• 대한기계학회논문집A
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• 제30권1호
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• pp.18-25
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• 2006

The purpose of this research work is to demonstrate a successful application of hybrid-mixed formulation and nodeless degrees of freedom in developing a very accurate in-plane curved beam element for free vibration analysis. To resolve the numerical difficulties due to the spurious constraints, the present element, based on the Hellinger-Reissner variational principle and considering the effect of shear deformation, employed consistent stress parameters corresponding to cubic displacement polynomials with additional nodeless degrees. The stress parameters were eliminated by the stationary condition, and the nodeless degrees were condensed by Guyan Reduction. Several numerical examples indicated that the property of the mass matrix as well as that of the stiffness matrix have a great effect on the numerical performance. The element with consistent mass matrix produced best results on convergence and accuracy in the numerical analysis of Eigenvalue problems. Also, the higher-order mixed curved beam element showed a superior numerical behavior for the free vibration analyses.

• Tribology and Lubricants
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• 제36권3호
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• pp.139-146
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• 2020

Global warming has led to an increase in demand of eco-friendly vehicles, such as electric cars, for reducing greenhouse gas emissions, and especially, regulating carbon dioxide generation. In addition, electric vehicles are equipped with an electric drive-type hermetic scroll compressor and a refrigerant, which exhibit current and future trends of using environmentally friendly refrigerants, including R-1234yf. In this study, polyol ester-based refrigeration oils are prepared via condensation esterification of polyol and fatty acids. The oils can be combined with R-1234yf refrigerant for applications in air conditioning and cooling systems of electric vehicles. The structure of synthetic polyol esters is confirmed via ¹H-NMR and FT-IR spectrum analysis, and the composition of the polyol ester is analyzed via gas chromatogram analysis. Furthermore, kinematic viscosity, viscosity index, total acid value, pour point, and color are analyzed as fundamental physical properties of the synthetic polyol esters. The compatibility and chemical stability of the synthetic polyol ester combined with the R-1234yf refrigerant are obtained via high temperature and high pressure oil-resistant refrigerant tests. The changes in the oil color and catalyst activity are observed before and after the experiment to determine whether it is suitable as a refrigerator oil.

• 공업화학
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• 제22권2호
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• pp.196-202
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• 2011

폴리올 에스테르 등의 에스테르 윤활제는 생분해성 및 윤활성능이 우수하여 금속가공유 및 유압작동유등의 윤활기유로 많이 사용되고 있다. 본 연구에서는 윤활성 향상제로 사용하기 위하여 알킬 무수 숙신산과 여러 가지 지방 알콜과의 축합반응을 행하여 알킬 숙시네이트 유도체를 합성하였다. 합성된 알킬 숙시네이트 유도체의 구조는 $^1H-NMR$ 및 FT-IR 스펙트럼으로 분석하였으며 GC 크로마토그램을 통하여 화합물의 순도를 확인하였다. 또한, 합성 유도체의 기본물성으로 점도특성, 굴절률, 전산가, 유동점 등을 측정하였으며 응용물성으로 윤활특성을 SRV 시험기와 4-ball 마모 시험기로 마찰계수(COF) 및 마모흔 직경(SRV WSD 및 4-ball WSD)을 측정하여 평가하였다. 기본물성 평가결과, 점도 특성, 굴절률 및 유동점은 알킬 숙시네이트 유도체에 함유된 알킬기의 탄소수가 증가할수록 높아졌으며 전산가는 0.2~4 mgKOH/g를 나타내어 금속가공유 및 유압작동유의 윤활제로 사용가능함을 알 수 있었다. 윤활성능 평가 결과, SRV WSD 0.391~0.689 mm, SRV COF 값은 0.110~0.138, 4-ball WSD 값은 0.49~0.55 mm를 나타내어 에스테르의 구조에 따라 차이를 나타내었다. 특히, SRV 시험에서 비교물질로 사용된 폴리올 에스테르인 TMPTO와 윤활성능을 비교하였을 때 SRV WSD 결과, 알킬기에 따라 다른 차이를 나타냈지만 비교물질에 비해 비교적 우수한 값으로, SRV COF 결과, 알킬기에 대한 영향을 받지 않고 비교물질에 비해 약간 떨어지는 값을 나타내었다.