• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.6
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• pp.23-28
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• 2020

A non-linear vibration isolation system composed of a non-linear spring and a linear damper was presented in a previous study. The advantage of the proposed isolator is the simple structure of the system. When the base of the isolator is harmonically excited, the response component of the mass at the excitation frequency was approximated using three different methods: linear approximation, harmonic balance, and higher-order frequency response functions (FRFs). The method using higher-order FRFs produces significantly more accurate results compared with the other methods. The error between the exact and approximate responses does not increase monotonously with the excitation amplitude and is less than 2%.

• Journal of The Korean Association For Science Education
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• v.12 no.3
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• pp.91-107
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• 1992

The Purpose of this study was to present the procedures and methods of ordering theory,and to search for a learning hierarchy among science process skills in each Piagetian cognitive reasoning level. One of the purpose of this is not to determine the clear and exact hierarchy but rather to demonstrate how ordering theoretic methods and procedures can be used to determine the hierarchy of logical relationships among a set of test items or the testing of a hypothesized hierarchy. Ordering theory was used to analyze five science process skills collected from 509 high school students. Ordering Theory has as its primary intent either the testing of hypothesized hierarchies among items at the determination of hierchies among items. Hierarchical relationships were identified within five science process skills. The results will be helpful in giving useful inform at ions to classroom teachers and science curriculum developer.

• Communications for Statistical Applications and Methods
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• v.23 no.4
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• pp.335-341
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• 2016

Interval censored failure time data often occurs in an observational study where a subject is followed periodically. Instead of observing an exact failure time, two inspection times that include it are made available. Several methods have been suggested to analyze interval censored failure time data (Sun, 2006). In this article, we are concerned with a binary time-varying covariate whose changing time is interval censored. A modified estimating equation is proposed by extending the approach suggested in the presence of a missing covariate. Based on simulation results, the proposed method shows a better performance than other simple imputation methods. ACTG 181 dataset were analyzed as a real example.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.74-80
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• 2001

The estimation of recurrence interval for fault activity and earthquake is an important input parameter for seismic hazard assessment. In this study, the methods of recurrences interval estimation were reviewed and tentative calculation was performed for age dating data which have uncertainty. Age dating data come from previous studies of Ulsan fault system which is a well developed lineament in the southeastern part of korean Peninsula. Age dating for fault gouges, parent rocks, Quaternary sediments and veins were carried out by several researchers through various methods. Recurrence interval for fault activity was estimated on the basis of the age dating data of minor fault gouge and sediments during past 3Ma. The estimated recurrence interval was about 430-500 ka. Exact estimation of recurrence interval for fault activity need to compile more geological data and fault characteristics such as fault length, amount of displacement, slip rate and accurate fault movement age. In the future, the methods and results of fault recurrence interval estimation should be considered for establishing the criteria for domestic active fault definition.

• Journal of Mechanical Science and Technology
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• v.16 no.5
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• pp.619-632
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• 2002

In recent study on design of experiments, the complicate metamodeling has been studied because defining exact model using computer simulation is expensive and time consuming. Thus, some designers often use approximate models, which express the relation between some inputs and outputs. In this paper, we review and compare the complicate metamodels, which are expressed by the interaction of various data through trying many physical experiments and running a computer simulation. The prediction model in this paper employs interpolation schemes known as ordinary kriging developed in the fields of spatial statistics and kriging in Design and Analysis of Computer Experiments (DACE) model. We will focus on describing the definitions, the prediction functions and the algorithms of two kriging methods, and assess the error measures of those by using some validation methods.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.9
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• pp.875-882
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• 2007

In order for a vehicle to follow a predetermined trajectory accurately, its position must be estimated accurately and reliably. In this thesis, we propose trajectory tracking control methods for unmanned vehicle and a positioning system using ultrasonic wave. The positioning problem is an important part of control problem for unmanned navigation of a vehicle. Dead Reckoning is widely used for positioning of vehicle. However this method has problems because it accumulates estimation errors. We propose a new method to increase the accuracy of position estimation using the Ultrasonic Satellite System (USAT). It is shown that we will be able to estimate the position of vehicle precisely, in which errors are not accumulated. And proposed trajectory tracking control methods include both a new path planning method and a lateral control method for vehicle. The experimental results show that the proposed methods enables exact vehicle trajectory tracking even under various environmental factors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1153-1160
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• 2005

Many methods of spot weld modeling have been developed to increase efficiency and guarantee the robustness fer the CAE analysis. In this research they are introduced and the performance is compared in a viewpoint of stiffness and durability. For evaluating the performance a multi-spot welded specimen as well as two single welded specimen is used. The results show that the CWELD element considering 'patch to patch' is stiffer than other modeling methods in stiffness and more conservative in durability. It also offers simple modeling and since it is much easier to maintain the orrhogonality of the BAR element expressing a nugget, we can obtain more exact reaction forces and moments in a nugget. Therefore the CWELD element is the most excellent in the assessment of durability.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.709-715
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• 1999

To optimize a heating and cooling system, we need an exact solution lot radiant heat transfer in any form of room or building. This paper describes the solution method of view factor by the area weighted average and graphical method to calculate the radiant heat exchange or daylighting level in any form of room or building. This study shows that the area weighted average and graphical methods have many points of merits(calculation speed, correctness and calculation capability in an arbitrary form of room shapes etc.) compared with existing methods

• Communications for Statistical Applications and Methods
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• v.23 no.6
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• pp.555-562
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• 2016

Interval censored data often occur in an observational study where the subject is followed periodically. Instead of observing an exact failure time, two inspection times that include it are available. There are several methods to analyze interval censored failure time data (Sun, 2006). However, in the presence of competing risks, few methods have been suggested to estimate covariate effect on interval censored competing risk data. A sub-distribution hazard model is a commonly used regression model because it has one-to-one correspondence with a cumulative incidence function. Alternatively, Klein and Andersen (2005) proposed a pseudo-value approach that directly uses the cumulative incidence function. In this paper, we consider an extension of the pseudo-value approach into the interval censored data to estimate regression coefficients. The pseudo-values generated from the estimated cumulative incidence function then become response variables in a generalized estimating equation. Simulation studies show that the suggested method performs well in several situations and an HIV-AIDS cohort study is analyzed as a real data example.

• Communications for Statistical Applications and Methods
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• v.26 no.3
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• pp.315-323
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• 2019

Panel data sets have recently been developed in various areas, and many recent studies have analyzed panel, or longitudinal data sets. Often a dichotomous dependent variable occur in survival analysis, biomedical and epidemiological studies that is analyzed by a generalized linear mixed effects model (GLMM). The most common estimation method for the binary panel data may be the maximum likelihood (ML). Many statistical packages provide ML estimates; however, the estimates are computed from numerically approximated likelihood function. For instance, R packages, pglm (Croissant, 2017) approximate the likelihood function by the Gauss-Hermite quadratures, while Rchoice (Sarrias, Journal of Statistical Software, 74, 1-31, 2016) use a Monte Carlo integration method for the approximation. As a result, it can be observed that different packages give different results because of different numerical computation methods. In this note, we discuss the pros and cons of numerical methods compared with the exact computation method.