현장용 시멘트페이스트 레올로지 측정기구 개발

현철 대한건축학회 2007 大韓建築學會論文集 : 構造系 Vol.23 No.6

Rheological tests on cement paste were necessary for evaluation of workability on field. The slump, mini cone, and marsh cone test are common methods for assessing the flow properties of fresh cement paste and concrete. Although these methods provide quantitative measures of workability, the relationship between these methods and more quantitative rheological parameters is not fully understood. Some appliances for more accurate measurement are recently proposed. However, these are too expensive to use in field. Therefore, the goal is to propose the simple, cheap and useful rheometer for measuring the rheological properties of cement paste and concrete. In this study, C-P Rheometer consisting of a cylinder and a pipe is proposed. Yield stress of cement paste is calculated by measuring the height of cement paste in cylinder when it finishes dropping. Plastic viscosity is also done by measuring the time for cement paste to drop and pass through the range between two fixed heights of cylinder. The new rheometer is in excellent agreement with the experimental yield stress and plastic viscosity data obtained using the authorized rheometer(Brookfield RVDVⅢ+). The conclusion is that this new simple rheometer is reliable for measuring the rheological properties of cement paste.

그릇에 관한 명상 - 이지엽

현철 고요아침 2014 시조시학 Vol.51 No.-

고속 발사 자율 수중 운동체의 초기 불안정 구간 제어 기법 설계 및 검증

현철 제어로봇시스템학회 2023 제어로봇시스템학회 국내학술대회 논문집 Vol.2023 No.6

적외선 윈도우용 가스식 냉각장치 해석 기법

현철봉,구남서,김재영,이호성,Hyun, Cheol-Bong,Goo, Nam-Seo,Kim, Jae-Young,Lee, Ho-Sung 한국군사과학기술학회 2012 한국군사과학기술학회지 Vol.15 No.2

In this paper, a post-analysis of cooling system for infrared(IR) window was performed based on heating experiment of IR window system. We applied the same experimental conditions to analysis, and then validated the analysis technique by comparing numerical and experimental results. For an analysis software, we used a professional heat/fluid analysis program and the numerical and experimental results were in fairly good agreement. We investigated the effect of thermal transfer between the frame and IR window and also a cooling efficiency between fluid and structure in order to determine the proper parameters for the analysis. In this study, 100 % thermal transfer between the frame and IR window and 30 % cooling efficiency between fluid and structure have been proposed, which can be used in the future conceptual design and analysis of similar IR windows.

자율 수중 운동체에 대한 비연성 제어기 설계 및 시뮬레이션을 통한 성능 평가

현철,이동준 제어로봇시스템학회 2012 제어로봇시스템학회 국내학술대회 논문집 Vol.2012 No.4

순환잔골재를 사용한 모르터의 물성에 관한 연구

현철 경성대학교 공학기술연구소 2010 공학기술연구지 Vol.16 No.-

Lately, Korea government recommends that concrete maker use more recycled sand in concrete production. Recycled sand needs consuming way because waste concrete cause environmental problems in case of burying in the ground. But the influence of recycled sand about concrete properties including strength and workability is not perfectly researched. Therefore, it is very necessary for recycled sand to be studied about cocrete properties. The aim of this study is to investigate the influence of recycled sand on the properties of mortars that included three different recycled sands. The properties of the mortars were tested with four kinds of sands including three recycled sands and natural sand. The mortars were prepared with the same content. A reference mix was prepared with 100% natural sand, and it was gradually replaced by each recycled sand. The compressive strength of mortars with mixed sands decreased as recycled sand replaced natural sand. In this paper the parameters of Bingham model about cement mortar with recycled were also investigated. According to mix ratio with three recycled sands, the rheological properties of cement mortar were changed. However, slump test or flow test do not allow to obtain information concerning more fundamental phenomena. Rheology has also been used to study the mechanical properties of cement mortar from mixing up to setting. Superplasticiser (SP) was not used. A general mixer was used to study rheology during the very first minutes following the end of mixing. This study evaluated the effect of water/cement ratio (W/C), types of recycled sands and replacement ratio of recycled sand in mortar. The rheometer was used for testing the behaviour of cement mortar.

반구형 공진 자이로스코프를 위한 디지털 재평형 제어기 설계

현철,강태삼 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.4

본 논문에서는 H∞ 제어 기법을 이용하여 반구형 공진 자이로스코프(HRG)를 위한 재평형 제어기를 설계하였다. HRG 는 진동형 자이로스코프 중에서 가장 정밀한 성능을 갖는 센서로서, 보통 수 kHz 의 공진 주파수 대역에서 동작한다. HRG 의 전기적인 신호는 공진 주파수에 변조된 형태를 갖기 때문에, 저주파 대역에서 주로 적용되는 일반적인 제어 기법은 적용할 수 없다. 본 논문에서는 H∞ 제어 기법을 이용하여 HRG 의 특성에 적합한 제어기를 설계하고 평가하였다. 그리고 설계된 제어기를 디지털 신호처리(DSP) 보드를 이용하여 구현하고, 실제 HRG 샘플에 대한 실험을 수행함으로써 이를 검증하였다. In this paper, H∞ rebalance controller for hemispherical resonator gyroscope is designed. Hemispherical resonator gyroscope(HRG) is one of the coriolis vibratory gyroscope(CVG) which has very stable quartz hemispherical resonator and shows very precise performance. HRG signals are usually modulated at the several kHz of resonant frequency. So the general control scheme cannot be applied directly because general control schemes mainly focused at low frequency range. In this paper, H∞ controller which is suitable for HRG properties is designed. The H∞ controller for HRG is robust to model uncertainties and has advantages in ease of implementation and analysis. From the experiments, it is verified that the proposed control loop is successfully operated.

시멘트페이스트의 細孔構造예측에 관한 연구

현철 慶星大學校 1998 論文集 Vol.19 No.2

In this paper, we propose an analytical model to represent the hysteresis behavior of pore production in cement paste. The proposed model is based upon the physical phenomenon of ion diffusion in cement paste and chemical phenomenon of hydration in cement particle. The proposed model can predict the hydration ratio, the pore volume ratio and the pore structure in cement paste under variable environmental conditions satisfactorily.

측두엽 간질로 인정된 환자들의 MRI와 EEG에 대한 ICTAL SPECT의 Sensitivity와 Specificity

현철호 ( Chul Ho Hyun ),김병수 ( Byung Su Kim ) 대한임상검사과학회 1998 대한임상검사과학회지(KJCLS) Vol.30 No.2

The efficacy of MRI, CCTV -EEG monitoring and ictal SPECT for the localization of seizure foci was evaluated in 21 patients with temporal lobe epilepsy. Ictal and interictal Tc-99m-Ethyl Cysteinnate Dimer(ECD) cerebral perfusion SPECT images of 21 patients were processed to get parametric subtracted images. Epileptogenic foci of 17 patients among 18patients were diagnosed by seizure free state after resection of epileptogenic zones. we found epileptogenic zones in substraction SPECT and compared with visual diagnosis of ictal and interictal MRI, CCTV -EEG monitoring and SPECT. The sensitivity was 100%, the specificity was 14 of 15(93%) in CCTV -EEG monitoring and ictal SPECT. The sensitivity was 100%. the specificity was 14 of 15(94%) in MRI and ictal SPECT.

구조용골재로서 적용가능한 구형(球形)셸경량골재의 개발연구

현철 대한건축학회 2007 大韓建築學會論文集 : 構造系 Vol.23 No.6

In this study, the spherical shell lightweight aggregate is developed as a structural aggregate, which is made by using half spherical mold and ball shaped press. The shell structure is very beneficial in case of construction for huge space. The purpose of this study is to suggest the way how to make the spherical shell lightweight aggregate and evaluate its feasibility as a structural aggregate. The mass production of the spherical shell lightweight aggregate seems possible because the method to make it is relatively simple and its material is general clay. The quality control of the spherical shell lightweight aggregate is also easy due to using mold and ball shaped press. It is possible to make the spherical shell lightweight aggregate with various diameter and surface thickness by changing the diameters of half spherical mold and ball shaped press. This study is about only one type of spherical shell lightweight aggregate.Conclusion obtained are summarized as follows :1) The density of lightweight aggregate is 1.40 g/cm3.2) The water absorption of lightweight aggregate is 2.23%3) The compressive strength of lightweight concrete is ranged from 27.4 MPa to 30.2 MPa. 4) The unit weight of lightweight concrete is ranged from 1.87 t/m3 to 1.96 t/m3.