• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국제학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.1-6
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• 1993

This report proposes a novel method of identification of continuous time-delay systems from sampled input-output data. By the aid of a digital pre-filter, an approximated discrete-time estimation model is first derived, in which the system parameters remain in their original form and the time delay need not be an integral multiple of th sampling period. Then an identification method combining the common linear least squares(LS) method or the instrumental variable(IV) method with the genetic algorithm(GA) is proposed. That is, the time-delay is selected by the GA, and the system parameters are estimated by the LS or IV method. Furthermore, the proposed method is extended to the case of multi-input multi-output systems where the time-delays in the individual input channels may differ each other. Simulation resutls show that our method yields consistent estimates even in the presence of high measurement noises.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.340-346
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• 2008

A level-set method is developed for computation of drop motions in various engineering applications. Compared with the volume-of-fluid method based on a non-smooth volume-fraction function, the LS method can calculate an interface curvature more accurately by using a smooth distance function. Also, it is straightforward to implement for two-phase flows in complex geometries unlike the VOF method requiring much more complicated geometric calculations. The LS method is applied to simulation of inkjet process, thin film pattering and droplet collisions.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.340-346
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• 2008

A level-set method is developed for computation of drop motions in various engineering applications. Compared with the volume-of-fluid method based on a non-smooth volume-fraction function, the LS method can calculate an interface curvature more accurately by using a smooth distance function. Also, it is straightforward to implement for two-phase flows in complex geometries unlike the VOF method requiring much more complicated geometric calculations. The LS method is applied to simulation of inkjet process, thin film pattering and droplet collisions.

• 융합신호처리학회 학술대회논문집
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• 한국신호처리시스템학회 2003년도 하계학술대회 논문집
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• pp.268-271
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• 2003

There are several methods for the design of 2D filter. Notable among them is McClellan transform method. This transform allows us to obtain a high order 2D FIR filter through mapping the 1D frequency points of a 1D prototype FIR filter onto 2D frequency contours. We design 2D filter using this transform. Then we notice for mapping deviation of the 2D filter. In this paper, Quadratic programming (QP) method allows us to obtain coefficients of McClellan transform. Then we compare deviation of QP method with least-squares(LS) method. Elliptic filter is used for comparison. The optimal cutoff frequencies of a 1D filter are obtained directly from the QP method. Also several problem of LS method are solved.

• 화약ㆍ발파
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• 제33권4호
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• pp.7-13
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• 2015

최근에 지하공간의 개발과 활용 기술에 대한 수요가 전 세계적으로 급증함에 따라 역학적 안정성과 활용 효율의 측면에서 발파굴착 시 발생하는 손상대 평가는 주요 관심사가 되고 있다. 본 연구에서는 지하공동주변 발파손상대(blast-damaged zone; BDZ)에 대한 폭원모델링을 검증하기 위하여 모멘텀 트랩(momentum trap; MT) 개념을 이용한 일련의 소규모 시험발파를 실시하고, 시험 결과에 따라 LS-DYNA 수치모델의 입력변수들을 수정하였다. 연구 결과, 본 연구에서 제안한 MT 개념을 이용한 모형발파 실험 및 수치모델링 기법은 주어진 조건 하에서 MT의 비산속도를 잘 모사하는 것으로 나타났다.

• ETRI Journal
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• 제46권3호
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• pp.392-403
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• 2024

Even though generalized frequency division multiplexing is an alternative waveform method expected to replace the orthogonal frequency division multiplexing in the future, its implementation must alleviate channel effects. Least-squares (LS), a low-complexity channel estimation technique, could be improved by using the discrete Fourier transform (DFT) without increasing complexity. Unlike the usage of the LS method, the DFT-based method requires the receiver to know the channel impulse response (CIR) length, which is unknown. This study introduces a simple, yet effective, CIR length estimator by utilizing LS estimation. As the cyclic prefix (CP) length is commonly set to be longer than the CIR length, it is possible to search through the first samples if CP is larger than a threshold set using the remaining samples. An adaptive scale is also designed to lower the error probability of the estimation, and a simple signal-to-interference-noise ratio estimation is also proposed by utilizing a sparse preamble to support the use of the scale. A software simulation is used to show the ability of the proposed system to estimate the CIR length. Due to shorter CIR length of rural area, the performance is slightly poorer compared to urban environment. Nevertheless, satisfactory performance is shown for both environments.

• 대한기계학회논문집A
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• 제39권2호
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• pp.203-209
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• 2015

건설기계 산업에서 배기 및 연비 규제를 만족하기 위하여 엔진 시스템이 점차 전자제어화 되고 있으며, 이를 제어하기 위한 EMS(Engine Management System)의 복잡도 또한 증가하고 있다. 본 연구에서는 EMS function 개발 시, 비용 및 개발기간의 단축을 위한 HiLS(Hardware in the Loop Simulation) 시스템을 개발하였다. HiLS 에 내장된 엔진 모델은 크게 Air, Fuel, Torque 및 동력계 모델로 구성되어있고 실시간 엔진 모사를 위하여 Mean value modeling 방법을 적용하였다. 이 연구를 통하여 개발한 HiLS 시스템은 EGR(Exhaust Gas Recirculation) 시스템과 Turbocharger 가 장착된 건설기계용 디젤엔진을 이용하여 정확성을 검증하였고, 테스트 결과 실 엔진 대비 90% 이상의 정확도를 얻었다.

• 설비공학논문집
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• 제27권9호
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• pp.449-454
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• 2015

In this study, the effects of lock operations on the infiltration rates for the two window types sliding and lift sliding (LS) are investigated through experiment and simulation. The airtightness levels of the two window types-with locks both on and off-were measured according to the KS F 2292 Test method of airtightness that is used for windows and doors. The air-flow rates of both window types with the locks on for a pressure differential of 10 Pa are $1.98m^3/(m^2h)$ and $1.68m^3/(m^2h)$, respectively; with the locks off, the air-flow rates of the sliding and LS windows are $2.64m^3/(m^2h)$ and $5.83m^3/(m^2h)$, respectively, whereby the air-flow rates are 33% higher for sliding and 247% higher for LS. The air change per hour (ACH) was calculated using the ventilation-simulation software CONTAM. For the sliding window, the ACH changed from 0.45 to 0.57 when the lock was operated from on to off, representing an increase of 27%. For the LS window, the ACH changed from 0.29 to 0.81, showing an increase of 179%.

• Earthquakes and Structures
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• 제10권1호
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• pp.141-161
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• 2016

In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities is of crucial importance. Traditionally, LS capacities are defined according to design code provisions or using deterministic pushover analysis without considering the inherent randomness of structural parameters. To assess the effects of structural randomness on LS capacities, ten structural parameters that include material strengths and gravity loads are considered as random variables, and a probabilistic pushover method based on a correlation-controlled Latin hypercube sampling technique is used to estimate the uncertainties in LS capacities for four typical reinforced concrete frame buildings. A series of ten LSs are identified from the pushover curves based on the design-code-given thresholds and the available damage-controlled criteria. The obtained LS capacities are further represented by a lognormal model with the median $m_C$ and the dispersion ${\beta}_C$. The results show that structural uncertainties have limited influence on $m_C$ for the LSs other than that near collapse. The commonly used assumption of ${\beta}_C$ between 0.25 and 0.30 overestimates the uncertainties in LS capacities for each individual building, but they are suitable for a building group with moderate damages. A low uncertainty as ${\beta}_C=0.1{\sim}0.15$ is adequate for the LSs associated with slight damages of structures, while a large uncertainty as ${\beta}_C=0.40{\sim}0.45$ is suggested for the LSs near collapse.

• 한국초전도ㆍ저온공학회논문지
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• 제9권4호
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• pp.32-36
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• 2007

We fabricated and tested a novel hybrid superconducting fault current limiter (SFCL) of three-phase $24kV_{rms}/630A_{rms}$ rating. In order to apply conventional resistive SFCLs into electric power systems, the urgent issues to be settled are as follows, such as initial installation price of SFCL, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. The ac loss and high cost of superconductor and cryostat system are main bottlenecks for real application. Furthermore in order to increase voltage and current ratings of SFCL, a lot of superconductor components should be connected in series and parallel which resulted in extreme high cost. In addition, the method to quench all components at the same instant needs very sophisticated skill and careful operation. Due to these problems, the practical applications of SFCL were pending. Therefore, in order to make practical SFCL, the price of SFCL should be lowered and should meet the demand of utilities. We designed novel hybrid SFCL which combines superconductor and conventional electric equipment including vacuum interrupter, power fuse and current limiting reactor. The main purpose of hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of superconductor and high fast switch. Consequently, it was possible to get the satisfactory test results using this method, and further works for field tests are in the process.