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고승빈,송시몬 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11
Keeping pace with the current rapid development of clean energy, hybrid cars and electric vehicles are receiving extensive attention. Inelectronic control brake systems, which are essential to these vehicles, a solenoid valve is used to control the hydraulic pressure, whichboosts the driver’s braking force. However, strong cavitation occurs at the narrow gap between the ball and seat of a solenoid valve dueto sudden decreases in pressure, leading to severe damage to the valve. In this study, we numerically investigate cavitation in a solenoidvalve to discover geometric parameters that affect cavitation, and we develop an optimal design to minimize the cavitation using an optimizationtechnique. As a result, we propose two design guides for the solenoid valve subject to cavitation: the ratio of the narrowest gaparea to the inlet area and the narrow gap length. We also find that preventing a sudden reduction of a flow passage is important to reducingcavitation. Finally, using an evolutionary algorithm for optimization we minimize cavitation. The optimal design results in a maximumvapor volume fraction of 0.051, compared to 0.74 for the reference model.
이지수,고승빈,조지현,송시몬 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3
Magnetic resonance velocimetry (MRV) is a versatile flow visualization technique that has been utilized for medical applications. Recently, MRV has been used to visualize engineering flows, but most engineers are still unfamiliar with the technique. In this paper, we introduce the basic principles and experimental configurations of MRV in detail and evaluate the accuracy of MRV applied to measure the mean velocity fields of turbulent flows in a circular pipe. A Philips Achieva 3.0 T Tx MRI scanner is used to provide a magnetic field and acquire resonance signals for flow visualization. Fully developed turbulent flows with Reynolds numbers of 6800, 9900 and 19400 were measured, and the axial mean velocity vectors were obtained with a spatial resolution of 0.5 mm for the three directions. Results show that the mean velocity profiles are in good agreement with reference data sets when properly scaled in both the inner and outer layers.
자기공명유속계를 이용하여 예측한 벽면전단응력의 정확도 평가 기준 개발
이지수(Jeesoo Lee),고승빈(Seungbin Ko),양병권(Byungkuen Yang),조지현(Jee-Hyun Cho),송시몬(Simon Song) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Wall shear stress (WSS) exerted on a blood is one of the key factors associated with cardiovascular diseases. It has been found that magnitude and temporal oscillation of WSS can be correlated with atherosclerosis, aortic dilatation and vascular remodeling. Magnetic resonance velocimetry (MRV) is currently the most advanced technique that can noninvasively estimate temporal and volumetric distribution WSS in vivo. Numerous clinical studies have been reported which determined WSS in various vascular region based on MRV measurements. However, it is difficult to discover the descriptions about the absolute accuracy of WSS in literatures, especially in clinical studies because the true value of WSS is unknown. Therefore, a facile criterion for assessing the accuracy of estimated WSS for MRV measurements with unknown WSS would be valuable. In this research, we propose a novel criterion called Reynolds resolution to assess the absolute accuracy of WSS estimated from MRV data. It is described with measurement parameters and thus, can readily be calculated. We investigated the relation between the Reynolds resolution and WSS accuracy by measuring pressuredriven laminar circular tubing flows and a proportional relation was found indicating that the Reynolds resolution could have its potential to be used for predicting the absolute errors of MRV-estimated WSS.