• Journal of the Korea Convergence Society
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• v.11 no.11
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• pp.195-201
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• 2020

This paper implemented quadcopter-type drone system and proposed the heuristic method for obtaining the optimum gain coefficients in order to minimize the settling time. Control system for quadcopter posture stabilization reads the posture data from accelerator and gyro sensor, revises the original posture data using Mahony filter, and drives 4 DC motors using PID controller. The first step of the proposed method is to obtain the gain coefficients using the Ziegler-Nichols method, and then determine the optimum gain coefficients using the heuristic method at the next 3 steps. The experimental result shows that the maximum overshoot decreases from 44.3 to 29.8 degrees and the settling time decreases from 2.6 to 1.7 seconds compared to the Ziegler-Nichols method. Therefore, we proved that the proposed method works well in quadcopter flight system with high motor noise while reducing trial and error to obtain the optimal PID gain coefficients.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1054-1064
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• 2009

In this work, we predict a true fracture strain using load-displacement curves from tensile test and finite element analysis (FEA), and suggest a method for acquiring true stress-strain (SS) curves by predicted fracture strain. We first derived the true SS curve up to necking point from load-displacement curve. As the beginning, the posterior necking part of true SS curve is linearly extrapolated with the slope at necking point. The whole SS curve is then adopted for FE simulation of tensile test. The Bridgman factor or suitable plate correction factors are applied to pre and post FEA. In the load-true strain curve from FEA, the true fracture strain is determined as the matching point to test fracture load. The determined true strain is validated by comparing with test fracture strain. Finally, we complete the true SS curve by combining the prior necking part and linear part, the latter of which connects necking and predicted fracture points.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.51-61
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• 2000

This paper discusses the homogenization method to determine effective average elastic constants of a linear structure by considering its microstructure. A detailed description on the homogenization method is given for the linear elastic material and then the finite element approximation is performed for an investigation of elastic properties. An asymptotic expansion is carried out in the cross-section area, or in the unit cell. Two and three lay-up structures made up of individual isotropic constituents are chosen for numerical examples to check discrepancies between results generated by this theoretical development and the conventional approach. Asymptotic characteristics of the process in extracting the stiffness of structure locally formed by spatial repetitions yield underestimated values of stiffness. These discrepancies are detected by the asymptotic corrective term which is ascribed to considerations of microscopic perturbations and proved in the finite element formulation. The asymptotic analysis is the more reasonable in analysing the composite material, rather than the conventional approach to calculate the macroscopic average for elastic properties.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.187-192
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• 1998

Generally the solidified microstructures of materials consist of the columnar and equiaxed dendritic regions, and many theoretical studies about columnar-to-equiaxed transition have been done because that is closely related to the mechanical and physical properties of products. In this study, the modified equation based on the Hunt's analytical columnar-to-equiaxed transition condition which was derived from heterogeneous nucleation and grain growth in front of the columnar dendrite tip under directional solidification, was obtained applying the growth-velocity-dependent distribution coefficient and liquidus slope to Hunt's. The effects of the number of nucleation sites, nucleation temperature, alloy composition, growth velocity and liquid temperature gradient on the transition for Al-Cu alloys have been investigated.

• Journal of the Korean Data and Information Science Society
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• v.24 no.2
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• pp.267-275
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• 2013

Among data mining techniques, the association rule is the most recently developed technique, and it finds the relevance between two items in a large database. And it is directly applied in the field because it clearly quantifies the relationship between two or more items. When we determine whether an association rule is meaningful, we utilize interestingness measures such as support, confidence, and lift. Interestingness measures are meaningful in that it shows the causes for pruning uninteresting rules statistically or logically. But the criteria of these measures are chosen by experiences, and the number of useful rules is hard to estimate. If too many rules are generated, we cannot effectively extract the useful rules.In this paper, we designed a variety of non-linear regression equations considering all association thresholds between the number of rules and three interestingness measures. And then we diagnosed multi-collinearity and autocorrelation problems, and used analysis of variance results and adjusted coefficients of determination for the best model through numerical experiments.

• Journal of Korean Society of Transportation
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• v.22 no.7 s.78
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• pp.17-23
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• 2004

교통정책을 평가하기 위해 기본적으로 요구되는 Data 중 가장 근본이 되는 것이 OD이다. 기존의 교통정책을 평가함에 있어서 일반적으로 사용되고 있는 OD는 AADT(Annual Average Daily Traffic) OD이다. 계절별 평일/주말 교통량의 분산이 매우 크다는 것은 기존 조사나 연구로 익히 알려진 사실이며, 또한 사회 경제적인 여건의 변화 및 주 5일제 근무제의 시행 등으로 여가통행의 비중이 높아짐에 따라 평일과 주말의 교통량의 분산은 더욱 커질 것으로 예상된다. 따라서 교통정책을 평가하는 방법도 AADT OD의 일률적인 적용이 아닌 교통량의 계절별 평일/주말의 분산을 적용시킨 OD를 가지고 교통정책을 평가하는 방법이 교통정책을 결정함에 있어 오류를 범할 가능성을 적게 될 것으로 예상된다. 기존 연구에서는 이러한 교통량의 분산의 보정을 지점교통량에 한정하여 보정하고 있어 실질적인 네트워크 분석에 적용하기에는 무리가 있다. 이에 본 연구에서는 관측된 TCS Data를 이용하여 계절별 평일/주말의 OD 교통 패턴을 분석하여 계절별 평일/주말의 OD 교통패턴을 반영할 수 있는 보정계수를 산출하고 산출된 보정계수에 따라 AADT OD를 보정하여 네트워크 분석의 기초 자료를 구축하였다. 수정된 OD 교통량의 검증을 위하여 기존의 AADT OD의 인구당 통행발생비율과 계절별 평일/주말 OD의 통행발생량을 비교하였다. 그 결과 소수점 두 자리수에서 오차가 발생하여 비교적 합리적인 OD가 추정되었다. 또한 기존의 AADT OD를 이용하여 정책 결정을 할 때의 오류 가능성을 보이기 위하여 각 계절별 평일/주말 OD 교통량과 기존의 AADT OD를 입력 자료로 각각의 네트워크 분석 후 총통행시간의 차이를 분석하였다. 그 결과 정책 결정에 영향을 미칠 수 있을 정도의 차이가 있는 것으로 분석되었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.250-254
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• 2005

국내의 상수원수 확보는 대부분을 표류수에 의존하고 있으나, 표류수의 경우 수질오염의 증가와 돌발 수질 오염 사고에 대한 대응 등의 취약점을 가지고 있다. 이러한 문제점을 해결하기 위해 근본적으로 깨끗한 상수원수를 확보하기 다양한 방법이 모색되어지고 있다. 수량적으로 안정적이고, 수질적으로 안전한 상수원수 취득 방법으로 강변여과수, 지하댐, 인공함양기법 등이 실질적으로 계획되어 시행되어지고 있다. 특히 강변 충적층의 자연정화 기능을 이용한 강변여과수 개발은 지하수 개발과 달리 수량적으로 안정적이고, 수질적으로 안전한 강변여과수 개발 방안이 적극적으로 진행되고 있다. 낙동강 하류 지역인 함안군, 창원시, 김해시 등은 대부분 하천 표류수에 의존하였으나, 유역내 충적층 발달 지역이 분포해 있고, 하상경사, 하상계수 등의 하천공학적 측면에서 강변여과수 개발에 유리한 입지조건을 가지고 있어 강변여과수 개발이 진행되고 있다. 현재 창원시 대산면 일대에서 국내최초로 방사형집수정을 이용한 강변여과수 개발이 진행되고 있으며, 현재 방사형 취수정 1기가 시공 완료되어 시험 가동 중에 있다. 본 연구에서는 창원시 대산면 일대에서 진행되고 있는 방사형 집수정 설치에 따른 양수시험을 실시하여 양수량에 따른 수위하강 겋항 등을 분석하여 적정 산출량을 결정하였고, 계획단계에서 적정 산출량 예상시 사용한 경험식(Petrovic, Milojevic 경험식)의 적합성 여부에 중점을 두어 진행 되었다. 연구대상 지역인 창원시 대산면 일대는 지하수위가 하천수위보다 높은 이득하천의 형태로 건기시 하천특성을 뚜렷하며, 양수실험을 위한 대용량 양수펌프 설치, 유량검증을 위한 대형 웨어 설치, 수위변화 측정을 위한 디지털 수위계 등을 설치하여 실험을 수행하였다. 단계/장기양수시험을 통하여 양수량-수위하강 경향을 분석하여 방사형 집수정 1기의 적정 양수량은 약 $16,000m^3/day$로 예상하였으며, 계획 시 사용한 경험식(Milojevic)으로 산정된 산출예상량과 유사한 특성을 나타내었다.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.1
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• pp.7-14
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• 1999

The purpose of this study is to evaluate the relationship between ocular components and refractive error for human eye. Ocular components were measured by keratometry, phakometry, and ultrasonography. Refractive error was measured by subjective refraction on 38 subjects aged from 17 to 30. The results were as follows; 1) Refractive error and axial length, vitreous chamber depth, axial length/corneal radius were highly correlated that the correlation coefficients were 0.95, 0.96, 0.95, respectively. 2) Refractive error and corneal radius, corneal power, lens thickness were correlated with the correlation coefficients for 0.60, 0.66, 0.67 respectively. 3) There were no significant correlation between refractive error and corneal thickness.

• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.1
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• pp.68-77
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• 1998

The purpose of this paper is to establish a method estimating the daily urban water demand using statistical analysis that is used for developing the efficient management and operation of the water supply facilities, and accurary of the model is verified by error rate and F-value. The data used in this study were the daily urban water use, the weather conditions such as temperature, precipitation, relative humidity, etc, and the day of The week. The case study was taken placed for the city of Namwon in Korea. The raw data used in this study were rearranged either by month or by season for analysis purpose, and the statistical analysis was applied to the data to obtain the regression model As a result of this study, the linear regression model was developed to estimate the daily urban water use with weather condition. The regression constant and coefficients of the model were determined for each month of a year. The accuracy of the model was within 3% of average error and within 11% of maximum error. The resulting model was found to he useful to the practical operation and management of the water supply facilities.

• Tunnel and Underground Space
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• v.20 no.3
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• pp.225-232
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• 2010

In this study, a newly modified 3-dimensional strain-dependent hydraulic conductivity modification relation which incorporates the influences of normal deformation and shear dilation is suggested. Since rock mass is simulated as a orthogonally jointed medium, an anisotropic hydraulic conductivity field can be evaluated using that relation. The empirical relationship on the basis of GSI and disturbance factor has been used to estimate the value of a modulus reduction ratio (ratio of rock mass deformation modulus to rock matrix elastic modulus). Principal hydraulic conductivity directions is not generally coincident with the global coordinate due to the inclining of joint and the influence of joint inclination is evaluated under strain rotation. Result shows that change of hydraulic conductivity does decreases with the increase of GSI and disturbance factor has much effects on the hydraulic conductivity of rock mass getting GSI value above 50. It is found that the inclination of joint impacts on the variation of hydraulic conductivity.