiC와 SiC/C 경사기능층을 증착시켰다. 먼저 상업적인 전산 구조 해석 프로그램을 사용하여 열충격하에 있는 재료층 내부의 온도 분포 및 열응력 분포를 계산하였고, 계산에 의해 설계, 제작된 경사기능층 시편들의 열특성을 조사하였다. 열충격 시험결과, 경사기능층 시편들이 계면에서 매우 효율적인 열응력 이완특성을 나타내는 것을 알 수 있었고, $\Delta$T=1600K의 열충격에도 변형이 없음을 알 수 있었다.

• 한국전산유체공학회지
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• 제12권3호
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• pp.62-68
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• 2007

A conceptual thermal design is performed for the optical payload system of a geostationary satellite. The optical payload considered in this paper is GOCI(Geostationary Ocean Color Imager) of COMS of Korea. The radiative thermal control system is employed in order to expect a small thermal gradient in the telescope structure of GOCl. Two design margins are applied to the dedicated radiator dimensioning, and three kinds of configuration to the heater power sizing. A Monte-Carlo ray tracing method and a network analysis method are utilized to calculate radiative couplings and thermal responses respectively. At the level of conceptual design, sizing thresholds are presented for the radiator and heater on the purpose of determining the mass and power budget of the spacecraft.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.221-225
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• 2004

Evaluation of turbulence models is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor by applying them to the experiment conducted at JNC. The turbulence models tested in the present study are the two-layer model, the $\kappa-\omega$ model, the v2-f model and the low-Reynolds number differential stress-flux model. When the algebraic flux model or differential flux model are used for treating the turbulent heat flux, there exist little differences between turbulence models in predicting the temporal variation of temperature. However, the v2-f model and the low-Reynolds number differential stress-flux model better predict the steep gradient o( temperature at the interface of thermal stratification, and only the v2-f model predicts properly the oscillation of temperature. The LES Is needed for a better prediction of the amplitude and frequency of the temperature fluctuation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.132-137
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• 2000

A complete theoretical treatment of the photothermal displacement technique has been performed for thermal diffusivity measurement in solid materials. The influence of parameters - radius and modulation frequency of pump beam and thickness of material - on the phase lag was studied. The phase decreases up to a certain position, then starts to increase and does have an asymptotic value. The position, where phase has the minimum value, is a function of thermal diffusion length thickness of sample, and radius of pump beam. A new method based on minimum phase lag is described to determine the thermal diffusivity of solid material.

• Nuclear Engineering and Technology
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• 제33권2호
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• pp.192-200
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• 2001

Hydride blisters were formed on the outer surface of Zr-2.5Nb pressure tube by a non- uniform steady thermal diffusion process. A thermal gradient was applied to the pressure tube with a heat bath kept at a temperature of 415$^{\circ}C$ and an aluminum cold finger cooled with flowing water of 15$^{\circ}C$. Optical microscopy and tree-dimensional laser profilometry were used to characterize the hydride blisters with different hydrogen concentrations and thermal diffusion time. Hydride blisters were expected to start at a hydrogen concentration of 30 - 70 ppm and a thermal diffusion time of 4 - 6$\times$10$^{5}$ sec. The hydride blister size increases with higher hydrogen concentrations and longer thermal diffusion time . Some of the samples revealed cracks on the hydride blisters. The ratio of hydride blister depth to height was estimated as approximately 8: 1.

• Structural Engineering and Mechanics
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• 제41권6호
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• pp.775-789
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• 2012

This paper focuses on post-buckling analysis of functionally graded Timoshenko beam subjected to thermal loading by using the total Lagrangian Timoshenko beam element approximation. Material properties of the beam change in the thickness direction according to a power-law function. The beam is clamped at both ends. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of functionally graded Timoshenko beams under thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, with the effects of material gradient property and thermal load, the relationships between deflections, end constraint forces, thermal buckling configuration and stress distributions through the thickness of the beams are illustrated in detail in post-buckling case.

• 한국표면공학회지
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• 제57권3호
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• pp.155-164
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• 2024

Physical properties of carbon nanomaterials are dependent on their nanostructures and they are modified by diverse synthesis methods. Among them, thermal plasma method stands out for synthesizing carbon nanomaterials by controlling chemical and physical reactions through various design and operating conditions such as plasma torch type, plasma gas composition, power capacity, raw material injection rate, quenching rate, kinds of precursors, and so on. The method enables the production of carbon nanomaterials with various nanostructures and characteristics. The high-energy integration at high-temperature region thermal plasma to the precursor is possible to completely vaporize precursors, and the vaporized materials are rapidly condensed to the nanomaterials due to the rapid quenching rate by sharp temperature gradient. The synthesized nanomaterials are averagely in several nanometers to 100 nm scale. Especially, the thermal plasma was validated to synthesize low-dimensional carbon nanomaterials, carbon nanotubes and graphene, which hold immense promise for future applications.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.84-89
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• 2003

Fuzzy controller is one of the succeed controller used in the process control in case of model uncertainties. But it my be difficult to fuzzy controller to articulate the accumulated knowledge to encompass all circumstance. Hence, it is essential to provide a tuning capability. There are many parameters in fuzzy controller can be adapted, scale factor tuning of normalized fuzzy controller is one of the adaptation parameter. Two adaptation methods are implemented in this work on an experimental thermal process, which simulate heating process in liquefied petroleum gases (LPG) recovery process in one of petrochemical industries: Gradient decent (GD) adaptation method; supervisory fuzzy controller. A comparison between the two methods is discussed.

• International Journal of Fluid Machinery and Systems
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• 제2권1호
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• pp.55-60
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• 2009

The present study investigated temperature and thermal stress distributions in a film cooling system with normal injection cooling flow. 3D-numerical simulations using the FEM commercial code ANSYS were conducted to calculate distributions of temperature and thermal stresses. In the simulations, the surface boundary conditions used the surface heat transfer coefficients and adiabatic wall temperature which were converted from the Sherwood numbers and impermeable wall effectiveness obtained from previous mass transfer experiments. As a result, the temperature gradients, in contrast to the adiabatic wall temperature, were generated by conduction between the hot and cold regions in the film cooling system. The gradient magnitudes were about 10~20K in the y-axis (spanwise) direction and about 50~60K in the x-axis (streamwise) direction. The high thermal stresses resulting from this temperature distribution appeared in the side regions of holes. These locations were similar to those of thermal cracks in actual gas turbines. Thus, this thermal analysis can apply to a thermal design of film cooling holes to prevent or reduce thermal stresses.