• Geomechanics and Engineering
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• 제5권5호
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• pp.401-417
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• 2013

The results of an experimental program regarding the effects of gradation on shear strength and volume change behavior of silty sands are presented. Consolidated drained direct shear tests were performed on two clean base sands and twelve silty sands obtained by mixing those base sands with two different non-plastic silts at various fines contents (${\leq}$ 25%). Drained shear strengths were observed to be not significantly influenced by either base sand gradation or silt gradation or fines content for the studied range. Increasing fines content has increased the volumetric contraction of specimens at similar void ratio. However, the amount of increase in volumetric contraction of silty sands were found to be affected by silt gradation when other influencing factors such as fines content, base sand gradation and mineralogy were kept the same. Moreover, the amount of increase in volumetric contraction of silty sands were also found to be affected by base sand gradation when other influencing factors such as fines content, silt gradation and mineralogy were kept the same.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.178-183
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• 2000

Electrorheological(ER) effect on the dispersive system of polarizable fine powder/dielectric oil has been investigated. The electrical and rheological properties of zeolite and starch based ER fluid were reported. The ER fluids were constructed by mixing zeolite and starch power with two different dielectric oils. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields, particle concetrations, and temperatures. The electric field is applied by high voltage DC power supply. The outer cup is connected to positive electrode(+) and the bob becomes ground(-). And the temperatures the viscosity(or shear stress) versus shear rates were measured. In this experiment shear rates were increased from 0 to $200s^{-1}$ in 2 minutes.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.224-228
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• 2002

To study the trafficability on soft and cohesive benthic terrain, a soil bin is designed and constructed. The information of shear strength of pacific seafloor and the results of dimensional analysis of vehicle-train system are used as basic datum for concept design of soil bin. Cohesive benthic terrain is modeled by means of bentonite-water mixture. The shear strength of the mixture is measured by motorized shear meter. Several facilities are constructed for mixing and evening modeled soil, transporting vehicle model. The shear strength in soil bin is investigated for depth, age and velocity. The result of this study is used as basic information to the experiment, study for development of crawler on benthic terrain.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.21-26
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• 2007

This study focuses on the near-field vortical structure and dynamics of coaxial jets. The characteristics of laminar flow and mixing in coaxial jets are investigated using a unsteady flow simulation. In order to analyze the geometic effects on the vortical structure, several cases of different configurations are selected for various values of the velocity ratio of inner jet to outer jet. From the result, it is confirmed that mixing is promoted by the development of vortical structure and the interaction between inner jet and outer jet. This feature is strongly related to the vortex frequency in the shear-layers. The vortex frequency depends on the velocity ratio and the lip thickness of inner nozzle, but the outer pipe length has no effect on the frequency variation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.221-224
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• 2002

A technique of mixing enhancement in an underexpanded sonic round jet is studied with fully expanded jet Mach number 1.5. Tonal sound, jet screech can be produced at some underexpansion pressure ratio in a sonic jet. Since the jet screech excites the initial Jet shear layer to change the flow, a reflector which focuses the jet screech near the nozzle lip is designed. The reflector has an elliptic shape of which two foci are located near the nozzle lip and the jet screech source region. Jet screech tone near the nozzle lip increases with the elliptic reflector and spreading of the jet largely increases. It is concluded that mixing enhancement of the jet with the elliptic reflector is attributed to large scale structures which are initially excited by the increased jet screech.

• 한국전산유체공학회지
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• 제14권3호
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• pp.49-55
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• 2009

This study focuses on the near-field vortical structure and dynamics of coaxial jets. The characteristics of laminar flow and mixing in coaxial jets are investigated using a unsteady flow simulation. In order to analyze the geometric effects on the vortical structure, several cases of different configurations are selected for various values of the velocity ratio of inner jet to outer jet. From the result, it is confirmed that the flow mixing is promoted by the development of vortical structure and the interaction between inner jet and outer jet. This feature is strongly related to the vortex frequency in the shear-layers. The vortex frequency depends on the velocity ratio and the lip thickness of inner nozzle, but the outer pipe length has no effect on the frequency variation.

• 한국정밀공학회지
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• 제9권4호
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• pp.109-117
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• 1992

Mixing of ceramic-binder system was investigated experimentally and theoretically for application to Ceramic Injection Molding. Polypropylene, stearic acid, and paraffin wax were selected as the binder system, and silicon nitride fine powders were selected as the ceramic material. Single screw ectruder was employed as the mixing equipment. Theoretical analysis was performed to investigate the mixedness of mixture quantitatively. The analysis predicted average residence time average total strain, and average shear stress as a function of screw speed for mixtures of different volume fraction. Qualitative mixedness of mixture and characteristics of mixing were investigated by using SEM and EPMA. In addition, rheological properties of the mixture were investigated by using a capillary rheometer to examine possibility of injection molding.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1247-1252
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• 2014

본 연구에서는 온도조건에 따른 MR 유체의 물리적 특성을 연구하고자 침전 및 전단응력실험을 수행하였다. MR 댐퍼에 사용되는 MR 유체는 자성 파우더를 포함하고 있어 침전현상이 발생하므로 침강성과 인가전류에 의한 전단응력 변화를 상온과 고온조건에서 실험하였다. 침강특성을 조사하기 위하여 강제 대류형 오븐을 인가전류에 의한 전단응력을 측정하기 위하여 점도계를 사용하였다. 실험결과로부터 MR 유체는 시간과 온도에 따른 침강 특성이 다름을 그리고 교반시간이 큰 경우에 MR 유체의 분산성이 2배 이상 우수하였다. 전단률이 증가할수록 전단응력은 로그함수의 증가분포를 인가전류를 증가할수록 2차 함수의 증가분포를 그리고 MR 유체의 전단응력은 상온보다 고온에서 6-18% 낮은 분포를 보였다.

• 한국산학기술학회논문지
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• 제13권10호
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• pp.4385-4391
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• 2012

본 연구는 전단혼합과 초음파 처리를 통해 충전재의 분산을 증대시켜 복합재료 시편을 만들고, 분산의 적정성을 판단하기 위해서 주사전자현미경 이미지를 이용하며, 인장실험을 통해 기계적 물성치를 측정하고 고찰하였다. 초음파 처리와 전단혼합 시간 증가를 통해서 개선된 공정으로 만들어진 시편의 경우, 충전재 분산에 대한 정성적인 평가인 SEM 이미지와 정량적인 평가인 인장시험 데이터의 상호 보완을 통해 충전재의 복합재료 수지 내에서의 적절한 분산 여부를 판단할 수 있었다. 인장강도의 측정 결과에서는 충전재가 함유된 모든 시편이 Pure Epoxy 시편 보다 높은 인장 강도를 보였는데, 충전재 0.6wt%에서 가장 높은 인장강도 값을 나타냈다. 0.9wt%와 1.2wt% 시편은 Pure Epoxy 시편보다는 인장강도가 증가하였지만 0.6wt% 시편보다 작은 값을 보였다. 인장강성 측정 결과는 충전재의 함유량이 높아질수록 증가하는 결과를 보였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.61-67
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• 2010

Thick soft clay deposits which are generally located at the west and south coast of the Korean peninsula have complicated characteristics according to their orientation and formation history. Thus, several geotechnical problems could possibly occur when those soft clay deposits are used as foundations for marine structures. Deep cement mixing (DCM) method is one of the most widely used soft soil improvement method for various marine structures, nowadays. DCM method injects binders such as cement into the soft ground directly and mixes with the in-situ soil to improve the strength and other geotechnical properties sufficiently. However, the natural impacts induced by dynamic motions such as ocean waves, wind, typhoon, and tusnami give significant influences on the stability of marine structures and their underlaying foundations. Thus, the dynamic properties become important design criteria to insure the seismic stability of marine structures. In this study, the dynamic behavior of cemented Busan clay is evaluated. Laboratory unconfined compression test and resonant column test are performed on natural in-situ soil and cement mixed specimens to confirm the strength and strain-dependent dynamic behavior variation induced by cement mixing treatment. Results show that the unconfined compressive strength and shear modulus increase with curing time and cement content increment. Finally, the optimized cement mixing ratio for sufficient dynamic stability is obtained through this study. The results of this study are expected to be widely used to improve the reliability of seismic design for marine structures.