• Asian Journal of Turfgrass Science
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• v.16 no.2
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• pp.107-114
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• 2002

In this study, We measured air temperature in a vegetated area to investigate if stand types and height affect air temperature. With the measured data, we analyzed the relation-ships between air temperature vs. ground cover type, vegetated area, stand structure, stand density, and tree volume by regression analysis. The results show that the paved area and open field have higher air temperatures than the vegetated area and water-related areas. Among the stand types, the stand with overstory and sub-overstory showed relatively low are temperature. The stand with overstory had lower air temperature than the stand with sub-overstory. Increasing stand density was effective for lowering air temperature.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.112-120
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• 2012

A numerical model considering the internal vaporization and the creep effect, in the form of a analytical program, for tracing the behavior of high strength concrete(HSC) members exposed to fire is presented. The two stages, i.e., spalling procedure and fire resistance time, associated with the thermal, moisture flow, creep and structural analysis, for the prediction of fire resistance behavior are explained. The use of the analytical program for tracing the response of HSC member from the initial pre-loading stage to collapse, due to fire, is demonstrated. Moisture evaporates, when concrete is exposed to fire, not only at concrete surface but also at inside the concrete to adjust the equilibrium and transfer properties of moisture. Finite element method is employed to facilitate the moisture diffusion analysis for any position of member, so that the prediction method of the moisture distribution inside the concrete members at fire is developed. The validity of the numerical model used in this program is established by comparing the predictions from this program with results from others fire resistance tests. The analytical program can be used to predict the fire resistance of HSC members for any value of the significant parameters, such as load, sectional dimensions, member length, and concrete strength.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.71-80
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• 2013

Fire-resistant (FR) test data for a square concrete-filled steel tube (CFT) columns consisting of high-strength steel (fy>650MPa) and high strength concrete (fck>100MPa) under axial loads are insufficient. The FR behavior of square high-strength CFT members was investigated experimentally for two specimens having ${\Box}-400{\times}400{\times}15{\times}3,000mm$ with two axial load cases (5,000kN and 2,500kN). The results show that the FR performance of the high-strength CFT was rapidly decreased at earlier time (much earlier at high axial load) than expected due to high strength concrete spalling and cracks. In addition, a fiber element analysis (FEA) model was proposed and used to simulate the fiber behaviour of the columns. For steel and concrete, the mechanical and thermal properties recommended in EN 1994-1-2 are adopted. Test results were compared to those of numerical analyses considering a combination of temperature and axial compression. The numerical model can reasonably predict the time-axial deformation relationship.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.95-105
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• 2014

Reinforced concrete (RC) shield tunnel lining must be designed for fireproof performance because the lining is sometimes exposed to very high temperature due to traffic accidents. Both experimental and numerical studies are carried out to evaluate fire resistance performance of precast RC tunnel lining systems. In the experimental studies, six full-scale precast RC tunnel segments are exposed to fire in order to examine the influence of various parameters on the fire resistance performance of precast RC tunnel lining. We used the temperature curve of the RABT criteria, which are severe conditions of fire temperatures. The fire test showed that the explosive spalling was not observed by substituting concrete to PP fiber reinforced concrete. A transient heat flow analysis was carried out in consideration of the material properties that change with temperature, and the results showed good agreement with the test results.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.17-26
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• 2024

Aircraft engines are exposed to high temperatures, high pressures, and stress caused by the rotation of the turbine shaft during flight. These loads can result in microcracks both on the inside and outside surfaces of the structure. Consequently, this can lead to structural defects and negatively impact the lifespan of the parts. To proactively prevent these defects, a finite element analysis is carried out to identify cracks. However, this process is time-consuming and requires significant effort due to the repetitive nature of crack modeling. This study aims to develop a crack modeling method based on the finite element model. To achieve this, the Constrained Delaunay Triangulation (CDT) technique is employed to triangulate the space while considering limitations on point connections. The effectiveness of this method is validated by comparing stress intensity factors for semi-elliptical cracks in plates and cylindrical vessels. This approach proves to be a valuable tool for crack analysis studies.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.617-626
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• 2021

During supersonic flight of vehicles, the thermal behavior of structures under high-temperature environment is important for thermal-structural design. In this study, full-field thermal deformation and stress concentration of the notched structure was performed using global-local multi-digital image correlation (multi-DIC) systems. This techniques were developed and implemented by multi-DIC systems consists of 2D DIC system and 3D DIC system. The specimen was heated in a heating chamber to achieve the thermal expansion behavior. Then the images of structure's deformation and stress concentration at various temperature were recorded and analyzed by multi-DIC system. Afterward, full-field thermal deformation of the notched structure was determined with DIC technique and stress concentration at the notched structure was calculated by further processing. Finite element analysis of the notched structure is performed in ABAQUS^TM and the results of the experiments show good agreement with those obtained from simulation. The results achieved in this study show the efficiency of the muilti-DIC method in thermal deformation as well as stress concentration of notched structure.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.121.2-121.2
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• 2010

제주도는 지질학적으로 제4기에 형성된 화산섬으로 지금까지 고온의 지열징후는 보고된 바 없으나, 남한에서 가장 최근까지 화산활동이 있었던 것으로 기록되어 있어 화산활동과 관련된 심부 지열자원 부존 가능성은 아직 열려있다고 할 수 있다. 본 연구에서는 제주도에서 지열부존 가능성을 타진하고 제주도 심부 지질구조 파악을 목적으로 2차원 및 3차원 자기지전류 (MT) 탐사를 수행하였다. 탐사는 중산간지역에서 한라산을 중심으로 동, 서, 남, 북의 4방향 4측선과 제주 서부지역에 남북방향의 1측선을의 총 5개 측선에 대해 수행하였으며, 이에 대한 MT 탐사자료의 2차원 및 3차원 역산을 통하여 한라산 하부 및 주변의 심부 지질구조를 파악하고자 하였다. 역산 해석 결과는 천부 구조는 기존 시추조사 결과 밝혀진 층서구조의 형태를 잘 나타내어 획득된 자료의 신뢰도가 높음을 지시하였다. 즉, 제주도 최 상부를 피복하고 있는 현무암 등의 화산암류는 고비저항(수백 ohm-m)으로, 그 하부의 해성 미고결퇴적층(U층 및 서귀포층)은 저비저항으로, 그리고 최하부의 응회암이나 화강암으로 구성된 기반암은 1,000 ohm-m 이상의 고비저항 층으로 잘 구분되어 나타났다. 특히, 제주도에서 특징적으로 해수면 하부 수십 ~ 수백 m에 존재하는 것으로 알려진 미고결퇴적층이 10 ohm-m 내외로 측선 전반에 걸쳐 나타났다. 이는 기존의 시추결과에서 미고결 퇴적층이 제주도 전역에 걸쳐 해수면 하부 100 m 내외의 심도에서 관찰되는 것과 일치하는 결과이다. 기반암 하부에서는 특징적으로 모든 측선의 중앙부에서 저비저항 이상대가 영상화되었으며 이는 2차원 역산과 3차원 역산해석에서 공통적으로 나타났다. 특히, 3차원 해석에서는 이러한 저비저항 이상대가 한라산 정상에서 서북쪽 부근에 나타나는데 이는 과거의 화산활동과 관련된 지질학적인 구조에 의한 영향일 가능성과 측선의 양단과 중앙에서 주변 바다의 영향이 다르게 나타나기 때문일 가능성으로 볼 수 있다. 즉, 전자는 심부에 발단된 각각의 파쇄대가 모든 측선의 중앙부에서 교차하거나 이를 통한 한라산의 생성과정과 연관된 지질학적인 구조일 가능성을 의미한다. 만약 한라산을 형성한 화성활동의 영향이 아직 지하 심부에 남아있다면 지열수의 부존 혹은 마그마의 통로가 되었을 단층의 영향으로 한라산 하부에 저비저항 이상대로 나타날 가능성이 높다. 그러나 후자에 의한 가능성도 배제할 수는 없으므로 향후 주변바다에 대한 영향을 고려한 3차원 역산해석이나 심부시추 등을 통한 상세한 지질조사 등 추가적인 연구가 이루어져야 할 것으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.10
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• pp.1025-1032
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• 2012

The flash lamp annealing (FLA) process has been considered highly promising for manufacturing low-temperature polysilicon on large-scale backplanes. Based on a theoretical estimation, this study clarifies the critical mechanisms of glass backplane deformation during the FLA process. A simulation using a commercial FEM code with viscoelastic models shows that the local region, whose temperature is larger than the glass softening point, undergoes permanent structural shrinkage owing to stress relaxation. For larger backplanes (4th Gen), structural shrinkages and gravitational deflection are critical to deformation in the FLA process, resulting in an "M" shape; in smaller backplanes (0th Gen), the latter is negligible, resulting in a "U" shape.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.4
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• pp.497-503
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• 2012

The aim of this study was to optimize S-tube shape of heat exchanger in term of reducing the size of tube bundle and improving the mechanical properties such as the thermal stress and resonance. The geometric parameters such as offset length, the straight distance between one end and other end of tube, the tube length in straight portion and fillet radius was assessed as a valid parameters. The structural analysis was performed to estimate the structural characteristics. Main effect analysis was performed to investigate the main effect for the various geometric parameters. The response surface methodology was employed to establish mathematical approximation models as a function of the geometric parameters of the S-tube. Also, The optimization was performed to optimize geometric parameters of S-tube using the regression equations and optimization tool. The optimized tube shape has been proposed. Those could be used in the heat exchanger design used in high temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.665-671
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• 2013

In a Korean Generation IV prototype sodium-cooled fast reactor (SFR), various types of high-temperature heat exchangers such as IHX (intermediate heat exchanger), DHX (decay heat exchanger), AHX (air heat exchanger), FHX (finned-tube sodium-to-air heat exchanger), and SG (steam generator) are to be designed and installed. In this study, the high-temperature design and integrity evaluation of the sodium-to-air heat exchanger AHX in the STELLA-1 (sodium integral effect test loop for safety simulation and assessment) test loop already installed at KAERI (Korea Atomic Energy Research Institute) and FHX in the SEFLA (sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger) test loop to be installed at KAERI have been performed. Evaluations of creep-fatigue damage based on full 3D finite element analyses were conducted for the two heat exchangers according to the high-temperature design codes, and the integrity of the high-temperature design of the two heat exchangers was confirmed.