• 제어로봇시스템학회논문지
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• 제2권4호
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• pp.306-311
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• 1996

This paper discusses the maintenance of the water level of steam generators at its programmed value. The process, the water level of a steam generator, has the nonminimum phase property. So, it causes a reverse dynamics called a swell and shrink phenomenon. This phenomenon is severe in a low power condition below 15 %, in turn makes the start-up of the power plant too difficult. The control algorithm used here incorporates a pole-assignment scheme into the minimum variance strategy and we use a parallel adaptation algorithm for the parameter estimation, which is robust to noises. As a result, the total control system can keep the water level constant during full power by locating closed-loop poles appropriately, although the process has the characteristics of high complexity and nonlinearity. Also, the extra perturbation signals are added to the input signal such that the control system guarantee persistently exciting. In order to confirm the control performance of a proposed pole-assignment self-tuning controller we perform a computer simulation in full power range.

• Wind and Structures
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• 제18권5호
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• pp.567-598
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• 2014

In this paper, wind induced aerodynamic loads on a standard tall building have been evaluated through large-eddy simulation (LES) technique. The flow parameters of an open terrain were recorded from the downstream of an empty boundary layer wind tunnel (BLWT) and used to prescribe the transient inlet boundary of the LES simulations. Three different numerically generated inflow boundary conditions have been investigated to assess their suitability for LES. A high frequency pressure integration (HFPI) approach has been employed to obtain the wind load. A total of 280 pressure monitoring points have been systematically distributed on the surfaces of the LES model building. Similar BLWT experiments were also done to validate the numerical results. In addition, the effects of adjacent buildings were studied. Among the three wind field generation methods (synthetic, Simirnov's, and Lund's recycling method), LES with perturbation from the synthetic random flow approach showed better agreement with the BLWT data. In general, LES predicted peak wind loads comparable with the BLWT data, with a maximum difference of 15% and an average difference of 5%, for an isolated building case and however higher estimation errors were observed for cases where adjacent buildings were placed in the vicinity of the study building.

• 대한기계학회논문집
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• 제12권4호
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• pp.694-704
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• 1988

본 연구에서는 현장에서 흔히 수행되는 가공 후(post-process) 측정만을 이용 한 단일절삭(single-pass)으로써 공작물이 원하는 일정한 직경을 유지할 수 있다는 것 을 실험을 통해 검증해 보이고자 한다. 이와 같은 방식은 이미 보오링 작업 중 보오 링바의 노출 길이 변화에 따른 가공면의 내경 오차를 없애주기 위한 방법으로써 제시 된 바 있다. 즉 반복 최소 자승법(recursive least squares)으로 미리 가정된 절삭 조건과 공작물 처짐 사이의 관계식과 관련된 계수를 가공 후에 가공 공작물의 표면 측 정으로 매 번보정(update)시켜 줌으로써 일정 직경을 얻기위한 절삭조건을 결정하고자 한다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.291-300
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• 1998

This paper demonstrates how ambient vibration measurements at a limited number of locations can be effectively utilized to estimate parameters of a finite element model of a large-scale structural system involving a large number of elements. System identification using ambient vibration measurements presents a challenge requiring the use of special identification techniques, which ran deal with very small magnitudes of ambient vibration contaminated by noise without the knowledge of input farces. In the present study, the modal parameters such as natural frequencies, damping ratios, and mode shapes of the structural system were estimated by means of appropriate system identification techniques including the random decrement method. Moreover, estimation of parameters such as the stiffness matrix of the finite element model from the system response measured by a limited number of sensors is another challenge. In this study, the system stiffness matrix was estimated by using the quadratic optimization involving the computed and measured modal strain energy of the system, with the aid of a sensitivity relationship between each element stiffness and the modal parameters established by the second order inverse modal perturbation theory. The finite element models thus identified represent the actual structural system very well, as their calculated dynamic characteristics satisfactorily matched the observed ones from the ambient vibration test performed on a large-scale structural system subjected primarily to ambient wind excitations. The dynamic models identified by this study will be used for design of an active mass damper system to be installed on this structure fer suppressing its wind vibration.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2022년도 학술발표회
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• pp.442-442
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• 2022

고해상도 시공간적 격자 형태의 레이더 강수는 돌발홍수(flash flood)와 같은 기상재해에 대비하기 위하여 실시간 예측정보로 활용된다. 그러나 대부분의 레이더 강수는 과소 추정되는 경향이 있어 정량적인 보정 과정인 QPE (Quantitative Precipitation Estimation)가 필요하다. 일반적으로 레이더 강수자료 보정은 지점 관측자료를 활용하지만, 본 연구에서는 지상 강수량 기반의 고해상도 격자 강수자료를 생산하여 레이더 강수자료와 직접적으로 비교하고자 한다. 이에 고도와 지형적 특성을 고려한 PRISM(Precipitation-elevation Regressions on Independent Slopes Model) 방법을 사용하여 고해상도 격자기반의 자료를 생성하였다. PRISM 방법은 고도와 지리정보를 독립변수로 갖는 회귀모형 기반의 기후인자 추정 모형이다. 생산된 고해상도 격자 강수자료와 레이더 강수자료를 QPF (Quantitative Precipitation Forecast) 모델의 입력자료로 사용하여 예측결과를 비교하였다. 해당 QPF 모델은 이류(advection)와 확률론적 섭동(stochastic perturbation)을 기반으로 하며, 강수 앙상블 자료를 생산한다. QPF 모델에 대해 투 트랙(two-track) 방법으로 생산된 예측정보를 통해 레이더 강수자료의 격자별 후처리 보정이 가능할 것으로 판단된다.

• The Journal of Korean Physical Therapy
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• 제24권5호
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• pp.334-339
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• 2012

Purpose: This study was conducted in order to compare the ability to control postural sway during perturbation when stroke patients received postural sway induced by head rotation. Methods: This study included 15 stroke patients and 15 healthy adults. Each group was measured by 3D motion analysis for determination of the angle of the neck in static position and by balance performance monitor for estimation of swaying angle in both neutral posture and head rotation position. These results were then analyzed in order to compare the healthy control group and the stroke patients group. Results: In both static posture ($60.7{\pm}4.81$) and dynamic posture ($51.46{\pm}6.87$, $70.8{\pm}6.55$), significant decreases were observed in the angle of head rotation of the patient group, compared to the healthy group (p<0.05), and significant decreases were observed in the sway angle of the patient group when in the neutral position ($3.62{\pm}7$, $24{\pm}0.60$) and head rotation ($3.04{\pm}0.80$, $51.46{\pm}6.87$), compared to the healthy group (p<0.05). Conclusion: According to these findings, patients with stroke tend to restrict the ROM of head rotation and swaying angle in dynamic posture and maintain their posture instability using limitation of head movement relative to the trunk and sway angle of area which is larger than that of affected side in unaffected side.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.34.4-35
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• 2008

The significant I&T process gain represented by reduction in overall budget expenditure can be obtained from the use of efficient alignment technique for large space optical systems. Such process gain tends to increase rapidly with an increase in aperture and/or in number of optical elements within the system. However, in practice, the alignment of multiple optical components tends to be rather difficult task because of the multiple coupling effects among the elements within the target system. In order to understand and hence identify the complex interplay of the wavefront coupling effects from the alignment process, the original differential wavefront sampling(DWS) method was presented elsewhere in recent years. DWS uses partial differential of the wavefront of optical component and perturbation value of the optical component against a particular alignment factor. The straightforward application of DWS for an off-axis optical system revealed that it tends to give incorrect estimation of the given misalignment state. In this study, we added off-axis correction terms to the original DWS algorithm and investigated its alignment performance. The performance simulation result for a Korsch type space optical system shows that the modified DWS is capable of bringing the misaligned system into the target alignment tolerance only after 3 iterations. It also shows that this new improved algorithm can be used to estimate the source misalignment as well. We are planning to apply this method for the alignment of a 800mm Korsch type telescope in the near future. We discuss the computational technique, simulation results and implications in details.

• 한국추진공학회지
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• 제23권6호
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• pp.1-10
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• 2019

노즐 내 파동은 노즐목을 빠져나가는 유동의 공력음향학적인 효과로 인해 연소불안정을 감쇠시키는 주요 요소 중 하나로 알려져 있다. 이와 같은 효과는 노즐 어드미턴스라는 지표를 통해 정량적으로 평가가 가능하다. 본 연구에서는 현재까지 로켓 연소불안정 억제에 가장 효과적인 노즐감쇠(nozzle damping)와 연계된 노즐 어드미턴스를 구하는 여러 기법을 소개한다. 이중, 가장 널리 알려진 1차원 선형 오일러 방정식을 도입하여 노즐의 주 설계 변수에 따른 노즐 어드미턴스의 경향을 분석하였다. 분석 결과, 노즐 수축부 길이가 짧아질수록 축방향 노즐 어드미턴스의 값이 낮게 나타나는 주파수 영역대가 확장되므로 짧은 노즐일수록 주파수 의존성을 줄인다는 기존 이론을 검증하였다. 또한, 짧은 노즐 이론을 통한 어드미턴스 예측은 1차 접선방향 압력 섭동에는 적합하지 않음을 알 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제32권3호
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• pp.237-245
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• 2015

A strategy is needed for a regional survey of geosynchronous orbits (GSOs) to monitor known space objects and detect uncataloged space objects. On the basis of the Inter-Agency Debris Committee's recommendation regarding the protected region of geosynchronous Earth orbit (GEO), target satellites with perigee and apogee of $GEO{\pm}200km$ and various inclinations are selected for analysis. The status of the GSO region was analyzed using the satellite distribution based on the orbital characteristics in publicly available two-line element data. Natural perturbation effects cause inactive satellites to drift to two stable longitudinal points. Active satellites usually maintain the designed positions as a result of regular or irregular maneuver operations against their natural drift. To analyze the detection rate of a single optical telescope, 152 out of 412 active satellites and 135 out of 288 inactive satellites in the GSO region were selected on the basis of their visibility at the observation site in Daejeon, Korea. By using various vertical view ranges and various numbers of observations of the GSO region, the detection efficiencies were analyzed for a single night, and the numbers of follow-up observations were determined. The orbital estimation accuracies were also checked using the arc length and number of observed data points to maintain the GSO satellite catalog.

• 한국전자통신학회논문지
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• 제7권6호
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• pp.1413-1422
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• 2012

비선형 적응백스텝핑 제어기법은 외부 환경에 의한 여러가지 파라미터의 변동에도 불구하고 강인한 특성을 가진다. 이를 사용하여 IPMSM(Interior Permanent Magnet Synchronous Motor)의 정밀한 속도제어기를 설계하기 위해서는 빠른 제어 주기를 가져야만 한다. 하지만 속도 측정을 위한 엔코더의 분해능의 제약으로 연산주기를 빠르게 가져가지 못하고, 결국 제어기의 성능을 높이지 못하게 된다. 본 논문은 빠르고 정밀한 속도 제어기를 설계하기 위하여 비선형 적응백스텝핑 제어기법을 적용한 센서리스 속도 제어기 설계 방법을 제안한다. 제어기는 EKF(Extended Kalman Filter)를 이용하여 추정된 속도정보를 이용하여 비선형 적응백스텝핑 제어기법을 사용하는 방식으로 IPMSM의 속도 제어를 수행한다. 제안된 제어기의 성능은 PSIM을 이용한 모의 실험을 통하여 검증하였다.