• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.762-767
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• 2007

As a macromolecule material, melted rubber flow shows characteristics of shear thinning fluid. The dynamic viscosity of this rubber fluid is influenced by temperature and shear strain rate. In this study, the numerical simulation of rubber extrusion forming process has been performed using commercial CFD code, Polyflow. Power-law model considering the effect of shear rate is used for the computer simulation of this non-Newyonian flow. Also Non-isothermal behavior is considered as Arrhenius-law model. Distributions of velocity and temperature are predicted through the simulation.

• Journal of Microbiology and Biotechnology
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• 제7권4호
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• pp.282-286
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• 1997

The floc strength of Escherichia coli was enhanced by adding water soluble polymer flocculants (BPA-5020 and BPA-5000) to the particulate flocculant (BPA-1000) as indicated by the increase in the shear index. The shear index of the E. coli flocs increased from 0.39 with the particulate flocculant alone to 0.94 with the particulate flocculant in conjunction with the water soluble polymer flocculant. In addition, the sedimentation rate of flocs was higher and the sedimented volume of flocs was smaller when the particulate flocculant was used with the water soluble polymer flocculant. When E. coli was flocculated first with the water soluble flocculant and the particulate flocculant was added later into the E. coli flocs formed, the sedimentation rate of the flocs was greater than that of any other combination. The shear index of the flocs was, however, independent of the sequence of the flocculant addition.

• Korea-Australia Rheology Journal
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• 제18권4호
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• pp.191-197
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• 2006

The measurement of the compressional rheological parameters for an aggregated particulate suspension is described. The parameters include the compressive yield stress and hindered settling function, describing the extent and rate of dewatering respectively. The variation of these parameters with shear rate and time of shear is also considered in the light of their sensitivity to low shear rates, with particular reference to the case of flocculated particulate suspensions. The latter is seen to be important in the future development of a comprehensive understanding of compressive rheology of aggregated particulate suspensions in industrial applications such as thickening, filtration and centrifugation.

• 대한기계학회논문집
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• 제19권9호
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• pp.2297-2307
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• 1995

An experimental study on the structure of a separated shear layer downstream of the backward-facing step has been performed by examining mean flow and turbulent quantities in terms of free stream turbulence. When free stream turbulence exists, the entrainment rate of the separated shear layer and the flow rate in the recirculation region are enhanced, resulting in shorter reattachment length. The production and diffusion terms in the turbulent kinetic energy balance are shown to increase more than the dissipation term does. Rapid decrease of the pressure-strain term in the shear stress balance implies the enhancement of the three-dimensional motion by free stream turbulence.

• Archives of Pharmacal Research
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• 제19권3호
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• pp.183-190
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• 1996

There are a wide variety of semi-solid ointments used for healing the skin diseases, whose therapeutic and skin penetration abililties may greatly differ from one another depending on the compositions of ointment vehicles. A computer optimization technique was applied to obtain the optimum formula of o/w type ointment giving the in vitro maximum absorption rate through hairless rat skin membrane. Some of the formulations were selected to find out a relationship between skin penetration of ointment and its Theological characteristics. The experimental value of absorption rate obtained from the ointment by optimum formula agreed well with the theoretical value obtained from a polynomial regression analysis, Three kinds of ointments selected among 15 formulations were obtained with a concentric cylinder type rheometer (Model; Rheolab SM-HM Physica, Germany) at 20, 30, 40 and $50^{\circ}C$ for rheograms of rhelolgical properties of o/w type ointments. As the temperature was raised, all products showed a decrease in both shear stress and yield values. The higher skin penetration, the lower shear stress showed.

• 한국분무공학회지
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• 제26권1호
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• pp.9-17
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• 2021

Six shear coaxial injectors with different recess length and taper angle were manufactured. Cold-flow tests on the injectors were performed at room temperature and pressure using water and air as simulants. By changing the water mass flow rate and air mass flow rate, spray images were taken under single-injection and bi-injection. Breakup length and spray angle were analyzed from instantaneous and averaged spray images using image processing techniques. For all the injectors, the breakup length generally decreased as the momentum flux ratio increased at the same gas mass flow rate. The injectors with 7.5° taper angle usually had the longest breakup length and the smallest spray angle. When the taper angle was 15° or more, it hardly affected breakup length and spray angle. The recess length did not influence breakup length but its effect on spray angle depended on the taper angle.

• 한국지반환경공학회 논문집
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• 제18권2호
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• pp.29-37
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• 2017

집중호우로 인하여 산악지반에 발생하는 토석류의 거동은 대상지반 세립분의 전단강도 및 유변학적 특성들에 의하여 영향을 받기 때문에, 두 특성에 대한 정수는 토석류 거동을 파악하는데 매우 중요한 요소이다. 본 연구에서는 직접전단 실험을 통하여 세립분의 전단강도 및 유변학적 정수를 평가하고자 하였다. 건조상태와 액성한계상태로 조성된 두 가지 세립분 시료에 대하여 직접 전단실험을 수행하였으며, 연직응력에 따른 전단강도를 측정하여 점착력과 내부마찰각을 산정하였다. 또한 액성한계로 조성된 시료의 잔류전단강도를 획득하기 위하여 전단변형률속도와 전단방향을 변화시켜 반복전단실험을 수행하였다. 실험 결과, 액성한계상태의 시료는 건조 상태 시료에 비해 내부마찰각은 작지만 점착력은 더 큰 것으로 나타났으며, 잔류전단강도를 통해 산정한 내부마찰각과 점착력은 첨두전단강도에 의해 산정된 결과보다 작은 것으로 나타났다. 반복전단 결과, 전단변형률속도와 잔류전단강도는 선형적인 관계를 보였으며, 전단변형률속도-잔류전단강도 관계의 기울기로써 결정되는 점성은 약 $73.60Pa{\cdot}s$로 산정되었다. 본 연구는 직접전단 장비가 산악지반 토석류 거동과 관련된 세립분의 전단강도 및 유변학적 정수 산정에 효과적으로 활용될 수 있음을 보여준다.

• 한국지반공학회논문집
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• 제30권7호
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• pp.5-15
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• 2014

휴 폐광산지는 산발생, 지하수 오염뿐만 아니라 침식 및 산사태 등 다양한 물리화학적 지질재해에 노출되어 있다. 임기광산 폐석적치장 광미를 대상으로 링 전단시험을 수행하여 전단속도에 따른 전단특성을 조사하고 한다. 본 연구에 있어 마찰저항을 최소화할 목적으로 링 전단상자 오링(O-ring)은 전단동안 회전이 가능하도록 설계되었다. 1차 시험은 일정한 수직응력(50kPa)과 전단속도(0.1mm/sec) 조건에서 전단시간에 따른 전단응력을 조사하였다. 2차 시험은 일정한 수직응력 조건에서 전단속도를 0.01, 0.1, 1, 10, 50, 100mm/sec로 순차적으로 증가시켜 전단속도에 따른 전단응력을 조사하였다. 3차 시험은 일정한 전단속도(0.1mm/sec)하에서 수직응력을 20, 40, 60, 80, 100, 150kPa로 증가시켜 각 경우에 대한 전단응력을 조사하였다. 시험결과에 따르면, 배수조건에 관계없이 임기광산 폐석적치장광미시료는 전단연화거동(strain softening behavior)을 보였다. 특히 전단속도가 10mm/sec보다 작은 경우 잔류전단응력은 100~300초 사이에 일정한 값에 도달하는 것으로 나타났다. 2차와 3차 시험결과에 따르면, 배수조건에 관계없이 전단응력은 전단속도와 수직응력의 함수로 나타났다. 하지만, 배수조건에 따라 링 전단상자 전단부에서 상이한 입자파쇄 특성이 관측되었다. 배수조건시 전단상자 전단면에서 하단까지 넓은 전단띠가 형성된 것에 반해, 비배수조건시 전단면에 국부 전단띠가 형성되었다. 이러한 점에 비추어 볼 때, 전단속도에 따른 입자파쇄 특성은 산사태 유동성을 높이는 중요한 인자로 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 가을 학술발표회 논문집
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• pp.184-189
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• 1993

This is an experimental investigation the shear behavior of reinforced concrete with stirrup of which stress ranges 0.0㎏/㎠ to 7.0㎏/㎠. Five rectangular beams which concrete strengths are 287㎏/㎠ and 380㎏/㎠, a/d=3, and main steel ratio equal to 1.96% was tested. Those were designed to fail in shear. The shear cracking load and failure load were measured and compared with ACI's equation and Zutty's proposed equation. The results are following : ACI equation and Zutty's equation are consertive. As the concrete compressive strength increased, reserved shear strength of beams with minimum web reinforcement decreases. According to increase of web reinforcement , the rate of increases of shear strength is decreased. The failure modes of specimen with minimum web reinforcement are shear compression failure which is reached after diagonal shear cracking.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.884-889
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• 2003

Based on the reinterpretation of the well-known relationship between shear and the rate of change of bending moment in a reinforced concrete beam subject to combined shear and moment loads, the shortcomings of present truss models are discussed. The core of the theory is that a new perspective on the shear strength can be gained by viewing the internal stress filed in terms of the superposition of two base components of shear resistance; arch action and beam action. The arch action can be designed using the simple truss having curved compression chord, while the beam action between the two chords can be modeled using a parallel chord truss with MCFT or RA-STM. The compatibility of deformation associated to the two action is taken into account by employing a characteristic factor a. The new model was examined by the Stuttgart beam shear tests, and the results show that the present approach provides good estimates of stirrup contribution and concrete contributions.