• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.220-223
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• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔK$_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - ΔK in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.e.greatly affect a material with decreasing temperature.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.326-331
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• 2001

In this study. CT specimens were prepared from ASME SA5l6 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ in the range of stress ratio of 0.1 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔKsub/th/ in the early stage of fatigue crack growth ( Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da.dN -ΔK in RegionII, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• Journal of the Korean Wood Science and Technology
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• 제32권4호
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• pp.1-7
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• 2004

소나무 간벌재로 톱밥보드를 만든 후 우드세라믹을 제조하여 수지함침율 및 소성온도에 따른 우드세라믹의 표면온도의 변화를 조사하였다. 실리콘러버 히터의 표면온도가 증가함에 따라 우드세라믹의 표면온도도 빠른 속도로 증가하였으며, 히터의 설정표면온도가 70℃ 일때 수지함침율 80% 시편의 표면온도는 53.9 ℃이었으며, 소성온도 1,000℃ 조건으로 제조된 우드세라믹의 표면 온도는 54.2 ℃로 가장 높았다. 히터의 표면온도보다 우드세라믹 표면온도의 하강 속도가 느려 우드세라믹이 오랜 시간 열을 유지하고 있음을 알 수 있었다.

• 대한기계학회논문집B
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• 제21권12호
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• pp.1710-1719
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• 1997

An approximate analytical solution for the initial transient process of close-contact melting occurring between a phase change material kept at its melting temperature and an isothermally heated flat surface is derived. The model is so developed that it can cover both rectangular and circular cross-sectional solid blocks. Normalization of simplified model equations in reference to the steady solution enables the solution to be expressed in a generalized form depending on the liquid-to-solid density ratio only. A selected result shows an excellent agreement with the previously reported numerical data, which justifies the present approach. The solution appears to be capable of describing all the fundamental characteristics of the transient process. In particular, dependence of the solid descending velocity oft the density ratio at the early stage of melting is successfully resolved. The effects of other parameters except the density ratio on the transient behaviors are efficiently represented via the steady solution implied in the normalized result. A simple approximate method for estimating the effect of convection on heat transfer across the liquid film is also proposed.

• 대기
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• 제30권3호
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• pp.311-318
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• 2020

Impacts on the atmospheric circulation and ocean system over the Mediterranean during boreal summer are investigated using Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations (from 1911 to 2005). As the climate warms, global and remote effects lead to a strengthening in descending motion, an increase in sea surface temperature (SST) and surface dryness, but a decrease in marine primary production over the Western Mediterranean. The global effect is estimated from interannual variability over the global mean SST and the remote effect is driven by diabatic forcing generated from the South and East Asian summer monsoons. On the other hand, a local contribution leads to the strengthened descending motion and increased surface dryness over the Eastern Mediterranean, whereas the marine primary production over this region tends to increase due to possibly the urban wastewater and sewage. Our result suggests that particular attention needs to be paid to conserve the marine ecosystem over the Mediterranean.

• 대한원격탐사학회지
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• 제39권5_1호
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• pp.609-620
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• 2023

본 연구에서는 Sentienl-1 C-band synthetic aperture radar (SAR) 자료를 활용해 토양의 동결-융해 상태 구분을 위한 지표상태인자(surface state factor, SSF)를 산정하고, 기온, 초상온도, 지중온도 관측 자료와 비교를 통해 SSF 구분의 정확도를 분석하였다. 분석을 위한 SAR 자료는 우리나라 중부지방에 대해 2017년부터 2020년까지 4년 동안 관측된 Sentinel-1B descending node 116장을 구축하였으며, 동 기간의 농촌진흥청 토양수분 관측 지점 23곳에 대한 시 단위 기온, 초상온도, 10 cm 지중온도 자료를 구축하고 Sentienl-1B 영상의 촬영시각과 인접한 06:00 am 자료를 활용해 분석하였다. 전체 관측소에 대한 평균 정확도와 F1-score는 기온이 각각 0.63, 0.47, 초상온도가 0.63, 0.48, 지중온도가 0.57, 0.21로 나타났다. 겨울철(12~2월) 자료에 대한 평균 정확도와 F1-score는 기온이 각각 0.66, 0.76, 초상온도가 0.67, 0.76, 지중온도가 0.47, 0.44로 나타났다. 겨울철 자료의 정확도 상승은그외 시기에서 발생하는 오류가 포함되지 않기 때문인 것으로 보인다.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권1호
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• pp.73-83
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• 2000

The purpose of this study is to analyze and characterize the correlation of the thermal comfort sensation with physiological responses for men in winter indoor environment. A number of experiments were conducted under twenty different environmental conditions with college male students. Clinical information on each participant was reported in terms of electrocardiogram (ECG), electroencephalogram (EEG) and self-centered evaluation. The comfort zone in winter is found, throughout the study, at Standard New Effective Temperature (SET$T^+$) of 25.2$^{\circ}C$, Predicted Mean Vote (PMV) between 0.27 and 0.62, and Thermal Sensation Vote (TSV) in the range of -0.76 and 0.36. The largest difference in skin temperature is measured at the calf area with respect to air temperature changes. Skin sensitivity to environment temperature is explained as calf, head, chest and abdomen in descending order. Change in heat rate is analyzed to be in parallel with that of SET$T^+$.

• 한국생산제조학회지
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• 제22권3호
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• pp.380-387
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• 2013

In this study, two finite element (FE) models were developed to evaluate the thermal characteristics of a feeding axis of a CNC lathe. One was used for analysis of heat transfer to identify the temperature distribution of the feeding axis and then, the other was used for analysis of thermal deformation to evaluate its structural behavior based on the temperature distribution. The FE models were based on the test standard for the axial thermal displacement. The feeding velocity was composed of three steps: the ascending, constant, and descending velocities. Therefore, the heat generation and convection coefficient were calculated for each velocity and applied to the thermal FE model. The convection coefficient for the ball screw rotation was based on an experimental equation. The result of the analytical thermal displacement was compared with that of the experimental displacement to verify the finite element models.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.316-319
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• 2004

Resins using recycled PET offer the possibility of a lower source cost of materials for making useful polymer concrete products. The purposed of this paper is to propose the model for the stress-strain relation of recycled-PET polymer concrete at monotonic uniaxial compression and is to investigate for the stress-strain behavior characteristics of recycled-PET polymer concrete with different variables(strength, resin contents, curing conditions, addition of silane and ages). The maximum stress and strain of recycled-PET polymer concrete was found to increase with an increase in resin content, however, it decreased beyond a particular level of resin content. A ascending and descending branch of stress-strain curve represented more sharply at high temperature curing more than normal temperature curing. In addition, results show that the proposed model accurately predicts the stress-strain relation of recycled-PET polymer concrete.

• 환경영향평가
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• 제21권1호
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• pp.133-142
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• 2012

Convection Current Circulation System(CCCS) in stratified reservoir controls development of anaerobic condition and algal bloom during summer. In order to increase the CCCS effectiveness, we analyze diverse design parameters to make optimize the flow pattern in reservoir. In this study, we interpret the internal flow with installation and operation condition of CCCS based on CFD in reservoir. Design variables of CCCS is reservoir depth, stratification strength, distance of between CCCS and so on. Since reservoir depth and stratification strength in variables is depending on natural phenomenon, we evaluated current circulation effect by distance of CCCS and proposed the optimal design condition using CFD simulation. Flow and diffusion changes in water body was assessed by temperature and dye test. Changes in water floor temperature at 40m intervals was slowly descending over 37 hours. Dye diffusion simulation at 60m intervals, the radius of the spread between two devices were overlapped after 12 hours.