• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.2099-2106
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• 2003

In this paper, a novel fast response NDIR analyzer (FRNDIR), which uses an electrically pulsed semiconductor emitter and dual type PbSe detector for the PPM-level detection of carbon dioxide (CO$_2$) at a wavelength of 4.28 $\mu\textrm{m}$, is described. Modulation of conventional NDIR energy typically occurs at 1 to 20 Hz. To achieve real time high-speed measurement, the new analyzer employs a semiconductor light emitter that can be modulated by electrical chopping. Updated measurements are obtained every one millisecond. The detector has two independent lead selenide (PbSe) with IR band pass filters. Both the emitter accuracy and the detector sensitivity are increased by thermoelectric cooling of up to -20 degrees C in all semiconductor devices. Here we report the use of semiconductor devices to achieve improved performance such that these devices have potential application to CO$_2$ gas measurement and, in particular, the measurement of fast response CO$_2$ concentration at millisecond level.

• Current Optics and Photonics
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• v.7 no.3
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• pp.254-262
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• 2023

Novel thermo-optically focus-switchable Fresnel zone plates based on phase-change metafilms are designed and analyzed at a visible wavelength (660 nm). By virtue of the large thermo-optic response of vanadium dioxide (VO₂) thin film, a phase-change material, four different plasmonic phase-change absorbers are numerically designed as actively tunable Gires-Tournois Al-VO₂ metafilms in two and three dimensions. The designed phase-change metafilm unit cells are used as the building blocks of actively focus-switchable Fresnel zone plates with strong focus switching contrast (40%, 83%) and high numerical apertures (1.52, 1.70). The Fresnel zone plates designed in two and three dimensions work as cylindrical and spherical lenses in reflection type, respectively. The coupling between the thermo-optic effect of VO₂ and localized plasmonic resonances in the Al nanostructures offer a large degree of freedom in design and high-contrast focus-switching performance based on largely tunable absorption resonances. The proposed method may have great potential in photothermal and electrothermal active optical devices for nonlinear optics, microscopy, 3D scanning, optical trapping, and holographic displays over a wide spectral range including the visible and infrared regimes.

• Journal of Korean Society of Steel Construction
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• v.21 no.6
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• pp.609-618
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• 2009

This paper proposes a versatile formula which can be used to evaluate the fire resistant time of steel beams under various design conditions. Towards this end, the key parameters which affect the fire performance of steel beams were first determined through thermo-mechanical considerations, and classified into two groups: structural parameters and thermal parameters. Then the degree of influence of each parameter on the fire performance was investigated through a fully coupled thermo-mechanical analysis up to the occurrence of run-away deflection. The accuracy of the numerical model used was verified using an available full-scale fire test before conducting an extensive parametric analysis. Multiple linear regression analysis was performed to obtain the formula which can be used to predict the fire resistance time of steel beams under various design conditions. The statistical analysis showed that the proposed formula is very robust. The application of the formula in practical fire design under the current code was illustrated in detail. The economy and other advantages of the proposed formula were clearly shown.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2540-2545
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• 2007

A computational study of BLDC motor is presented to elucidate thermo-flow characteristics in winding and bearing with heat generation. Rotation of rotor and blades drives influx of ambient air into the rotor inlet and the inflow rates are predicted more at the front-side inlet than at the rear-side, which can be ascribed to the different pressure distribution. Recirculation zone appears in the tiny interfaces between windings, however, showing the enhanced cooling performance due to the higher velocity distribution near the rotor wall. In contrast, flow separation and incline angle of bearing groove, and relatively slower velocity distribution cause poor cooling performance and therefore the redesign of the bearing groove is significantly required.

• Composites Research
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• v.36 no.2
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• pp.117-125
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• 2023

This paper proposes a new finite element formulation based on enhanced first-order shear deformation theory including the transverse normal strain effect via the mixed formulation (EFSDTM-TN) for the effective thermo-mechanical analysis of laminated composite structures. The main objective of the EFSDTM-TN is to provide an accurate and efficient solution in describing the thermo-mechanical behavior of laminated composite structures by systematically establishing the relationship between two independent fields (displacement and transverse stress fields) via the mixed formulation. Another key feature is to consider the thermal strain effect without additional unknown variables by introducing a refined transverse displacement field. In the finite element formulation, an eight-node isoparametric plate element is newly developed to implement the advantage of the EFSDTM-TN. Numerical solutions for the thermo-mechanical behavior of laminated composite structures are compared with those available in the open literature to demonstrate the numerical performance of the proposed finite element model.

• Transactions of Materials Processing
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• v.20 no.7
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• pp.473-478
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• 2011

In this study, the performance of a thermo siphon type radiator made of copper for LED lighting system was evaluated by using an inverse heat transfer method. Heating experiments and finite element heat transfer analysis were conducted for three different cases. The data obtained from experiments were compared with the analysis results. Based on the data obtained from experiments, the inverse heat transfer method was used in order to evaluate the heat transfer coefficient. First, the heat transfer analysis was conducted for non-vacuum state, without the refrigerant. The evaluated heat transfer coefficient on the radiator surface was 40W/$m^2^{\circ}C$. Second, the heat transfer analysis was conducted for non-vacuum state, with the refrigerant, resulting in the heat transfer coefficient of 95W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the third case, the evaluated heat transfer coefficients were 140W/$m^2^{\circ}C$ for the radiator body, 5W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant for the rising position of radiator pipe, 35W/$m^2^{\circ}C$. Third, the heat transfer analysis was conducted for vacuum state, with refrigerant. For the highest position of radiator pipe, and 120W/$m^2^{\circ}C$ for the downturn position of radiator pipe. As a result of inverse heat transfer analysis, it was confirmed that the thermal performance of the current radiator was best in the case of the vacuum state using the refrigerant.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.39-52
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• 2009

Theory-based models and high performance simulations are briefly reviewed starting with atomistic methods, such as Electronic Structure calculations, Molecular Dynamics, and Monte Carlo, continuing with meso-scale methods, such as Dislocation Dynamics and Phase Field, and ending with continuum methods that include Finite Element and Finite Volume. Special attention is paid to relating thermo-mechanical and chemical properties of the fuel to reactor parameters. By inserting atomistic models of point defects into continuum thermo-chemical calculations, a model of oxygen diffusivity in $UO_{2+x}$ is developed and used to predict point defect concentrations, oxygen diffusivity, and fuel stoichiometry at various temperatures and oxygen pressures. The simulations of coupled heat transfer and species diffusion demonstrate that including the dependence of thermal conductivity and density on composition can lead to changes in the calculated centerline temperature and thermal expansion displacements that exceed 5%. A review of advanced nuclear fuel performance codes reveals that the many codes are too dedicated to specific fuel forms and make excessive use of empirical correlations in describing properties of materials. The paper ends with a review of international collaborations and a list of lessons learned that includes the importance of education in creating a large pool of experts to cover all necessary theoretical, experimental, and computational tasks.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.519-536
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• 2015

On-line electric vehicle (OLEV) is a new eco-friendly transportation system that collects electricity from a power cable buried beneath the road surface, allowing the system to resolve various problems associated with batteries in electric vehicles. This paper presents a finite element (FE) based thermo-mechanical analysis of precast concrete structures that are utilized in the OLEV system. An experimental study is also conducted to identify materials used for a joint filler, and the observed experimental results are applied to the FE analysis. Traffic loading and boundary conditions are modeled in accordance with the related standards and environmental characteristics of a road system. A series of structural analyses concerning various test scenarios are conducted to investigate the sensitivity of design parameters and to evaluate the structural performance of the road system.

• International Journal of Industrial Entomology and Biomaterials
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• v.2 no.2
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• pp.111-117
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• 2001

Screening of fifteen bivoltine silkworm breeds of Bombyx mori Linn at a temperature of $31{\pm}1^{\circ}C$ and relative humidity of 85${\pm}$5% resulted in the identification of eight thermo-tolerant breeds. The survival and cocoon shell ratio of the tolerant breeds ranged from 72.7 to 78.7% and 20.0 to 20.1% respectively. The tolerant breeds comprised of four oval breeds and four dumb-bell breeds. Eight foundation crosses prepared by crossing the oval and dumb-bell parents among themselves were screened at a temperature of $31{\pm}1^{\circ}C$ and relative humidity of 85{\pm}5%. The performance of the foundation crosses on 11 economic characters were analysed by employing Multipie Trait Evaluation Index method. Four foundation crosses which scored average index value > 50 were selected as breeding parents and breeding initiated for the evolution of thermo-tolerant bivoltine silkworm breeds. The methodology and the results of the foundation crosses reared both at 31{\pm}1$^{\circ}C$ and at $25{\pm}1^{\circ}C$ temperatures, are discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.4
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• pp.53-59
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• 2022

In this study, an enhanced first-order shear deformation theory is proposed to efficiently and accurately predict the thermo-mechanical-viscoelastic coupled behavior of laminated composite structures. To this end, transverse shearstress and displacement fields are independently assumed, and the strain-energy relationship between these fields issystematically established using the mixed variational theorem (MVT). In MVT, the transverse shear stress fields are obtained from the third-order zigzag model, whereas the displacement fields of the conventional first-order model are considered to amplify the benefits of numerical efficiency. Additionally, a transverse displacement field with a smooth parabolic distribution is introduced to accurately predict the thermal behavior of composite structures. Furthermore, the concept of Laplace transformation is newly employed to simplify the viscoelastic problem, similar to the linear-elastic problem. To demonstrate the performance of the proposed theory, the numerical results obtained herein were compared with those available in the literature.