흙을 혼화재로서 이용한 콘크리트의 개발

현철 경성대학교 환경문제연구소 2000 環境硏報 Vol.10 No.1

Soil is ecological and healthful material. Specially loess among soil is more effective. The producing places of loess are common under the mountain surface. The purpose of this study is to investigate development of concrete adding soil as admixture. This study shows characteristics of compressive strength, fluidity, autogenous shrinkage and abaibatic temperature rise according to the replacement ratios of loess powder and W/C ratio through experiment. In this study, It is reported that the concrete of mixing ratio 5% of loess is most effective. The results obtained are as follows, 1)In case of normal temperature curing and mixing ratio 5% of loess, the compressive strength of concrete is similar to the case without loess. Generally, compressive strength of concrete decrease according to increase of mixing ratio of loess. 2)In case of normal temperature curing and mixing ratio 5% of loess, the fluidity of concrete is nearly equal to the case without loess. Generally, fluidity of concrete decrease according to increase of mixing ratio of loess. 3)In case of W/C ratio 40% and mixing ratio 5% of loess, the autogenous shrinkage of concrete is similar to the case without loess. But in case of W/C ratio 35%, autogenous shrinkage of concrete grow according to increase of mixing ratio of loess. 4)It is proved that abaibatic temperature rise of concrete considerably decrease with increase of mixing ratio of loess.

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

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

미지 우주물체 궤도 정보 획득을 위한 스트릭 추정 방법 검토

현철,이상욱,이호진,이종민 한국정보통신학회 2018 한국정보통신학회논문지 Vol.22 No.11

In an optical observing system, three pairs of observations at equal time intervals are required for the orbitdetermination method to obtain orbital information of an unknown space objects. In this paper, we propose a method ofestimating a streak for acquiring three pairs of observations using one streak image information. Satellite trajectorysimulation data were generated for nine cases using the STK program in order to verify the characteristics of the orbitof space object and estimation performance. Simulation was performed by applying three approaches that can estimate thenext streak position after a few seconds from one streak image information, and the estimation performance wasevaluated. Linear vector method and Kalman Filter method based on the linear assumption tend to increase the estimationerror in the region where the nonlinearity is large. However estimation method using the polynomial curve fitting basedon the least square method showed smaller and uniform error result than the previous methods. 광학관측 시스템에서, 미지의 우주물체의 궤도 정보를 얻을 수 있는 궤도 결정 방법에는, 균등한 시간 간격의 세쌍의 관측 값이 필요하다. 본 논문에서는 하나의 스트릭 영상의 정보를 이용하여, 세 쌍의 관측 값을 획득하기 위한스트릭 추정 방법에 대하여 살펴본다. 우주 물체의 궤도에 따른 특성을 확인하고, 추정 성능을 평가하기 위하여, STK프로그램을 이용하여 총 9가지 경우에 대한 위성 궤적 모의 관측 자료를 생성하였다. 하나의 스트릭 영상 정보로부터수 초 후의 다음 스트릭 위치를 추정할 수 있는 세 가지 접근 방법을 적용하여 시뮬레이션을 수행하고, 추정 성능을평가해 보았다. 선형 가정을 기본으로 하는 선형 벡터 방법과 Kalman Filter 방법은 비선형성이 커지는 부분에서 추정 오차도 함께 증가하는 경향을 보였으나, 최소자승 기법을 기반으로 한 다항식 커브 피팅을 통한 추정 방법은, 앞선방법들 보다 오차 값이 작고 균일한 결과를 보였다.

광학 우주 관측 시스템의 미지 우주물체 위치 추적 분석

현철,이상욱,이호진,박승욱,Hyun, Chul,Lee, Sangwook,Lee, Hojin,Park, Seung-Wook 한국정보통신학회 2021 한국정보통신학회논문지 Vol.25 No.12

In this paper, we check the possibility of continuous tracking when photographing unknown space objects in a short period of time in an optical observation system on the ground. Simulated observation data were generated for target limited to low-orbit areas. The performance index of the prediction error was set in consideration of the property of targets. Kalman Filter was applied to predict the next location of the target. A constant velocity/acceleration dynamic model was applied to the two axes of the azimuth/elevation of the unknown space object respectively. As a result of performing the Monte Carlo simulation, the maximum error ratio of the maximum nonlinear section was less than 2%, which could be determined to ensure continuous tracking. The CA model had little change in the prediction error value for each case, making it more suitable for tracking unknown space objects. This analysis could provide a foundation for determining the orbit of unknown space objects using optical observation. 본 논문에서는 지상의 광학 관측 시스템에서 미지 우주물체를 짧은 주기로 촬영할 때의 연속 추적 가능성을 확인해 본다. 저궤도영역으로 한정된 대상 표적에 대해 모의 관측 데이터를 생성하였고, 표적특성을 고려하여 예측 오차의 성능지수를 설정하였다. 칼만 필터를 이용하여 표적의 다음 위치를 예측하였고, 등속도/등가속도 표적 기동 모델이 미지 우주물체의 방위각/고도각 두 축에 적용되었다. 몬테카를로 시뮬레이션을 수행한 결과, 최대 비선형구간의 최대 오차 비율이 2% 미만으로 나타나 연속적인 추적을 보장할 수 있다고 판단할 수 있었다. 등가속도 모델이 케이스별 예측 오차값의 변화가 적어서, 미지 우주물체의 추적에 더 적합하였다. 이러한 분석은 광학 관측을 이용한 미지 우주물체 궤도 결정의 기초를 제공할 수 있다.

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.

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.

모르터의 자기수축예측에 관한 연구

현철 경성대학교 공학기술연구소 2003 공학기술연구지 Vol.S2 No.2

Autogenous shrinkage of concrete has been defined as decrease in volume due to hydration. For ordinary concretes, autogenous shrinkage is so little that it has been dignored. It has recently been reported, however, that cracking can be caused by autogenous shrinkage, when high-strength concretes were used. In this study, we propose an analytical system to represent autogenous shrinkage in cement paste and mortar in order to control crack due to autogenous shrinkage. The system composed of the hydration model and pore structure model. The hydration model which refined Tomosawa's represents the situation that inner and outer products are made in cement paste. The pore structure model is based upon the physical phenomenon of ion diffusion in cement paste. The proposed model can predict the hydration ratio and the cumulative pore volume in cement paste satisfactorily. Autogenous shrinkage was predicted by elastic modulus calculated from experiment data and former study. The model for predicting autogenous shrinkage of cement paste and mortar shows a reasonable agreement with the experimental data in case of different mix-proportions.

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

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

소형 자율 수중 운동체의 비연성 제어기 설계 및 HILS 기법을 이용한 성능 평가

현철,Chul, Hyun 한국군사과학기술학회 2013 한국군사과학기술학회지 Vol.16 No.2

In this paper, decoupled controller design for Autonomous Underwater Vehicle(AUV) and its simulated performance test results and Hardware In the Loop Simulation(HILS) results are presented. Control system design is done using the PD control scheme. Stability analysis and step response of closed loop system under uncertain parameter condition are also presented. The results of full coupled nonlinear model simulation show the well applicability of the designed controller. From the results of HILS, we can verify performance of real time processing and implemented hardware for AUV.

희곡 : <犬>

현철 향토문학연구회 2008 향토문학연구 Vol.11 No.-