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RISS 인기검색어
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- 저자 : 황철호(CheolHo Hwang) (검색결과 6 건)
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서준호(Junho Suh),황철호(Cheolho Hwang) 한국트라이볼로지학회 2016 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.32 No.1
This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.
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서준호(Junho Suh),황철호(Cheolho Hwang) 한국트라이볼로지학회 2021 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.37 No.1
This study shows the effect of the thermal boundary condition around the tilting pad journal bearing on the static and dynamic characteristics of the bearing through a high-precision numerical model. In many cases, it is very difficult to predict or measure the exact thermal boundary conditions around bearings at the operating site of a turbomachine, not even in a laboratory. The purpose of this study is not to predict the thermal boundary conditions around the bearing, but to find out how the performance of the bearing changes under different thermal boundary conditions. Lubricating oil, bearing pads and shafts were modeled in three dimensions using the finite element method, and the heat transfer between these three elements and the resulting thermal deformation were considered. The Generalized Reynolds equation and three-dimensional energy equation that can take into account the viscosity change in the direction of the film thickness are connected and analyzed by the relationship between viscosity and temperature. The numerical model was written in in-house code using MATLAB, and a parallel processing algorithm was used to improve the analysis speed. Constant temperature and convection temperature conditions are used as the thermal boundary conditions. Notably, the conditions around the bearing pad, rather than the temperature boundary conditions around the shaft, have a greater influence on the performance changes of the bearing.
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자기장 내 철가루 움직임의 실시간 시뮬레이션 및 시각화
윤원배(WonBae Yoon),이남일(Namil Lee),황철호(CheolHo Hwang),한정현(JungHyun Han) 한국HCI학회 2014 한국HCI학회 학술대회 Vol.2014 No.2
자기장 내의 철가루 입자들은 서로 자기력을 주고받으며 자기력선 모양을 따라 배치된다. 본 논문은 자기장 영향권에 있는 종이에 뿌려진 철가루의 움직임을 실시간으로 시뮬레이션하는 기법을 제안한다. 이 기법의 핵심 내용은 각 철가루에 미치는 주변 철가루의 힘을 계산하는 대신 가상의 자성체로부터 받는 힘을 계산하는 것이다. 가상의 자성체는 자석이 생성한 자기장과 철가루의 분포 두 가지를 고려하여 배치되고, 철가루들은 가까운 가상의 자성체들로부터 자기력을 받아 움직이게 된다. 제안된 기법을 사용한 결과는 실제 철가루 실험 결과와 매우 유사하여 초중등 과학교과목 가상 실험에 사용될 수 있을 것으로 판단된다. When we scatter iron filings in a magnetic field, iron filing particles form the shape of the magnetic field lines. In this paper, we propose an efficient real-time method that simulates the movement of iron filings in 2D space. The proposed method uses the force from a set of virtual magnets instead of the force from the particle pairs. The virtual magnet positions are determined by estimating the particle distribution as well as measuring the magnetic field created by the magnet. Iron filings obtain the force from nearby virtual magnets. The proposed method is both efficient and robust, and can be used for virtual experiments in elementary and middle schools.
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장태순(Chang, Taesun),김철환(Kim, Chulhwan),황철호(Hwang, Cheolho) 한국소음진동공학회 2012 한국소음진동공학회 논문집 Vol.22 No.11
Transparent noise barrier panels have the advantages of transmitting light to nearby residents and allowing drivers to orientate themselves by providing views of the surrounding area. To develop guidelines on quality criteria for transparent soundproof panels, their sound transmission loss and weatherability were experimentally investigated. In Korea, the sound transmission loss of noise barrier panels should be more than 25 dB at 500 Hz and 30 dB at 1000 Hz. The transmission loss tests of transparent panels were performed in accordance with KS F 2808. Typically, plastic materials suffer from color changes when exposed to ultraviolet(UV) light over extended periods. Therefore, weathering of plastics is one of the most important properties for outdoor applications. Protection against UV radiation and weathering is usually accomplished by using UV stabilizer additives or coatings. Transparent materials for soundproof panels were examined through accelerated weathering tests and their weathering resistances were evaluated from changes in yellowness index.
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