• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1996년도 춘계 학술대회논문집
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• pp.40-45
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• 1996

This paper discribes the viscous interaction of Hypersonic Wedge Flows using Roe FDS and AUSM+. For this purpose we developed the frozen and the equilibrium code and numerically simulated the viscous interaction by changing the surface temperature and the mach number. We used curve fitting data in NASA Reference Publication 1181, 1260 to calculate equilibrium properties. We compare the equilibrium flow with the frozen flow. We conclude that the mach number and the surface temperature are significant parameters, as the surface temperature and the mach number increase the viscous interaction becomes stronger, and we must consider high-temperature effects in hypersonic flow

• Journal of Neurogastroenterology and Motility
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• 제24권4호
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• pp.570-576
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• 2018

Background/Aims Swallows with viscous or solid boluses in different body positions alter esophageal manometry patterns. Limitations of previous studies include lack of standardized viscous substrates and the need for chewing prior to swallowing solid boluses. We hypothesize that high-resolution impedance manometry (HRiM) using standardized viscous and super-viscous swallows in supine and upright positions improves sensitivity for detecting esophageal motility abnormalities when compared with traditional saline swallows. To establish normative values for these novel substrates, we recruited healthy volunteers and performed HRiM. Methods Standardized viscous and super-viscous substrates were prepared using "Thick-It" food thickener and a rotational viscometer. All swallows were administered in 5-mL increments in both supine and upright positions. HRiM metrics and impedance (bolus transit) were calculated. We used a paired two-tailed t test to compare all metrics by position and substrate. Results The 5-g, 7-g, and 10-g substrates measured 5000, 36 200, and 64 $700mPa{\cdot}sec$, respectively. In 18 volunteers, we observed that the integrated relaxation pressure was lower when upright than when supine for all substrates (P < 0.01). The 10-g substrate significantly increased integrated relaxation pressure when compared to saline in the supine position (P < 0.01). Substrates and positions also affected distal contractile integral, distal latency, and impedance values. Conclusions We examined HRiM values using novel standardized viscous and super-viscous substrates in healthy subjects for both supine and upright positions. We found that viscosity and position affected HRiM Chicago metrics and have potential to increase the sensitivity of esophageal manometry.

• Earthquakes and Structures
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• 제13권4호
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• pp.337-351
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• 2017

In the present study a capacity spectrum method based on constant ductility inelastic spectra to estimate the seismic performance of structures equipped with elastic viscous dampers is presented. As the definition of the structures' effective damping, due to the damping system, is necessary, an alternative method to specify the effective damping ratio ${\xi}eff$ is presented. Moreover, damping reduction factors (B) are introduced to generate high damping elastic demand spectra. Given the elastic spectra for damping ratio ${\xi}eff$, the performance point of the structure can be obtained by relationships that relate the strength demand reduction factor (R) with the ductility demand factor (${\mu}$). As such expressions that link the above quantities, known as R - ${\mu}$ - Τ relationships, for different damping levels are presented. Moreover, corrective factors (Bv) for the pseudo-velocity spectra calculation are reported for different levels of damping and ductility in order to calculate with accuracy the values of the viscous dampers velocities. Finally, to evaluate the results of the proposed method, the whole process is applied to a four-storey reinforced concrete frame structure and to a six-storey steel structure, both equipped with elastic viscous dampers.

• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.202-208
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• 2017

최근 개발된 선박용 주기관은 추진효율 향상과 연료소비율 저감기술이 요구됨에 따라 과거에 비해 높은 비틀림진동 기진력 특성을 갖고 있다. 따라서 이를 제어하기 위해 기본적으로 엔진 선단에 점성 댐퍼나 점성-스프링댐퍼를 장착한다. 점성댐퍼의 경우 댐퍼 내부에 채워진 실리콘 오일이 탄성적인 연결이 없다고 가정하고 댐퍼설계를 하여 왔으나 고점도 실리콘 오일은 높은 점도에 따른 비틀림 강성이 존재할 뿐만 아니라 작동온도와 주파수에 따라 비선형적인 동특성을 갖는다. 본 논문에서는 고점도 실리콘 오일이 적용된 점성댐퍼의 동특성을 확인하고 해당 댐퍼가 장착된 축계의 비틀림진동 특성을 검토하였다. 이를 위해 점성댐퍼의 최적 동특성을 이론적으로 해석하는 방법을 검토하였고, 고점도 실리콘 오일로 채워진 점성댐퍼로 해당축계의 비틀림진동 제어를 하는 경우 댐퍼 작동온도 및 경년변화를 고려한 추진축계 최적 설계 방안에 대해서 검토하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.24.1-24.1
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• 2005

• 동력기계공학회지
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• 제1권1호
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• pp.98-105
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• 1997

In general, crankshafts which are used in internal combustion reciprocating engines are subjects to high torsional vibration. Therefore, a damper is often used to minimize the torsional vibration in reciprocating engines. In this paper, in order to investigate damping performance of viscous damper, the real effective viscosity and complex damping coefficient of silicone oil, and the effective inertia moment of inertia ring are calculated considering the relative motion between damper casing and inertia ring. Based on these results multi-cylinder shaft is modeled into equivalent 2-degree of freedom system and optimum condition is estimated by calculating the amplification factor of viscous damper. Also the test damper was manufactured according to the result of theoretical investigation, the performance and durability was ascertained through experimental examination.

• 한국가시화정보학회지
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• 제16권2호
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• pp.53-58
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• 2018

This paper presents an electromagnetically driven microrobot for the enhancement of mixing performance in high viscous liquid media such as blood and bone marrow. First, an electromagnetic system was fabricated, and the magnetic flux density generated from the system was compared with the theoretical value. Second, the reciprocating motion of the microrobot was demonstrated in microchannel using electromagnetic system. As a proof of concept, the mixing performance by the electromagnetically driven microrobot in high viscous liquid was investigated using safranin solution. As a result, it was completely mixed within 140 s with the reciprocating motion of the microrobot while it took 1680 s for natural diffusion. In addition, the mixing efficiency was quantitatively evaluated through a mixing index obtained by an image analysis. The proposed method provides not only wireless actuation of a microrobot with a simple design but also high mixing performance in variety of high viscous liquid media.

• 소음진동
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• 제7권5호
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• pp.861-869
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• 1997

An approximate analytical method has been developed for estimating hydrodynamic forces acting on oscillating inner cylinder in concentric annulus. When the rigid inner cylinder executes translational oscillation, fluid inertia and damping forces on the oscillating cylinder are generated by unsteady pressure and viscous skin friction. Considering the dynamic-characteristics of unsteady viscous flow and the added mass coefficient of inviscid fluid, these hydrodynamic forces including viscous effect are dramatically simplified and expressed in terms of oscillatory Reynolds number and the geometry of annular configuration. Thus, the viscous effect on the forces can be estimated very easily compared to an existing theory. The forces are calculated by two models developed for relatively high and low oscillatory Reynolds numbers. The model for low oscillatory Reynolds number is suitable for relatively high ratio of the penetration depth to annular space while the model for high oscillatory Reynolds number is applicable to the case of relatively low ratio. It is found that the transient ratio between two models is approximately 0.2~0.25 and the forcea are expressed in terms of oscillatory Reynolds number, explicity. The present results show good agreements with an existing numerical results, especially for high and low penetration ratios to annular gap.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.59-63
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• 2001

A high-impulse, low-power, continuous-shot microthruster has been developed using low boiling temperature liquid-propellant with high viscous fluid-plug. The viscous friction force of the fluid-plug increases the blast pressure and the low boiling temperature liquid-propellant is intended to reduce input power consumption. The three-layer microthruster has been fabricated by surface micromachining as well as bulk micromachining in the size of $7{\times}13{\times}1.5mm^{3}$. A continuous output impulse bit of $6.4{\times}10^{-8}N{\cdot}sec$ has been obtained from the fabricated microthruster using perfluoro normal hexane (FC72) propellant and oil plug, resulting in about ten times increase of the impulse bit using one hundredth electrical input energy compared to the conventional continuous microthruster.

• 동력기계공학회지
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• 제13권5호
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• pp.11-17
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• 2009

A numerical study of unsteady mixed convection in a cavity with high viscous fluid is presented. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Rayleigh number ($10^3\;{\leq}\;Ra\;{\leq}\;10^5$), the Reynolds number (0 < Re $\leq$ 1), and the aspect ratio (0.5 $\leq$ AR $\leq$ 2). The fluid used is silicon oil, a high prandtl number fluid, Pr = 909.1. The results show velocity vectors and temperature distributions. It is found that the periodic flows in a cavity are observed at very low Reynolds numbers, and the period of periodic flow decreases with increasing Reynolds and Rayleigh numbers, and increases with increasing aspect ratio. Also, the Reynolds number range of periodic flow increases with increasing Rayleigh numbers and aspect ratio.