• Tribology and Lubricants
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• 제17권4호
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• pp.297-306
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• 2001

Under the condition of variable density and specific heat, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined within some degree of Journal misalignment. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the condition of variable density and specific heat play important roles in determining friction and load of Journal bearing at high speed operation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.305-310
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• 2001

Within some degree of journal misalignment, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined under the condition of variable density and specific heat. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the effects of variable density and specific heat on shaft misalignment are significant in determining the load capacity of a journal bearing operating at high speed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.287-292
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• 2001

Under the condition of variable density and specific heat, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the condition of variable density and specific heat play important roles in determining friction and load of journal bearing at high speed operation.

• 대한기계학회논문집B
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• 제29권7호
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• pp.814-819
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• 2005

The phase change heat transfer has been applied to the processes of machines as well as of manufacturing. The cycle in a heat exchanger includes the phase change phenomena of coolant for air conditioning, the solidification in casting process makes use of the characteristics of phase change of metal, and the welding also proceeds with melting and solidification. To predict the phase change processes, the experimental and numerical approaches are available. In the case of numerical analysis, the Enthalpy method is most widely applied to the phase change problem, comparing to the other numerical methods, i.e. the Equivalent Specific Heat method and the Temperature Recovery method. It's because that the Enthalpy method is accurate and straightforward. The Enthalpy method does not include any correction step while the correction of final temperature field is inevitable in the Equivalent Specific Heat method and the Temperature Recovery method. When the temperature field is to be used in the calculation, however, there must be converting process from enthalpy to temperature in the calculation scheme of Enthalpy method. In this study, an improved method for the Equivalent Specific Heat method is introduced whose method dose not include the correction steps and takes temperature as an independent variable so that the converting between enthalpy and temperature does not need any more. The improved method is applied to the solidification process of pure metal to see the differences of conventional and improved methods.

• 한국안전학회지
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• 제16권4호
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• pp.160-167
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• 2001

Cracking in connote structures is one of the main issues of structural design next to ensuring the load-bearing capacity. Thermal analysis is used to prevent thermal mucking, but concrete properties are uncertain variable, and analysis results have uncertainty, too. In this study, sensitivity analysis is performed to investigate the effect of conductivity, specific heal and pouring temperature. The results show that lower conductivity and higher specific heat increase the maximum temperature and maximum tensile stress. The structure with internal restraint is mostly influenced by the change of conductivity and specific heat.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2008년도 추계학술대회
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• pp.153-160
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• 2008

This paper presents the log likelihood function for integrated models for ALT such as exponential-general Eyring, Weibull-temperature and specific heat, lognormal-temperature and specific heat. Additionally this paper estimates the system reliability and mean time to failure(MTTF) for series, parallel, k of n, and standby system using ALT linkage parameter. Lastly this study designs three variable reliability acceptance sampling(RAS) plans such as type I, II censored test, sequential test by the use of integrated models for ALT.

• 한국기계가공학회지
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• 제5권2호
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• pp.56-64
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• 2006

Rapid progress in many branches of technology has led to a demand on new materials such as high strength light weight alloys, powdered alloys and composite materials. The hydrostatic extrusion is essentially a method of extruding a clad rod through a die. In order to investigate the effect of the process conditions such as friction heat, deformation and clad thickness on the clad extrusion process, viscoplastic finite element simulations were conducted. A specific model for theoretical analysis used in this study is The single scalar variable version of Hart's model. An experiment also has been carried out using 1.5MN hydrostatic extruder with variable speed ram, LVDT and load cell for comparison. It is found that the hydrostatic extrusion pressure considering the effect of heat dissipation in this theoretical work was closer to the experimental pressure than the isothermal hydrostatic extrusion pressure.

• Tribology and Lubricants
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• 제23권1호
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• pp.1-8
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• 2007

Turbocharger bearings are under the circumstance of high temperature, moreover rotated at high speed. It is necessary to be designed to overcome the high temperature. So the type of oil inlet port, the inlet oil temperature and the sort of engine oil should be designed, controlled and selected carefully in order to reduce the bearing inside temperature. Therefore, in this study, the effects of the type of inlet oil port, inlet temperature and the sort of engine oil on the performance of a turbocharger bearing are to be investigated. It is found that the type of oil inlet ports, the control of inlet oil temperature and the selection of engine oil type play important roles in determining the temperature and pressure, then the friction and load of a turbocharger journal bearing at high speed operation.

• Journal of Welding and Joining
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• 제11권3호
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• pp.34-47
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• 1993

용접에서 발생하는 열응력 및 잔류응력을 해석하기 위한 유한요소용 모델을 개발하였다. 여러 가 지 변수의 연구를 통하여 Ramp heat input function과 Lumped모델을 제시하였다. 용접부에 열입 력을 점차적으로 주기 위하여 Ramp heat input을 이용하였으며 Ramp input을 통하여 이차원 모 델에서의 이동열원의 영향을 고려하였고 실험치와 비교에서 최적 ramp시간을 결정하였다. 다층용 접에서는 용접 pass 에 비례하여 계산시간이 증가한다. 따라서 후판용접의 잔류응력계산에는 막 대한 계산시간이 필요하며 이를 줄이기 위하여 Lumped 모델을 개발하였다. 이 Lumped모델에서 는 각 용접층에 들어있는 용접 pass들을 하나의 lumped pass으로 이용하였으며 각 pass를 따로 계산한 모델 및 시험치와의 비교를 통하여 최적 lumped technique을 제시하였다. *****Finite element models were developed for thermal and residual stress analysis for the specific welding problems. They were used to evaluate the effectiveness of the various welding heat input models, such as ramp heat input function and lumped pass models. Through the parametric studies, thermal-mechanical modeling sensitivity to the ramp function and lumping techniques was determined by comparing the predicted results with experimental data. The kinetics for residual stress formation during welding can be developed by iteration of various proposed mechanisms in the parametric study. A ramp heat input function was developed to gradually apply the heat flux with variable amplitude to the model. This model was used to avoid numerical convergence problems due to an instantaneous increase in temperature near the fusion zone. Additionally, it enables the model to include the effect of a moving arc in a two-dimensional plane. The ramp function takes into account the variation in the out of plane energy flow in a 2-D model as the arc approaches, travels across, and departs from each plane under investigation. A lumped pass model was developed to reduce the computation cost in the analysis of multipass welds. Several weld passes were assumed as one lumped pass in this model. Recommendations were provided about ramp lumping techniques and the optimum number of weld passes that can be combined into a single thermal input.

• 대한기계학회논문집B
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• 제22권12호
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• pp.1657-1668
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• 1998

In the analysis of a mushy solidification system with natural convection using a fixed grid method, the enthalpy method has been used to account for the release of latent heat. The variable viscosity, Darcy source, and hybrid methods have been employed for the velocity suppression in a mushy region. The choice of the values of solid viscosity and permeability constant in conjunction with the Darcy source term plays an important role in forming the location and shape of the phase boundaries. In this work the effects of these major parameters related to steady-state behavior in the system of mushy solidification are investigated through a simple test problem. The effective specific heat based on the spatial gradients of the enthalpy and temperature is adopted for the treatment of the release of latent heat. The effects of the Prandtl and Rayleigh numbers on the shape of mushy region are examined using the hybrid method.