• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.2
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• pp.1-8
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• 2024

The expansion joint is installed to offset the expansion of the superstructure and must ensure sufficient gap during its service life. In detailed guideline of safety inspection and precise safety diagnosis for bridge, damage due to lack or excessive gap is specified, but there are insufficient standards for determining the abnormal behavior of superstructures. In this study, a data-based maintenance was proposed by continuously monitoring the expansion-gap data of the same expansion joint. A total of 2,756 data were collected from 689 expansion joint, taking into account the effects of season. We have developed a method to evaluate changes in the expansion joint-gap that can analyze the thermal movement through four or more data at the same location, and classified the factors that affect the superstructure behavior and analyze the influence of each factor through deep learning and explainable artificial intelligence(AI). Abnormal behavior of the superstructure was classified into narrowing and functional failure through the expansion joint-gap evaluation graph. The influence factor analysis using deep learning and explainable AI is considered to be reliable because the results can be explained by the existing expansion gap calculation formula and bridge design.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.701-706
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• 1999

The effect of siloxane oligomer content on thermal stability and internal stress of DGEBA epoxy resin was investigated. Siloxane-epoxy polymers having terminal epoxy group were prepared by reaction of siloxane-DDM prepolymer with DGEBA epoxy resin. Thermal stability was studied in terms of the initial decomposition temperature(IDT), temperature of maximum rate of weight loss($T_{max}$), integral procedural decomposition temperature(IPDT), and decomposition activation energy($E_t$) using TGA data. The thermal stability increased with increasing the siloxane oligomer content and showed a maximum value in the case of 5 wt% siloxane oligomer content in the blend system. While, the coefficient of thermal expansion(${\alpha}_r$) and the flexural modulus($E_r$) allowed us to study internal stress of the blend system. As the content of siloxane oligomer increases, the internal stress systematically decreases as decreasing both ${\alpha}_r$ and $E_r$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.48.1-48.1
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• 2011

In this presentation, We monitored weather data, such as global irradiance, ambient temperature, temperature of PV module, relative humidity and windspeed for 2 years, for determining accelerated test condition. then, we determined the temperature limit of accelerated test through weather data and FEM analysis. Detailed procedures will be summarized in this work. After analysing outdoor stress such as thermal stress, we decided main failure modes and mechanisms of PV module, especially solder joint of ribbon wire. we carried out the measurement of material properties such as thermal expansion coefficient for planning of accelerated test. we designed accelerated test based on FEM analysis results. we carried out thermal cycling test with 1 cell mini module for 3 months. We monitored the change of electrical performance every 1 week such as Voc, Isc, Pmax, etc. and then, we analized the ribbon wire/electrode intefaces. Detailed results will be summarized in this work.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.10
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• pp.1046-1052
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• 2007

Elastic-plastic structural analysis for regenerative cooling chamber of gas generator was performed. Uniaxial tension test was conducted for STS316L at room and high temperature conditions to get the material data necessary for the structural analysis of the chamber which was operated under thermal load and high internal pressure. Physical properties including thermal conductivity, specific heat and thermal expansion were also measured. The structural analysis for four different types of regenerative cooling chamber of gas generator revealed that increased cooling performance decreased the thermal load and strain of the cooling channel structure. The results propose that in order for the regenerative cooling gas generator chamber to have high structural stability with endurance to high mechanical and thermal loads, it is important for the chamber to be designed to have high cooling performance.

• Journal of the Korean Chemical Society
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• v.40 no.1
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• pp.81-86
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• 1996

The physical properties of epoxy molding compound (EMC) according to the change of softening point of epoxy resin have been investigated in order to study the relationship between the properties of o-cresol novolac epoxy resin, which is main component of EMC for semiconductor encapsulation, and EMC. The softening points of used epoxy resin are 65.1 $^{\circ}C$, 72.2 $^{\circ}C$, and 83.0 $^{\circ}C$, respectively. The flexural strength and flexural modulus as mechanical properties were measured, and thermal expansion coefficient, thermal conductivity and glass transition temperature (Tg) as thermal properties, and spiral flow as moldability have been investigated to see the change of physical properties of EMC. The flexural modulus, thermal expansion coefficients in the glass state (${\alpha}_1$), and thermal conductivity of EMC were found to be keep constant value irrespective of the change of softening point, but Tg increased with softening point of epoxy resin, and the spiral flow decreased with that. It can be considered that these phenomena are due to the increase of crosslinking density of EMC according to the increase of softening point. The transition points were found out in the thermal expansion coefficient data in the rubbery state (${\alpha}_2$) and the flexural strength data. These can show the decrease of filler dispersion according to increase of epoxy resin viscosity.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1280-1286
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• 2023

MgF₂ as a moderator material has been extensively used in the beam shaping assembly (BSA) that plays an important role in the boron neutron capture therapy (BNCT). Regarded as important for applications, the thermal neutron scattering data of MgF₂ were calculated, based on the phonon expansion model. The structural properties of MgF₂ were researched by the VASP code based on the ab-initio methods. The PHONOPY code was employed to calculate the phonon density of states. Furthermore, the NJOY code was used to calculate the thermal neutron scattering data of MgF₂. The calculated inelastic cross sections plus absorption cross sections are in agreement with the available experimental data. The neutron transport in the BSA has been simulated by using a hybrid Monte-Carlo-Deterministic code NECP-MCX. The results indicated that compared with the calculation of the free gas model, the thermal neutron flux and epithermal neutron flux at the BSA exit port calculated by using the thermal neutron scattering data of MgF₂ were reduced by 27.7% and 8.2%, respectively.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.291-296
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• 2000

Usually the contact between fin collar and tube surface for fin-tube heat exchanger is secured by mechanical expansion of the tubes. The objective of the present study is to develop a method of measuring the thermal contact resistance between fin collar and tube surface for fin-tube heat exchanger. Also an experimental work has been performed to evaluate the thermal contact resistance, and a rigorous numerical analysis has been employed to calculate the contact resistance from the measured data. The experiments have been conducted fur the fin-tube heat exchangers with the tube of outer diameters 7 and 9.52 mm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.779-789
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• 2015

Because cable-supported bridges have long spans and large members, their movements and geometrical changes by temperatures tend to be bigger than those of small or medium-sized bridges. Therefore, it is important for maintenance engineers to monitor and assess the effect of temperature on the cable-supported bridges. To evaluate how much the superstructure expands or contracts when subjected to changes in temperature is the first step for the maintenance. Thermal movements of a cable-stayed bridge in service are evaluated by using long-term temperatures and displacements data. Displacements data are obtained from extensometers and newly installed GNSS (Global Navigation Satellite System) receivers on the bridge. Based on the statistical data such as air temperatures, each sensor's temperatures, average temperatures and effective temperatures, correlation analysis between temperatures and displacements has been performed. Average temperatures or effective temperatures are most suitable for the evaluation of thermal movements. From linear regression analysis between effective temperatures and displacements, the variation rate's of displacement to temperature have been calculated. From additional regression analysis between expansion length's and variation rate's of displacement to temperature, the thermal expansion coefficient and neutral point have been estimated. Comparing these parameters with theoretical and analytical results, a practical procedure for evaluating the real thermal behaviors of the cable-supported bridges is proposed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.257-262
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• 1997

A compact measurement system is developed to measure in-process errors due to thermal deformation of a machine tool, this system is composed of a gauge, 5gap-sensors and a PC. The gauge is made of invar, which is a material that has a very low thermal expansion coefficient. A new neural network model is constructed to estimate thermally induced machine tool errors based on the measured data,the given data,that is a width of cut,a depth of cut, a feed rate, a spindel speed etc, and the calculated data. The detail of the model proposed is described in the paper together with the experimental methodologies using a proposed compact measurement system to examine the validity of the proposed approach.

• Korean Journal of Remote Sensing
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• v.37 no.4
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• pp.665-685
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• 2021

This study focused on the a 20-year evaluation of the dynamism of critical thermal anomalies in Busan metropolitan area prompted by unusual infrastructural development and demographic growth rate. Archived Landsat thermal data derived-LST was the major input for UTFVI and hot spot analysis (Getis-Ord Gi^*). Results revealed that the surface urban heat island-affected area has gradually expanded overtime from 23.32% to 32.36%; while the critical positive thermal anomalies (level-3 hotspots) have also spatially increased from 19.88% in 2000 to 23.56% in 2020, recording a net LST difference of > 5℃ between the maximum level-3 hotspot and minimum level-3 coldspot each year. It is been observed that thermal conditions of Busan have gradually deteriorated with time, which is potentially inherent in the rate of urban expansion. Thus, this work serves as an eye-opener to powers that be, to think and act constructively towards a sustainable thermal conform for city dwellers.