• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.180-180
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• 2023

To improve global risk management, understanding the characteristics and distribution of precipitation is crucial. However, obtaining spatially and temporally resolved climatic data remains challenging due to sparse gauge observations and limited data availability, despite the use of satellite and reanalysis products. To address this challenge, merging available precipitation products has been introduced to generate spatially and temporally reliable data by taking advantage of the strength of the individual products. However, most of the existing studies utilize all the available products without considering the varying performances of each dataset in different regions. Comprehensively considering the relative contributions of each parent dataset is necessary since their contributions may vary significantly and utilizing all the available datasets for data merging may lead to significant data redundancy issues. Hence, for this study, we introduce a site-specific precipitation merging method that utilizes the Quadruple Collocation (QC) approach, which acknowledges the existence of error-cross correlation between the parent datasets, to create a high-resolution global daily precipitation data from 2001-2020. The performance of multiple gridded precipitation products are first evaluated per region to determine the best combination of quadruplets to be utilized in estimating the error variances through the QC approach and computation of merging weights. The merged precipitation is then computed by adding the precipitation from each dataset in the quadruplet multiplied by each respective merging weight. Our results show that our approach holds promise for generating reliable global precipitation data for data-scarce regions lacking spatially and temporally resolved precipitation data.

• Journal of applied mathematics & informatics
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• v.6 no.3
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• pp.697-726
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• 1999

In this paper we develop a now procedure to control stepsize for linear multistep methods applied to semi-explicit index 1 differential-algebraic equations. in contrast to the standard approach the error control mechanism presented here is based on monitoring and contolling both the local and global errors of multistep formulas. As a result such methods with the local-global stepsize control solve differential-algebraic equation with any prescribed accuracy (up to round-off errors). For implicit multistep methods we give the minimum number of both full and modified Newton iterations allowing the iterative approxima-tions to be correctly used in the procedure of the local-global stepsize control. We also discuss validity of simple iterations for high accuracy solving differential-algebraic equations. Numerical tests support the the-oretical results of the paper.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.6
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• pp.529-536
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• 2004

Autonomous navigation of an indoor mobile robot using the global ultrasonic system is presented in this paper. Since the trajectory error of the dead-reckoning navigation grows with time and distance, the autonomous navigation of a mobile robot requires to localize the current position of the robot, so that to compensate the trajectory error. The global ultrasonic system consisting of four ultrasonic generators fixed at a priori known positions in the work space and two receivers on the mobile robot has the similar structure with the well-known satellite GPS(Global Positioning System), and it is useful for the self-localization of an indoor mobile robot. The EKF(Extended Kalman Filter) algorithm for the self-localization is proposed and the autonomous navigation based on the self-localization is verified by experiments.

• Journal of the Korean Solar Energy Society
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• v.30 no.2
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• pp.16-21
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• 2010

Computer simulation of buildings and solar energy systems are being used increasingly in energy assessments and design. This paper discusses the possibility of using sunshine duration data instead of global hourly solar irradiation (GHSI) data for localities with abundant data on sunshine duration. For six locations in South Korea where global radiation is currently measured, the global radiation was calculated using Sunshine Duration Radiation Model (SDRM), compared and analyzed. Results of SDRM has been compared with the measured data on the coefficients of determination (R2), root-mean-square error (RMSE) and mean bias error (MBE). This study recommends the use of sunshine duration based irradiation models if measured solar radiation data is not available.

• Journal of the Korean Solar Energy Society
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• v.38 no.3
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• pp.1-20
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• 2018

It is a very important and fundamental process to know accurately the intensity of the solar energy coming into the installed module considering the tilted angle. Europe and the US commonly use a program called PVsyst to convert the global horizontal irradiation to global irradiation on tilted plane. There are two types of models that PVsyst uses to convert to irradiation on tilted plane. In this paper, Perez model, which is a decomposition model and Perez model, which is a transposition model used in PVsyst, are applied based on global horizontal irradiation and global irradiation on tilted plane measured in a specific area. The comparison of the decomposition model shows the effect of the transpostion model on global irradiation on tilted plane conversion by comparing the ratio of the horizontal diffuse irradiation amount of the Watanabe model which are highly trusted in Asia and the Perez model. The comparison of transposition model confirm the error between the measured data and the calculated value which is applied Perez model to global horizontal irradiation decomposed by Perez model and Watanabe model. Based on the two comparisons, This paper propose a method to confirm the reliability of transposition model and reduce the error when PVsyst is used in Korea.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.5
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• pp.120-127
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• 1998

Differential inequalities occurring in problems of obstacle contact problems are recast into variational inequalities and analyzed by finite element methods. A new a posteriori error estimator, which is essential in adaptive finite element method, is introduced to capture the errors in finite element approximations of these variational inequalities. In order to construct a posteriori error estimates, saddle point problems are introduced using Lagrange parameters and upper bounds are provided. The global upper bound is localized by a special mixed formulation, which leads to upper bounds of the element errors. A numerical experiment is performed on an obstacle contact problem to check the effectivity index both in a local and a global sense.

• Structural Engineering and Mechanics
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• v.4 no.1
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• pp.1-8
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• 1996

A new error measure for a static finite element analysis is proposed. This error measure is a modification to the Zienkiewicz and Zhu energy norm. The new error estimator is a global error measure for the analysis and is independent of finite element model size and internal stresses, hence it is readily transportable to other error calculations. It is shown in this paper the the new error estimator also produces conservative error measurements, making it a suitable procedure to adopt in commerical packages.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.10
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• pp.977-987
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• 2012

One of the most significant errors in the pseudo-range measurement performance of GNSSes (Global Navigation Satellite Systems) is their multipath error for high-precision applications. Several schemes to mitigate this error have been studied. Most of them, however, have been focused on the GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal that was designed in the 1970s and is still being used for civil navigation. Recently, several modernized signals that were especially conceived to more significantly mitigate multipath errors have been introduced, such as Time Multiplexed and Composite Binary Offset Carrier (TMBOC and CBOC, respectively) signals. Despite this advantage, however, a problem remains with the use of TMBOC and CBOC modulations: the ambiguity of BOC (Binary Offset Carrier)-modulated signal tracking. In this paper, a novel unambiguous multipath error mitigation scheme for these modernized signals is proposed. The proposed scheme has the same complexity as HRCs (High Resolution Correlators) but with low ambiguity. The simulation results showed that the proposed scheme outperformed or performed at par with the HRC in terms of their multipath error envelopes and running averages in the static and statistical channel models. The ranging error derived by the mean multipath error of the proposed scheme was below 1.8 meters in an urban area in the statistical channel model.

• Journal of Satellite, Information and Communications
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• v.8 no.2
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• pp.62-67
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• 2013

Recently, users have been receiving LBS(Local Based Service) which provides various services. The LBS uses positioning information from satellites with using GPS(Global Positioning System). However, due to satellite signal's characteristics which are reflection and refraction in urban areas, users get unexpected positioning information error, expecially if there are so many tall buildings in a small area. To solve this problem, this paper offers a post-processing algorithm. It is consisted of users' direction vectors and positioning information. The positioning information with error is designed to be put on the direction vector. Through a car driving test in urban areas, we've got 11.1m(43%) improved result and demonstrated the superiority of its algorithm.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.10
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• pp.23-33
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• 2012

This paper is a study on precise point positioning using global navigation satellite system. This paper studies inherent barriers of global navigation satellite system such as increase in shadowed areas and positioning errors when signals cannot be received due to various environmental factors. It analyzes performance of various receivers, changes in number of satellite and DOP(Dilution of Precision) following changes in environment such as center of a road, side of a road, residential area, high building, and alleys. It also studies changes in positioning error. The objective of this study lies on understanding the range of positioning error following changes in environment and the cause of error, and enhancing the reliability and safety of the global navigation satellite system.