• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1994.06b
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• pp.19-29
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• 1994

Since Winslow (1) has reported an electro - theological (ER) effect which features remarkable and reversible changes in the properties of the fluid due to an imposed external electric field, numerous applications of ER fluids in mechanical devices, such as clutches, control valves, active dampers, and etc. have been proposed to improye dramatical ly their performances (2,3). When the external electric field is imposed to the ER fluid, it behaves as a Bingham fluid, displaying a field dependent yield shear stress which is widely variable. Without the electric field, the ER fluid has a reversible and constant viscosity so that it flows as a Newtonian fluid. Another salient feature of the ER fluid is that the time required for the variation is very short (< 0.001 sec) (4-6). These attractive.characteristics of the ER fluid provide the possibility of the appearance of new engineering technology , for instance, an active vibration control system. Recently, the application of the ER fluid to rotor-bearing systems has been also initiated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.882-889
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• 2002

This paper presents vibration control performance of a squeeze mode ER mount for high static load. After experimentally investigating the field-dependent damping force under the squeeze mode motion, a squeeze mode ER mount which can support 200 kg of static load is designed and manufactured. Displacement transmissibility of the proposed ER mount is experimentally evaluated in frequency domain with respect to the intensity of the electric field, and a sky-hook control algorithm is designed to attenuate unwanted vibration. Vibration isolation capabilities of the flow mode ER mount and rubber mount are compared to those of the proposed squeeze mode ER mount.

• Advances in Energy Research
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• v.3 no.2
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• pp.125-131
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• 2015

Prompt neutron lifetime calculations have been performed for the NIRR-1 reactor HEU and LEU cores using the 1/v insertion and the Adjoint flux weighing methods. Results of calculations obtained for the HEU and LEU cores are respectively $57.3{\pm}0.8$ and $47.5{\pm}0.7$ for the 1/v insertion and $56.9{\pm}0.3$ and $46.3{\pm}0.5$ for the Adjoint flux. There is a good agreement seen between the two methods for both cores. The prompt neutron lifetime was observed to be shorter in the LEU than for the HEU as expected. However, the Adjoint flux weighing method seemed to be the easiest method in calculating the prompt neutron lifetime for NIRR-1.

• Journal of Species Research
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• v.11 no.3
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• pp.194-201
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• 2022

Species of the genus Eopompilus Gussakovskij, 1932 from South Korea are reviewed. Three species are confirmed: E. internalis, E. luteus, and E. minor. Eopompilus luteus is recorded for the first time in Korea, and is easily separated from its congers by markedly extensive coloration and comparatively large body size in both sexes. Females are characterized by yellowish wing, light brown stigma and veins, lacking of subapical or apical dark fascia on forewing. Males are characterized by serrate antenna formed by submesal convex on each flagellomeres 2-11, symmetrical claws of fore tarsus, hypopygium widened basally and forming a rhomboid plate, lacking of dark fasciae in forewing. The specimen identified as Cryptocheilus nicevilli Bingham from Korea by Kim (1970) is examined and is reclassified as conspecific with E. luteus. A key is presented of the three species complemented by digital images and diagnosis.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.208-217
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• 1998

본 연구에서는 ER 브레이크와 ER클러치를 피드백작동기로 사용하여 이송테이블의 위치 추적제어를 수행하였다. 이를 위해 먼저 아라빅 검(arabic gum)계통의 ER유체를 자체조성한 후 전기장에 대한 빙햄(Bingham)모델을 실험적으로 도출하였다. 빙햄모델에 근거하여 평판형의 ER브레이크와 실린더형의 ER클러치를 설계 제작하였으며, 계단입력(step input)전기장에 따른 출력토오크특성을 통하여 이들 작동기의 동적모델을 얻었다. 이들 작동기와 연계된 이송테이블시스템의 운동지배방정식을 유도한 후 위치추적제어를 위한 슬라이딩모드제어기를 설계하였다. 제어기 설계시 이송해이블의 부하질량 변화에 대한 시스템 불확실성과 마찰력을 고려하여 제어성능의 강건성을 보장하도록 하였다. 제안된 제어시스템의 제어영역(control bandwidth)을 주파수 영역에서 고찰한 후 여러 레적에 대한 위치추적제어 실험을 수행하였다.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.81-92
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• 2011

The rheological properties of Wyoming bentonites are strongly influenced by the size of particles, cation exchangeable capacity, arrangement and morphology of clay mineral. This paper presents the results of rheological investigations on the Wyoming bentonites aqueous dispersions: two types of particle flocculation were considered. For the Wyoming bentonite, 0g/L and 30g/L NaCl equivalent salinity were added in fresh and salt water to examine the rheological behavior. This paper examined the general rheological characteristics, compatibility of rheological models and correlation between soil structure and change in rheological properties of Wyoming bentonite caused by increasing salinity. From flow curves of bentonites hydrated with fresh water and salt water, the observed general flow behavior is very close to shear thinning with yield stress (or ideal Bingham fluid with yield stress and plastic viscosity). However, the change of shear stress at the same shear rate is clear, particularly for lower shear rate. Well-known rheological models are used to fit the data. There is a good agreement between rheological model and data: Carreau, Herschel-Bulkley and power-law for S=0g/L and bilinear, Herschel-Bulkley and power-law for S=30g/L. It may be due to the fact that the internal structural bonding (strong modification of particle-particle interactions from edge-to-edge and/or edge-to-face to face-to-face) in soil matrix is affected from the evolution of rheological properties with different salinities.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.92-97
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• 2011

Landfill is the main treatment method for bottom-ash because it has not only an irregular particle size and ingredients but also not proper recycling treatment. The aim of this study is to raise recycling rate of bottom-ash(nonplasticity pulverulent) and for the purpose of alternatives of clay to investigate the properties of Bottom-ash (B/A)-Hard Clay (H/C) bodies with controlled interfacial chemistry properties. After investigating the sedimentation height of suspensions with controlled pH, it was discovered that there was no hetero-polar aggregation for mixed slips because hard clay and bottom-ash had similar interfacial chemistry properties. Also, bulk density, water absorption, and microstructure properties of each pellet was observed that made by silp casting method and manufactured at $50^{\circ}C$ intervals between $1000{\sim}1250^{\circ}C$. As a result, dispersed slip of clay and bottom ash are possible for slip casting and plastic forming process because they exhibit Bingham plastic behavior. Products that made by slip with dispersed clay and bottom ash are not only suitable for KS L 4201 and KS L 1001 at $1250^{\circ}C$ but it is also possible to apply for ceramic and sanitary ware because specific gravity was about 15 % lighter than general ceramic materials.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.511-519
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• 2015

Methods such table flow, slump and outflow time have used to be as a main evaluation criteria regards to fluidity of concrete. Since those methods mentioned above have some inaccuracies which are up to its condition of test. Studies that evaluate fluidity applying the rheology has increased its portion in this field. Meanwhile, demands for AAS binder have been increased in accordance with its demand for this market, studies for rheology of AAS binder are little though. Therefore, this paper mainly deals a rheological peculiarity of AAS binder according to its condition of W/B ratio and alkali activators. The fluidity of AAS paste was evaluated with the index of table flow and outflow time. And shear stress following its shear rate was analyzed through rheological test. Rheological parameters were deduced through this rheological test of Bingham model and analyzed its interrelation with fluidity test. As the final outcome, it proposed the interrelation among table flow, yield stress, viscosity and outflow time. In basis of this study, we would like to suggest a reference for mixing AAS mortars and concretes.

• Korean Journal of Food Science and Technology
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• v.31 no.1
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• pp.24-29
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• 1999

The physicochemical properties of tagatose, a low calorie sweetener, was investigated. Rheological property of tagatose solution was found to be Bingham fluid. As the concentration of tagatose increased from 10 to 50% at $25^{\circ}C$, the viscosity increased from 1.65 to 5.14 cp. When the temperature of 40% tagatose solution increased from 15 to $55^{\circ}C$, the viscosity decreased from 4.59 to 2.33cp. The melting onset temperature and endothermic enthalpy of tagatose were $130.4^{\circ}C$ and -202.3 J/g, respectively, which were obtained from the analysis of differential scanning calorimetry. Tagatose showed higher water absorption than sucrose under $85{\sim}100%$ of relative humidity. Tagatose was less soluble than sucrose at $20{\sim}70^{\circ}C$. Water activity of tagatose in 60% concentration was 0.892, which was lower than 0.957 of sucrose solution. Tagatose solution adjusted from pH 2 to pH 12 was stable after 3 days. Amount of tagatose was not changed after heat treatment at $154^{\circ}C$ for 4 hours. But a browning reaction was found and absorbance of a tagatose solution increased with heat treatment.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.23-27
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• 2013

The risks of debris flows caused by climate change have increased significantly around the world. Recently, landslide disaster prevention technology is more focused on the failure and post-failure dynamics to mitigate the hazards in flow-prone area. In particular, we should define the soil strength and flow characteristics to estimate the debris flow mobility in the mountainous regions in Korea. To do so, we selected known ancient landslides area: Inje, Pohang and Sangju debris flows. Firstly we measured physical and mechanical properties: liquidity index and undrained shear strength by fall cone penetrometer. From the test results, we found that there is a possible relationship between liquidity index and undrained shear strength, $C_{ur}=(1.2/I_L)^{3.3}$, in the selected areas, even though they were different in geological compositions. Assuming that the yield stress is equal to the undrained shear strength at the initiation of sliding, we examined the flow characteristics of weathered soils in Korea. When liquidity index is given as 1, 1.5 and 3.0, the debris flow motion of weathered soils is compared with that of mud-rich sediments, which are known as low-activity clays. At $I_L=1$, it seems that debris flow could reach approximately 250m after 5 minutes. As liquidity index increased from 1 to 3, the debris flow propagation of weathered soils is twice than that of low-activity clays. It may be due to the fact that soil masses mixed with the ambient water and then highly fragmented during flow, thereby leading to the high mobility. The results may help to predict the debris flow propagation and to develop disaster prevention technology at similar geological settings, especially for the weathered soils, in Korea.