• Journal of Aerospace System Engineering
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• v.17 no.1
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• pp.24-32
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• 2023

This paper studied HART II in descending flight using rotorcraft analysis code based on geometrically exact beam (GEB) model. The present GEB model expressed by a mixed variational formulation could capture the geometrically nonlinear behavior of the blade without arbitrary assumptions. In previous results, correlation of airloads with structural moments for HART II was not as good as blade deflections. However, in present results, predictions of airloads and structural loads are fairly correlated with measured data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.4
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• pp.183-190
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• 2018

This paper presents optimization of the main spar of Human-Powered Aircraft (HPA) wing. Mass minimization was attempted, while considering large torsional deformation of the beam. Sequential Quadratic Programming (SQP) method was adopted as a relevant tool to conduct structural optimization algorithm. An inner diameter and ply thicknesses of the main spar were selected as the design variables. The objective function includes factors such as mass minimization, constant tip bending displacement, and constant tip twist of the beam. For estimation of bending and torsional deformation, the geometrically exact beam model, which is appropriate for large deflection, was adopted. Properties of the cross sectional area which the geometrically exact beam model requires were obtained by Variational Asymptotic Beam Sectional Analysis (VABS), which is a cross sectional analysis program. As a result, maintaining tip bending displacement and tip twist within 1.45%, optimal design that accomplished 7.88% of the mass reduction was acquired. By the stress and strain recovery, structural integrity of the optimal design and validity of the present optimization procedure were authenticated.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.270-281
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• 2017

In this paper, a vibratory disturbance to the rotor system generated by gyroscopic precession through helicopter rotor is examined. Also, active vibration reduction method is designed and simulated by designing feedback controller. For this purpose, structural analysis is carried out using EDISON's geometric exact beam program which can analyze the rotor with the cantilever condition. And the aeroelastic analysis is performed by coupling it with the simple aerodynamic model. In order to obtain the real-time structural response, the EDISON program analysis results were modeled by nonlinear equations and the Newton-Raphson method was used for the trim analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.352-356
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• 1997

이 논문에서는 압전 MEMS에 대한 유한요소해석(FEA)응용이 연구되었다. 압전MEMS와 관련한 특수재료 및 기하학적 형상에 대한 몇 가지 두드러진 특징 및 앞으로의 연구가치가 있는 주제도 아울러 다룬다. 압전 능동박막을 이용한 센서 및 액츄에이터를 포함하는 단순구조에 대한 FEA모델링이 제시되었다. ZnO가 압전 재료로 사용되었다. 정적 전기기계적해석이 두 가지 모델에 대해 수행되었다. 압전효과로 발생한 처짐 및 센 서의 출력전압에 대한 FEA 결과는 해석치 혹은 실험측정값과도 우수하게 일치하였다. ANSYS가 P-MEMS의 가상신속시작체계를 위한 우수한 FEA도구임이 본 논문을 통해서 보여졌다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.18 no.4
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• pp.359-367
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• 2000

This paper suggests that coefficients models of the Earth's gravitational potential can be used to calculate height anomalies which are then reduced to the geoid undulation to determine more precise geoid undulation. The potential coefficients and modified coefficients of EGM96 and KODEM33 digital elevation model in and around the Korean peninsula were used for this study. The magnitude of height anomaly computed in this study reached 0.025 m and the mean vaule showed -0.015 m. In this study, geometrical geoid undulation was derived from GPS/Leveling data for evaluating the precisely computed geoid undulation. In comparison with geometric and gravimetric geoid undulations, mean value and standard deviation of the differences showed 0.0114 m and 0.2817 m respectively and it showed the improvement of results.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.16 no.2
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• pp.213-223
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• 1998

This paper deals with the geoid modelling in and around Korean peninsula referred to Bessel ellipsoid. Several useful data were used to compute precise geoidal heights referred to GRS80 by remove and restore technique and FFT technique was used to evaluate Stokes' integral. All grid point elevations extracted from GTOPO 30 and Bessel coordinates of all grid point were computed through coordinates transformation by applying three transformation parameters. Finally, geoidal heights referred to Bessel ellipsoid were calculated by geometric method. As the results of this study, a precise gravimetric geoid model referred to GRS80 (KOGGDM33) and geoid model referred to Bessel ellipsoid(KOBGDM33) in and around Korean peninsula were developed. KOBGDM33 shows the gradual distribution of geoidal heights from -91.8 m in Yongampo to -39.0 m in the straits of Korea.

• The Korean Journal of Rheology
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• v.9 no.1
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• pp.16-26
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• 1997

사출 성형된 제품에서 발생하는 잔류응력은 최종 제춤의 기하학적 정밀도와 기계적 성질 및 열적 성질에 영향을 미친다. 사출성형된 제품의 잔류응력을 예측하기 위해서는 먼 저 열 및 유동장의 해석을 수행하여야 하고이를 위해서는 사출 성형의 세단계. 즉 충전, 보 압, 냉각을 모두고려해야한다. 검사체적 방법에 기초한 혼합 유한요소/유한차분방법을 사용 하는 수치 해석적 기법에 의하여 충전과정가 후충전 과정의 유동장 해서을 수행하였다. 일 반화된 헬레쇼 유동을 가정하였고 보압과 냉각과정시의 고본자의 압축성을 고려하였다. 점 도의 전단 변형률의 크기와 온도에 대한 의존성은 개선된 크로스 모델을 사용하여 나타내었 다. Tait에 의해 제안된 상태방정식은 고분자의 온도, 압력, 부피의 상호관계를 묘사하는 좋 은 방법을 제공하였다. 유동해석을 통하여 전 공정에 걸쳐서 온도와 압\ulcorner장의 변화에 대한 데이터를 얻었고 제품의 고체 응력해석의 입력 데이터로 사용하였다. 유한요소응력해석에는 평면 응력요소를 사용하였다. 다양한 형태의 금형에 대해서 공정 변수들을 달리하여 유동장 의 해석과 잔류응력의 계산을 수행하였다. 이로부터 공정조건과 유동장의 관계를 밝히고 최 종 제춤의 잔류 응력에의 영향을 고찰하였다.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.359-365
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• 2008

This paper focused on generation of more accurate DEM and analysis of accuracy. For this, we applied suitable sensor modeling technique for each satellite image and automatic pyramid matching using image pyramid was applied. Matching algorithm based on epipolarity and scene geometry also was applied for stereo matching. IKONOS, Quickbird, SPOT-5, Kompsat-2 were used for experiments. In particular, we applied orbit-attitude sensor modeling technique for Kompsat-2 and performed DEM generation successfully. All DEM generated show good quality. Assessment was carried out using USGS DTED and we also compared between DEM generated in this research and DEM generated from common software. All DEM had $9m{\sim}12m$ Mean Absolute Error and $13m{\sim}16m$ RMS Error. Experimental results show that the DEMs of good performance which is similar to or better than result of DEMs generated from common software.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.4 s.70
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• pp.395-404
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• 2005

This paper presents a reliable numerical procedure for nonlinear time-history analysis of space steel frames subjected to dynamic loads. Geometric nonlinearities of member (P-$\delta$) and frame (P-$\Delta$) are taken into account by the use of stability functions in framed stiffness matrix formulation. The gradual yielding along the member length and over the cross section is included by using a tangent modulus concept and a softening plastic hinge model based on the New-Orbison yield surface. A computer program utilizing the average acceleration method for the integration scheme is developed to numerically solve the equation of motion of framed structure formulated in an incremental form. The results of several numerical examples are compared with those derived from using beam element model of ABAQUS program to illustrate the accuracy and the computational efficiency of the proposed procedure.

• Korean Journal of Remote Sensing
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• v.38 no.5_3
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• pp.939-951
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• 2022

The most important factor in designing autonomous driving systems is to recognize the exact location of the vehicle within the surrounding environment. To date, various sensors and navigation systems have been used for autonomous driving systems; however, all have limitations. Therefore, the need for high-definition (HD) maps that provide high-precision infrastructure information for safe and convenient autonomous driving is increasing. HD maps are drawn using three-dimensional point cloud data acquired through a mobile mapping system (MMS). However, this process requires manual work due to the large numbers of points and drawing layers, increasing the cost and effort associated with HD mapping. The objective of this study was to improve the efficiency of HD mapping by segmenting semantic information in an MMS point cloud into six classes: roads, curbs, sidewalks, medians, lanes, and other elements. Segmentation was performed using various machine learning techniques including random forest (RF), support vector machine (SVM), k-nearest neighbor (KNN), and gradient-boosting machine (GBM), and 11 variables including geometry, color, intensity, and other road design features. MMS point cloud data for a 130-m section of a five-lane road near Minam Station in Busan, were used to evaluate the segmentation models; the average F1 scores of the models were 95.43% for RF, 92.1% for SVM, 91.05% for GBM, and 82.63% for KNN. The RF model showed the best segmentation performance, with F1 scores of 99.3%, 95.5%, 94.5%, 93.5%, and 90.1% for roads, sidewalks, curbs, medians, and lanes, respectively. The variable importance results of the RF model showed high mean decrease accuracy and mean decrease gini for XY dist. and Z dist. variables related to road design, respectively. Thus, variables related to road design contributed significantly to the segmentation of semantic information. The results of this study demonstrate the applicability of segmentation of MMS point cloud data based on machine learning, and will help to reduce the cost and effort associated with HD mapping.