• Structural Engineering and Mechanics
• /
• v.69 no.1
• /
• pp.33-42
• /
• 2019

Thermal cracks are cracks that commonly form at early ages in mass concrete. During the concrete pouring process, the elastic modulus changes continuously. This requires the time domain to be divided into several steps in order to solve for the temperature, stress, and displacement of the concrete. Numerical simulations of thermal crack propagation in concrete are more difficult at early ages. To solve this problem, this study divides crack propagation in concrete at early ages into two cases: the case in which cracks do not propagate but the elastic modulus of the concrete changes and the case in which cracks propagate at a certain time. This paper provides computational models for these two cases by integrating the characteristics of the extended finite element algorithm, compiles the corresponding computational programs, and verifies the accuracy of the proposed model using numerical comparisons. The model presented in this paper has the advantages of high computational accuracy and stable results in resolving thermal cracking and its propagation in concrete at early ages.

• Journal of the Korean housing association
• /
• v.12 no.2
• /
• pp.191-198
• /
• 2001

The aim of this research was to examine the thermal performance of the flat roof in proportion to various directional changes, the results of which were drawn from the miniature model experiment. In this process, various thermal environmental factors were measured and compared with one another to research their aspects of changes. The brief results of this research are as follows: 1) The indoor temperature and load per hour in proportion to directional changes shows the same degree of changes. As for the results of the clear-sky and cloudy-sky experiments, both of them generally appear advantageous in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite slight differences in the indoor temperature and load per hour in proportion to directional changes. 2) As for the total load of degree day per direction of the clear-sky and cloudy-sky experiments, both of them shows their advantageous results in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite minor differences in their loads. 3) As for the peak load of degree hour, while the clear-sky experiment shows its advantage in the order of $S-30^{\cire}C$-E, S, $-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, the cloudy-sky experiment does so in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, E, $S-60^{\cire}C$-W, $S-60^{\cire}C$-E.

• Journal of Biosystems Engineering
• /
• v.25 no.4
• /
• pp.293-300
• /
• 2000

Automated greenhouse production system often require crop growth monitoring involving accurate quantification of plant physiological properties. Conventional methods are usually burdensome, inaccurate, and harmful to crops. A thermal image analysis system can accomplish rapid and accurate measurements of physiological-property changes of stressed crops. In this research a thermal imaging system was used to measure the leaf-temperature changes of several crops according to nutrient stresses. Thermal images were obtained from lettuce, cucumber, and pepper plants. Plants were placed in growth chamber to provide relatively constant growth environment. Results showed that there were significant differences in the temperature of stressed plants and non-stressed plants. In a case of the both N deficiency and excess, the leaf temperatures of cucumber were $2^{\circ}C$ lower than controlled temperature. The leaf temperature of cucumber was $2^{\circ}C$ lower than controlled temperature only when it was under N excess stress. For the potassium deficiency or excess stress, the leaf temperaures of cucumber and hot pepper were $2^{\circ}C$ lower than controls, respectively. The phosphorous deficiency stress dropped the leaf temperatures of cucumber and hot pepper $2^{\circ}C$ and $1.5^{\circ}C$ below than controls. However, the leaf temperature of lettuce did not change. It was possible to detect the changes in leaf temperature by infrared thermography when subjected to nutrition stress. Since the changes in leaf temperatures were different each other for plants and kinds of stresses, however, it is necessary to add a nutrient measurement system to a plant-growth monitoring system using thermography.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.04a
• /
• pp.43-48
• /
• 2000

Composite materials have been increasingly used in automotive and aircraft industries, naturally leading to active researches on the materials. The carbon-epoxy composite is selected to study its thermal characteristics. During multiple thermal cycles composed of repeated cooling and heating variations of elastic constants are investigated to understand thermal effects on the carbon-epoxy composite. In this investigation longitudinal resonance method and flexural resonance method was used to characterize. The values of $E_1$ show small amount of increases depending on number of cycles of the thermal fatigue processes whereas values of $G_13$ do not indicate noticeable changes. Also, in cases of $E_2$ and $G_23$ their values decrease to a certain extend in initial stages after applications of thermal fatigue processes. However, the number of cycles of the applied thermal fatigue processes does not seem to affect their values.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.04a
• /
• pp.91-95
• /
• 2005

A heat dissipation modeling method of EEE parts is developed for thermal design and analysis of an satellite electronic equipment. The power consumption measurement value of each functional breadboard is used for the heat dissipation modeling method. For the purpose of conduction heat transfer modeling of EEE parts, surface heat model using very thin ignorable thermal plates is developed instead of conventional lumped capacity nodes. The thermal plates are projected to the printed circuit board and can be modeled and modified easily by numerically preprocessing programs according to design changes. These modeling methods are applied to the thermal design and analysis of CTU and verified by thermal cycling and vacuum tests.

• Journal of Sensor Science and Technology
• /
• v.18 no.2
• /
• pp.103-109
• /
• 2009

Thermal time constant measurement system was designed and fabricated to measure the thermal time constant, which shows a dynamic property of the thermocouple. Type K thermocouple samples were fabricated with variable shape each other and the thermal time constants of thermocouples were measured using the home-made thermal time constant measurement system. Thermal time constants of 12 type K thermocouple samples were distributed from 0.03 s to 8.2 s. It showed experimentally that the thermal time constant of thermocouple was increased linearly for the increase of the sheath diameter of thermocouple.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.5
• /
• pp.459-465
• /
• 2013

In the manufacturing process of steel plates, materials at high temperatures above $800^{\circ}C$ are rapidly cooled by using a circular impinging water jet to determine their strength and toughness. In this study, the basic heat and fluid flow is solved by using the existing numerical model for boiling heat transfer. Actually, steel undergoes a phase change from austenite to ferrite or bainite during the cooling process. The phase change induces changes in its thermal properties. Instead of directly solving the phase change and the material cooling together, we solve the heat transfer only by applying the thermal properties that vary with temperature, which is already known from other studies. The effects of the changes in the thermal properties on the cooling of steel and the necessity of calculating the phase change are discussed.

• The Korean Journal of Food And Nutrition
• /
• v.27 no.1
• /
• pp.112-119
• /
• 2014

Ohmic heating uses electric resistance heat which occurs equally and rapidly inside food when the electrical current is transmitted into. Prior to the study, we have researched the potato starch's thermal property changes during ohmic heating. Comparing with conventional heating, the gelatinization temperature and the range of potato starch treated by ohmic heating are increased and narrowed respectively. Herein, we have studied thermal property changes of wheat, corn, potato and sweet potato starch by ohmic heating as well as conventional heating. And then we measure the water holding capacity of starches. Annealing of starch is a heat treatment method heated at 3~4% below the gelatinization point. This treatment changes the starch's thermal property. In the DSC analysis of this study, the $T_o$, $T_p$, $T_c$ of all starch levels have increased, and the $T_c$-$T_o$ narrowed. In the ohmic heating, the treatment sample is extensively changed but not with the conventional heating. From the ohmic treatment, increases from gelatinization temperature are potato ($8.3^{\circ}C$) > wheat ($5.3^{\circ}C$) > corn ($4.9^{\circ}C$) > sweet potato ($4.5^{\circ}C$), and gelatinization ranges are potato ($7.9^{\circ}C$), wheat ($7.5^{\circ}C$), corn ($6.1^{\circ}C$) and sweet potato ($6.8^{\circ}C$). In the case of conventional treatment, water holding capacity is not changed with increasing temperature but the ohmic heating is increased. Water holding capacity is related to the degree of gelatinization for starch. This result show that when treated with below gelatinization temperature, the starches are partly gelatined by ohmic treatment. When viewing the results of the above, ohmic treatment is enhanced by heating and generating electric currents to the starch structure.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.28 no.2
• /
• pp.137-143
• /
• 2008

The spherical glasses lenses are typically classified into two groups such as (+) diopter lens and (-) diopter lens by the refractive power index. The thermal deformation of a lens is occurred by external heat source and is changed respected to the diopter of a lens. In this paper, the thermal deformation of spherical glasses lenses were quantitatively measured by using ESPI (electronic speckle pattern interferometry) which has an advantage that the non-contact, non-destructive and precise deformation measurement is available due to the coherency characteristic. The temperature changes were measured by IR camera. It makes experiments over 14 types of the plastic glasses lenses. From the results, it was confirmed that the larger diopter lens showed the less thermal deformation in case of the (+) diopter lens. On the other hand, the thermal deformation of the (-) diopter lens was measured with uniform pattern when the same temperature changes were applied. Also, it was found that the thermnal deformation of the (+) diopter lens is less than that of the (-) diopter lens. Therefore, it is expected that when the thermal deformation is occurred to the various types of the lens, the variation of the focal length caused by the thermal distortion of a lens would be measured quantitatively.

• The Journal of the Acoustical Society of Korea
• /
• v.23 no.7
• /
• pp.503-513
• /
• 2004

In this paper, the thermal sensitivity, i .e. the temperature rise per unit acoustic power, was newly defined and proposed as a performance parameter of a tissue mimicking material. Eatable tofu (bean curd) manufactured by a factory was selected as a sample material for the experiment. The temperature changes were measured not only with the variation of ultrasonic irradiation time, acoustic power, depth from the sample surface. and the distance from the source transducer while adjusting the frequency to 8 MHz but also with the variation of frequency while acoustic power. depth from the sample surface. and the distance from the source transducer keeping constant. As a result of a consideration for the transformation of the measured temperature changes to thermal sensitivities. the thermal sensitivity was found to be sufficient to use as a Performance parameter for tissue mimicking material. The tofu as a tissue mimicking material showed the maximum thermal sensitivity at 10 MHz, as is a significant result to imply the possibility that the thermal sensitivity of real human tissue strong1y depends on the frequency.