• The Korean Journal of Rheology
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• v.11 no.1
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• pp.1-8
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• 1999

This paper experimentally investigates the steady shear behaviors of electro-rheological(ER) fluids under flow mode at high pressure level. As for the ER fluid to be tested, two types of ER fluids are employed; water-based ER fluids (ERF 1, ERF 2) and water-free ER fluid(ERF 3). The water-based ER fluids are composed inhousingly, and the concentrations of dispersed particles are 20 wt% and 30 wt% for ERF 1 and ERF 2, respectively. To generate the flow mode at high pressure, an experimental apparatus operated by two-way hydraulic cylinder is constructed and utilized. The pressure difference is measured by the pressure sensor, while the flow rate is calculated using the measured data of the displacement sensor(LVDT). Consequently, the shear stress and shear rate are distilled by incorporating the measured data; the pressure difference and the flow rate.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.1
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• pp.25-34
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• 2000

A panoramic-PIV technique is employed to characterize the travelling tip vortices and the profile of oil-water Interface in the tandem fence arrangement. Instantaneous as well as time-averaged velocity profiles of the water layer close to the interface were obtained to evaluate the possibility of measuring the shear stress distribution on oil-water interface. It was proven that the present technique could provide some qualify data precise enough to resolve detailed flow structures inside a shear layer formed on oil-water interface provided it is nearly stationary.

• The Korean Journal of Rheology
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• v.11 no.2
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• pp.143-152
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• 1999

Using a Rheometrics Fluids Spectrometer(RFS II), the steady shear flow and the small-amplitude dynamic viscoelastic properties of three kinds of semi-solid food materials(mayonnaise, tomato ketchup, and wasabi) have been measured over a wide range of shear rates and angular frequencies. The shear rate dependence of steady flow behavior and the angular frequency dependence of dynamic viscoelastic behavior were reported from the experimentally measured data. In addition, some viscoplastic flow models with a yield stress term were employed to make a quantitative evaluation of the steady flow behavior, and the applicability of these models was also examined in detail. Furthermore, the correlations between steady shear flow(nonlinear behavior) and dynamic viscoelastic(linear behavior)properties were discussed using the modified power-law flow equations. Main results obtained from this study can be summarized as follows : (1) Semi-solid food materials are regarded as viscoplastic fluids having a finite magnitude of yield stress, and their flow behavior shows shear-thinning characteristics, exhibiting a decrease in steady flow viscosity with increasing shear rate. (2) The Herschel-Bulkley, Mizrahi-Berk, and Heinz-Casson models are all applicable to describe the steady flow behavior of semi-solid food materials. Among these models, the Heinz-Casson model has the best validity. (3) Semi-solid food materials show a stronger shear-thinning behavior at shear rate region higher than a critical shear rate where a more progressive structure breakdown takes place. (4) Both the storage and loss moduli are increased with increasing angular frequency, but they have a slight dependence on angular frequency. The elastic behavior is dominant to the viscous behavior over a wide range of angular frequencies. (5) All of the steady flow, dynamic, and complex viscosities are well satisfied with the power-law model behavior. The relationships between steady shear flow and dynamic viscoelastic properties can well be described by the modified forms of the power-law flow equations.

• Geotechnical Engineering
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• v.8 no.2
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• pp.71-80
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• 1992

A new constitutive model is proposed for normally consolidated clays. A main skeleton of the proposed model is based on the concepts of the incremental stress-strain theory by Roscoe and Poorooshasb. The equation of the undrained stress path is formulated by introducing the new pore pressure parameter(C), which is the slope of the linear line in the plot of the normalized pore pressure against the stress ratio. Once the stress increment along the constant stress ratio path (followed by untrained stress path) is know, the volumetric strains are calculated from the linear characteristics between void ratio and logarithm of the mean normal stress for any stress ratio. Then the incremental shear strains are successfully predicted by applying the flow rule derived in the modified theory by Roscoe and Burland.

• KSBB Journal
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• v.24 no.6
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• pp.563-569
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• 2009

Fibroin is an insoluble structural protein from Bombyx mori. It can be solubilized by dissolving in a hot $CaCl_2$ solution and subsequent dialysis. The aqueous solution is unstable and a transition from aqueous fibroin molecules rich in random coil is undergo to one rich in $\beta$-sheet content, resulting in hydrogelation. However, fibroin gel is so fragile and plastic that its mechanical property should be reformed for various applications. In this report, a semi-solid form of fibroin gel was prepared using glycerol and ethanol and was investigated to analyze their flow properties. A fibroin gel with 80% glycerol showed pseudoplastic and thixotropic properties. The square root of its yield stress varied linearly with fibroin concentration and it extrapolated to zero shear stress at 0.2% fibroin. A fibroin gel with 40% ethanol was shown to be highly thixotropic but its shear-thinning behavior was only observed above a certain level of shear rate. Its pseudoplasticity was restored by a high rate of shear stress.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.356-361
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• 2011

The flow characteristics of synthetic jet depending on rectangular and circular jet exit configuration are investigated using numerical computation with cross flow. In rectangular slot, synthetic jet generates the strong vortex, however, supply fewer momentum and effectiveness of flow control is reduced along flow direction. In circular slot, regular vortex is fanned from slot center to end and developed in flow direction. It affects the wider region than rectangular slot. The distribution of wall shear stress is considered in order to indicate the effectiveness of flow control device for flow separation delay. As a result, circular slot is a more suitable candidate for delaying flow separation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.947-958
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• 1986

물-증기 역류 성층이상유동에서의 평균 액체층 두께가 여러가지 경사각과 종횡비에 따라 측정되었다. 난류유동에 있어서 전단응력분포의 선형화와 von Karman의 혼합길이 이론을 근거로 평균 액체층의 두께에 대한 관계식이 제시되었으며 실험결과와 잘 일치하였음을 보였다. 접촉면에서의 조파저항이 고려되지 않은 해석결과는, 수평 성층유동의 경우에, 평균 액체층 두께보다는 오히려 파곡까지의 액체층 두께를 예측하고 있는 것으로 나타났다. 또한 평균 액체층 두께에 대한 실험 상관관계식이 계산시 편의를 위해 쉽게 인지할 수 있는 매개변수들의 항들롤 제시되었다.

• Water for future
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• v.23 no.1
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• pp.119-127
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• 1990

The concentration of cohesive suspended sediment is determined by the circulation of water and the material dispersion. The equations of the two-dimensional, depth-integrated dispersive transport are the Reynolds equation, continuity equation, and advection-dispersion equation based on the Fick's law. A finite difference method has been applied to two models of circulation and dispersion transport. The circulation model is solved by the explicit scheme and the dispersion transport model is solved by multi-operational scheme. It is investigated wheter advective terms are included when the equation of circulation is applied to the model. For advection-dispersion equation, it was also investigated about variations of suspended sediment concentration with respect to the critical shear stresses.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1175-1188
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• 1988

Linear estimation in isotropic turbulence is examined to approximate conditional averages in the form of fluctuating velocity fields conditioned on local velocity. The conditional flow fields and their associated vorticity field are computer using experimental data [Van Atta and Chen] and energy spectrum model [Driscoll and Kennedy]. It appears that ring vorticies could be the dominant structure. Due to the extremely large vorticity in the viscous region of a conditional ring vortex, the energy spectrum model can be used appropriately by changing the Reynolds number. The hairpin vortex could be detected by combining vorticies in isotropic field with an anisotropic orientation imbedded in uniform mean shear flow and this is consistent with other studies [Kim and Moin].

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.24-24
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• 2021

자연하천 바닥 경계층 내에서는 복잡한 난류 구조가 형성되며 이들은 하상에 강한 모멘텀을 전달한다. 바닥 부근에 분포하는 유사 입자들은 경계층 내에서 발생한 난류 흐름으로부터 모멘텀을 전달받아 소류사 혹은 부유사 형태로 이송되게 되며, 이러한 유사 이송 과정을 역학적으로 설명하기 위해서는 경계층 내 유체 흐름에 대한 이해가 선행되어야한다. 경계층 내 난류 흐름 특성이 유사 입자의 움직임에 미치는 영향에 대해 분석하기 위해서는 바닥 경계층 내 고해상도 유속 자료와 유사 움직임을 동시에 포착할 수 있는 기술이 요구된다. 하지만 현재까지 수행된 대부분의 선행 연구들은 점 유속을 측정할 수 있는 음파 도플러 유속계 (Acoustic Doppler Velocimetry) 혹은 2차원 입자 영상 유속계를 활용하였으며, 이들은 복잡한 3차원 난류 흐름 특성을 분석하기에는 한계가 있다. 본 연구의 목적은 실험실 실험을 통해 바닥 경계층 내 3차원 난류 흐름이 유사 이송에 미치는 영향에 대해 조사하는 것이다. 본 연구에서는 유사 주변에서의 고해상도 3차원 흐름 유동장 및 순간적인 유사 움직임에 대해서는 합성 개구 (synthetic aperture) 기반의 3차원 입자 영상 유속계 및 입자 추적 유속계를 활용하여 취득하였다. 취득된 흐름 유동장을 기반으로 레이놀즈 전단응력을 산정하였으며 이를 통해 유체가 하상에 미치는 모멘텀의 크기를 파악하였다. 복잡한 난류 흐름 구조에 대해서는 팔분원 분석 (octant analysis)을 통해 구분했으며, 유사가 움직이는 순간의 유속장을 기반으로 유사 이송을 발생시키는 지배적인 난류 흐름 특성에 대해 규명하였다. 본 연구는 바닥 경계층 내 복잡한 3차원 난류 흐름과 유사 입자의 움직임을 동시에 분석함으로써 기존에 수행되어왔던 선행 연구들의 한계점을 극복하고 보다 명확한 유사 이송의 발생 원인에 대해 분석했다는 점에 의의가 있다.