• Journal of Welding and Joining
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• 제34권2호
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• pp.16-21
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• 2016

Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW), especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficient toughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thickness were compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the inside of the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.

• 한국해양공학회지
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• 제16권2호
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• pp.72-79
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• 2002

In this study, time-dependent distributions of temperature and stresses, in the box-column welded from ultra thick plates with center segregation, has been analyzed by the commercial finite element package SYSWELD+, for several types and angles of groove. The major points of investigation are the optimum type and angle of groove that minimize weld stress specially at the center segregation, as well as temperature distribution, residual stresses and changes in the mechanical properties. The results can be summarized as follows; 1) Generally the thermal cycle at the root of groove exhibits relatively rapid cooling pattern, however, most of the other part weldment have a slow cooling pattern in all groove types. 2) Most of the micro-structures of weldment are composed of ferrite and pearlite, meanwhile we could find martensite and bainite locally a the root of the groove. 3) Optimum groove type for high heat input welding of box-column corner is a double groove type, and the optimum angle for the groove is 30~$45^{\circ}$ that minimize deformation and weld stress at the center segregation.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1054-1064
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• 2002

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.

• Journal of Welding and Joining
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• 제13권3호
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• pp.116-124
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• 1995

This paper presents an analytical solution to predict the transient temperature distribution in fillet arc welding including the effect of molten metal. The solution is obtained by solving a transient three-dimensional heat conduction equation with convection boundary conditions on the surfaces of a plate, and mapping the infinite plate onto the fillet weld geometry with energy equation. The electric heat input on the fillet weld and on the infinite plate is assumed to have a combination of two bivariate Gaussian distribution. To check the validity of the solution. FCA welding experiments were performed under various welding conditions. The actual isotherms of the weldment cross-sections at various distances from the arc start point are compared with those of simulation result.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 춘계학술대회 논문집
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• pp.111-116
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• 1999

Over the last few years, there has been a growing interest in quantitative representation of heat transfer and fluid flow phenomena in weld pools in order to relate the processing conditions to the quality of the weldment produced and to use this information for the optimization and robotization of the welding process. Normally, a theoretical model offers a powerful alternative to estimate the important input parameters and to calculate the effects of varying any of parameters. To solve this problem, a transient 2D(two-dimensional) heat conduction and a transient 2D axisymmetric heat and fluid model were developed for determining weld bead geometry and temperature distribution for the GMA(Gas Metal Arc) welding process. The equation was solved using a general thermofluid-mechanics computer program, PHOENICS code, which is based on the SIMPLE algorithm. The simulation results showed that the calculated bead geometry from two developed models reasonably agree with the experiment result.

• Journal of Welding and Joining
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• 제13권1호
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• pp.138-144
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• 1995

Recently, as the industrial structure tends to become large, the thickness of structural plate becomes thicker. Therefore, the thicker the plate of welded structure is, the larger the shape of welded joint. The effect of large heat input makes large heat affected zone(HAZ). These bring to complict welding residual stress and to weaken material, which may cause extremely harm to the safety of structures. Nevertheless, welding is design is regulated by the KS, JIS or standard in the resister of shipping such as KR, ABS or LR. However, these rules are based on rather experimental than theoretical. In this study, the computer program of heat conduction, considering un-steady state and quasi-steady state, is developed for optimizing(minimizing) a shape of welded joint. The characteristics of heat on the welded joints with various shapes are clarified by the results of the analyses.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2020년도 학술발표회
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• pp.366-366
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• 2020

The drought is one of the extreme natural disasters observed in any climate zone and it is due to the deficiency in moisture. The flash drought is identified recently as a subdivision of drought and it is an extreme event distinguished by sudden onset and rapid intensification of drought conditions with severe impacts. The main cause for the flash drought is coupled situation due to precipitation deficit and high evapotranspiration. Hence, heat waves plays major role in identification of flash drought. Therefore, this study focused on identifying changes in distribution of heat waves for Korean Peninsula. The daily maximum and minimum temperature data were used in this study. The heat wave, heat wave intensity and heat wave intensity index were derived. The results of the study would be an input for the future studies on identification of flash drought in Korean Peninsula.

• 설비공학논문집
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• 제18권1호
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• pp.24-30
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• 2006

Three liquid cooling heat exchangers for cooling of telecommunication equipment were designed and their cooling performances were tested. The liquid cooling heat exchangers had twelve rectangular channels $(5\times3 mm)$ with different flow paths of 1, 4, and 12. Silicon rubber heaters were used to provide heat flux to the test section. Heat input was varied from 75 to 400 W, while flow rate and inlet temperature of working fluid were altered from 1.2 to 4.0 liter/fin and from 15 to 3$30^{\circ}C$, respectively. The 4-path heat exchanger showed lower and more uniform average inner temperatures between heaters and the surface of heat exchanger than those of the others. To obtain optimal distribution of working fluid to each channels of liquid cooling heat exchangers, 2-3-2 and 4-3 type tube distributors were designed, and their distribution performances of working fluid were numerically and experimentally investigated. The distributor of the 2-3-2 type showed superior distribution performance compared with those of the 4-3 type distributor.

• 한국강구조학회 논문집
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• 제10권4호통권37호
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• pp.709-720
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• 1998

용접잔류응력의 모재두께방향을 포함하는 3차원 분포를 파악하기 위해, 용접상세를 변화시킨 필렛용접이음을 대상으로 해서 실험 및 해석을 수행하였다. 특히, 지금까지 계측이 곤란했던 필렛용접이음의 용접루트부의 잔류응력을 실측하였다. 파라메타로써는 용접입열량과 용접층수를 취급하고, 모재두께방향을 포함하는 3차원 잔류응력의 분포를 조사하였다. 그 결과, 입열량이 증가하면, 용접토우와 루트부를 포함하는 용접부에서는 잔류응력의 크기에 변화가 거의 없지만, 인장잔류응력의 영역이 크게 나타났다. 또 단층과 다층용접의 비교에서는, 다층용접 쪽이 단층용접보다 잔류응력이 상당히 낮음을 알 수 있었다. 용접부 근방의 인장잔류응력의 영역도 다층용접 쪽이 단층용접보다 작게 나타난 것을 알 수 있었다.

• Tribology and Lubricants
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• 제13권4호
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• pp.26-32
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• 1997

The heat generation of the angular contact and the deep groove ball bearing is studied experimentally and numerically. The temperature variation of the inner and outer races and the temperature increase distribution are measured for the shaft rotational speeds, preloads, viscosities of the lubricant and lubrication methods. The measured temperature distributions are used as the input data of the numerical simulation to estimate the heat generation rate at the bearing. The temperatures of the inner and outer race increase more rapidly and approach faster to their steady values as the rotational speed increases. The optimal viscosity of the oil to minimize the heat generation is 8~10 cSt at 4$0^{\circ}C$ when the oil-air lubrication method is adopted. The heat generation of the bearing increases with the rotational speed and depends more on the lubrication method than on the preload variation.