• 한국방재학회 논문집
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• 제10권3호
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• pp.13-20
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• 2010

실물 충돌 실험을 실시하지 않고 하는 안전구조물의 성능 평가는 컴퓨터 해석에 의한 검토가 불가피하다. 그러나 이러한 컴퓨터 시뮬레이션의 정확도를 높이기 위해서는 연성방호구조물의 차량-가드레일시스템-지반의 상호작용을 고려한 특정 입력변수의 올바른 결정이 중요하게 된다. 본 연구에서는 가아드레일로 대표되는 연성방호구조물의 동적 퍼포먼스를 컴퓨터 시뮬레이션으로 측정하되, 시뮬레이션의 정확도를 높이기 위한 방안을 도출하기위하여 구조물 차량의 충돌 해석에 유용성 이 입증된 Barrier VII 프로그램을 이용하여 입력변수에 대한 출력변수의 변화 양상을 분석함으로써 안전성검토에 있어서 중요한 입력변수를 도출하고 정확한 입력변수를 결정하기 위한 방안을 제시하였다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 춘계학술대회
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• pp.75-78
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• 1997

In the accessment of the performance of a magnetic resonance imaging unit, there are many parameters to be measured. Such measured parameters are not often meaning by itself. Namely, it need to be compared with some standard. Since there is no gold standard MRI, only can be compared with a worldly renowned product. In this report, we attempted to compare a few MRI parameters for the accessment of the performance of 1 Tesla MRI unit which is domestically developed. Though we did not measure all the parameters related to hardware aspects and software aspects for the full comparison, there few parameters may elucidate some important aspects of MRI unit.

• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.237-246
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• 2013

It is of great significance to utilize a landing mechanism to explore an asteroid. A landing mechanism named ALISE (Asteroid Landing and In Situ Exploring) for asteroid with soft surface is presented. The landing dynamic in the first turning stage, which represents the landing performance of the landing mechanism, is built by a Lagrange equation. Three key parameters can be found influencing the landing performance: the retro-rocket thrust T, damping element damping $c_1$, and cardan element damping $c_2$. In this paper, the retro-rocket thrust T is solved with considering that the landing mechanism has no overturning in extreme landing conditions. The damping element damping c1 is solved by a simplified dynamic model. After solving the parameters T and $c_1$, the cardan element damping $c_2$ is calculated using the landing dynamic model, which is built by Lagrange equation. The validities of these three key parameters are tested by simulation. The results show a stable landing, when landing with the three estimated parameters T, $c_1$, and $c_2$. Therefore, the landing dynamic model and methods to estimate key parameters are reasonable, and are useful for guiding the design of the landing mechanism.

• 한국전문물리치료학회지
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• 제22권4호
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• pp.27-33
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• 2015

The purpose of this study was to find which spatiotemporal gait parameters gained from stroke patients could be predictive factors for the gait part of Tinetti Performance-Oriented Mobility Assessment (POMA-G). Two hundred forty-six stroke patients were recruited for this study. They participated in two assessments, the POMA-G and computerized spatiotemporal gait analysis. To analyze the relationship between the POMA-G and spatiotemporal parameters, we used Pearson's correlation coefficients. In addition, multiple linear regression analyses (stepwise method) were used to predict the spatiotemporal gait parameters that correlated most with the POMA-G. The results show that the gait velocity (r=.67, p<.01), cadence (r=.66, p<.01), step length of the affected side (r=.49, p<.01), step length of the non-affected side (r=.53, p<.01), swing percentage of the non-affected side (r=.47, p<.01), and single support percentage of the affected side (r=.53, p<.01) as well as the double support percentage of the non-affected side (r=-.42, p<.01) and the step-length asymmetry (r=-.64, p<.01) correlated with POMA-G. The gait velocity, step-length asymmetry, cadence, and single support percentage of the affected side explained 67%, 2%, 2%, and 1% of the variance in the POMA-G, respectively. In conclusion, gait velocity would be the most predictive factor for the POMA-G.

• Journal of Power Electronics
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• 제18권1호
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• pp.92-102
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• 2018

A sliding mode control (SMC) for servo motors based on the differential evolution (DE) algorithm, called DE-SMC, is proposed in this study. The parameters of SMC should be designed exactly to improve the robustness, realize the precision positioning, and reduce the steady-state speed error of the servo drive. The main parameters of SMC are optimized using the DE algorithm according to the speed feedback information of the servo motor. The most significant influence factor of the DE algorithm is optimization iteration. A suitable iteration can be achieved by the tested optimization process profile of the main parameters of SMC. Once the parameters of SMC are optimized under a convergent iteration, the system realizes the given performance indices within the shortest time. The experiment indicates that the robustness of the system is improved, and the dynamic and steady performance achieves the given performance indices under a convergent iteration when motor parameters mismatch and load disturbance is added. Moreover, the suitable iteration effectively mitigates the low-speed crawling phenomenon in the system. The correctness and effectiveness of DE-SMC are verified through the experiment.

• 한국해양공학회지
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• 제36권4호
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• pp.251-269
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• 2022

The process-based XBeach model has numerous empirical parameters because of insufficient understanding of hydrodynamics and sediment transport on the nearshore; hence, it is necessary to calibrate parameters to apply to various study areas and wave conditions. Therefore, the calibration process of parameters is essential for the improvement of model performance. Generally, the trial-and-error method is widely used; however, this method is passive and limited to various and comprehensive parameter ranges. In this study, the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to estimate the optimal range of three parameters (gamma, facua, and gamma2) using morphological field data collected in Maengbang beach during the four typhoons that struck from September to October 2019. The model performance and optimal range of empirical parameters were evaluated using Brier Skill Score (BSS) along with the baseline profiles, sensitivity, and likelihood density analysis of BSS in the GLUE tools. Accordingly, the optimal parameter combinations were derived when facua was less than 0.15 and simulated well the shifting shape, from crescentic sand bar to alongshore uniform sand bars in the surf zone of Maengbang beach after storm impact. However, the erosion and accretion patterns nearby in the surf zone and shoreline remain challenges in the XBeach model.

• 대한기계학회논문집A
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• 제21권9호
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• pp.1462-1469
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• 1997

This study presents a genetic algorithm-based method for optimizing control parameters in fluid power systems. Genetic algorithms are general-purpose optimization methods based on natural evolution and genetics. A genetic algorithm seeks control parameters maximizing a measure that evaluates system performance. Five control gains of the PID-PD cascade controller fr an electrohydraulic speed control system with a variable displacement hydraulic motor are optimized using a genetic algorithm in the experiment. Optimized gains are confirmed by inspecting the fitness distribution which represents system performance in gain spaces. It is shown that optimization of the five gains by manual tuning should be a task of great difficulty and that a genetic algorithm is an efficient scheme giving economy of time and in labor in optimizing control parameters of fluid power systems.

• 한국음향학회지
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• 제18권3호
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• pp.68-72
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• 1999

바이모달 음성인식 시스템에서 어떤 입술파라미터를 선정하느냐 그리고 얼마나 견인하게 추출하는 가에 따라서 인식률에 큰 영향을 미친다. 그래서 본 논문에서는 자동 추출 알고리듬을 이용하여 입술파라미터를 추출하고 안쪽 입술 파라미터가 바깥 입술 파라미터보다 바이모달 음성인식 시스템에 더 많은 영향을 미친다는 것을 보였다. 그리고 손으로 추출한 추출알고리듬과 비교하여 자동 추출알고리듬의 신뢰성을 비교하였다.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.46-59
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• 2002

The main purpose of this study is to investigate the variation of tool electrode edge wear and machining performance outputs, namely, the machining rate (workpiece removal rate), tool wear rate and the relative wear, with the varying machining parameters (pulse time, discharge current and dielectric flushing pressure) in EDM die sinking. The edge wear profiles obtained are modeled by using the circular arcs, exponential and poller functions. The variation of radii of the circular arcs with machining parameters is given. It is observed that the exponential function models the edge wear profiles of the electrodes, very accurately. The variation of exponential model parameters with machining parameters is presented.

• 한국물환경학회지
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• 제28권2호
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• pp.292-299
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• 2012

The objective of this study is to develop a novel method for evaluating forward osmosis (FO) membrane performances using a non-pressurized FO system. Basic membrane performance parameters including water (A) and solute (B) permeability coefficients and unique parameter for FO membrane such as the support layer structural parameter (S) were determined in two FO modes (i.e., active layer faces feed solution (AL-FS) and active layer faces draw solution (AL-DS)). Futhermore, these parameters were compared with those determined in a pressurized reverse osmosis (RO) system. Theoretical water flux was calculated by employing these parameters to a model that accounts for the effects of both internal and external concentration polarization. Water flux from FO experiment was compared to theoretical water fluxes for assessing the reliability of those parameters determined in three different operation modes (i.e., AL-FS FO, AL-DS FO, and RO modes). It is demonstrated that FO membrane performance parameters can be accurately measured in non-pressurized FO mode. Specifically, membrane performance parameters determined in AL-DS FO mode most accurately predict FO water flux. This implies that the evaluation of FO membrane performances should be performed in non-pressurized FO mode, which can prevent membrane compaction and/or defect and more precisely reflect FO operation conditions.