• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.315-323
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• 2015

Nowadays, it is expected that mobility loads such as electric railways and electric vehicles will be penetrated gradually and affect on the power system stability by their load characteristics. Various researches have been carried out about electric vehicles for the recent decade though the load of electric railway could be forecasted because of the specified path and timetable, is a field with a long historic background. Some precise 5th polynomial equations are required to analyze the power system stability considering mobility load to be increased in the immediate future while the electric railway dispatching simulator uses load models with constant power and constant impedance for the system analysis. In this paper, seasonal urban railway load models are established as the form of 5th polynomial equations and substation load modeling methods are proposed merging railway station load models and general load models. Additionally, load management effects by the load modeling are confirmed through the case studies, in which seasonal load models are developed for Seoul Subway Line No. 2, Gyeongui Line and Airport Railroad and the substation load change is analyzed according to the railway load change.

• The Journal of Korean Physical Therapy
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• v.24 no.4
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• pp.241-246
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• 2012

Purpose: We investigated the effect of postural stability and balance with foot orthotics in hemiplegic patients. Methods: The subjects enrolled in this study were 16 hemiplegic patients who were examined for balance ability, weight distribution, and limits of stability with or without foot orthotics insole. Balance was measured according to a stance position by BIORESCUE: static balance open eyes (SEO), static balance close eyes (SEC), dynamic balance open eyes (DEO), dynamic balance close eyes (DEC), right and left weight distribution (RLWD), anterior and posterior weight distribution (APWD) and limit of stability (LOS). The data were analyzed with SPSS window version 18.0 (IBM Co., Armonk, NY, USA). Results: The results were of significant changes to the SEO (p<0.05), RLWD (p<0.05), APWD (p<0.05), and LOS (p<0.05). The SEC, DEO and DEC were not found to be statistically significant. Conclusion: It was found that foot orthotics affected the balance for hemiplegic patients. Therefore, it is thought to help fall prevention to measure the balance ability.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.355-366
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• 2018

One of the significant problems in the design of onshore pipelines in seismic areas is their stability in case of liquefaction. Several model tests and numerical analyses allow investigating the behavior of pipelines when the phenomenon of liquefaction occurs. While experimental tests contribute significantly toward understanding the liquefaction mechanism, they are costly to perform compared to numerical analyses; on the other hand, numerical analyses are difficult to execute, because of the complexity of the soil behavior in case of liquefaction. This paper reports an overview of the existing computational methods to evaluate the stability of onshore pipelines in liquefied soils, with particular attention to the development of excess pore water pressures and the floatation of buried structures. The review includes the illustration of the mechanism of floating and the description of the available calculation methods that are classified in static and dynamic approaches. We also highlighted recent trends in numerical analyses. Moreover, for the static condition, referring to the American Petroleum Institute (API) Specification, we computed and compared the uplift safety factors in different cases that might have a relevant practical use.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.179-187
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• 2013

Floating production storage and offloading (FPSO) facilities are used at most of the offshore oil fields worldwide. FPSO usage is expected to grow as oil fields move to deeper water, thus requiring the reliability and stability of mooring wires and risers in extreme environmental conditions. Except for the case of predictable attack angles of external loadings, FPSO facilities with turret single point mooring (SPM) systems are in general use. There are two types of turret systems: permanent systems and disconnectable turret mooring systems. Extreme environment criteria for permanent moorings are usually based on a 100-year return period event. It is common to use two or three environments including the 100-year wave with associated wind and current, and the 100-year wind with associated waves and current. When fitted with a disconnectable turret mooring system, FPSOs can be used in areas where it is desirable to remove the production unit from the field temporarily to prevent exposure to extreme events such as cyclones or large icebergs. Static and dynamic mooring analyses were performed to evaluate the stability of a spider buoy after disconnection from a turret during cyclone environmental conditions.

• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.1
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• pp.9-20
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• 2019

Korea's R&D investment has significantly increased in recent years. However, the efficiency of R&D investment is still in question. In order to examine the ways to improve the efficiency of R&D investment, this paper presents dynamic analysis on both quantitative and qualitative efficiency of R&D projects. A Data Envelopment Analysis(DEA)/Window method is used to analyze static and dynamic efficiencies of Industrial Material R&D projects in Korea from 2012 to 2016. As a result, statistically significant differences between quantitative and qualitative efficiency have been found. It has been observed that characteristics of Decision Making Units(DMUs) have an impact on both static and dynamic efficiencies. In particular, textile and ceramic projects showed relatively stable qualitative efficiency for a short-term perspective, while steel and chemical projects showed such stability for a long-term perspective. Among the types of project principals, universities showed relatively stable efficiency, compared with private sectors and research institutes. The results of this paper can be used as a guideline to manage the performance and stability of R&D projects' efficiency.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.45 no.1
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• pp.1-7
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• 2019

We introduce to prepare liquid crystalline emulsion composed of cetearyl alcohol, cetyl palmitate, sorbitan palmitate, sorbitan olivate, ceramide and so on which can enforce interface between oil-based particle and water phase. In terms of structural analysis, the stability of the liquid crystalline emulsion including ceramide, which is immisible ingredient, at high temperature was proved by polarized microscope, cryo-SEM, small-angle x-ray scattering, in addition to viscometer and static light scattering by physical analysis.

• Advances in nano research
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• v.16 no.5
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• pp.445-458
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• 2024

The objective of this paper is to present free vibration and static stability analyses of rotating composite beams reinforced with carbon nanotubes (CNTs) under uniform thermal loads. Beam structural equations and CNT-reinforced composite (CNTRC) beam formulations are derived based on Timoshenko beam theory (TBT). The temperature-dependent properties of the beam material, such as the elastic modulus, shear modulus, and material density, are assumed to vary over the thickness according to the rule of mixture. The beam material is modeled as a mixture of single-walled carbon nanotubes (SWCNTs) in an isotropic matrix. The SWCNTs are aligned and distributed in the isotropic matrix with different patterns of reinforcement, namely the UD (uniform), FG-O, FG-V, FG- Λ and FG-X distributions, where FG-V and FG- Λ are asymmetric patterns. Numerical examples are presented to illustrate the effects of several essential parameters, including the rotational speed, hub radius, effective material properties, slenderness ratio, boundary conditions, thermal force, and moments due to temperature variation. To the best of the authors' knowledge, this study represents the first attempt at the finite element modeling of rotating CNTRC Timoshenko beams under a thermal environment. The results are presented in tables and figures for both symmetric and asymmetric distribution patterns, and can be used as benchmarks for further validation.

• Journal of Welding and Joining
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• v.8 no.1
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• pp.31-42
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• 1990

Arc must be stable during welding first of all other factors for obtaining sound weldment, especially in the automation of welding process. Arc stability is somewhat sophisticated phenomenon which is not clearly defined yet. In consumable electrode welding, the voltage and current variation due to metal transfer enables to assess arc stability. Recently, statistical analyses of the voltage and current waveform factors are performed to assess the degress of arc stability which is assessed and controlled by operator's own experience by now. But, considering the increasing need and the trend of automation of welding process, it is necessary to monitor arc stability in real-time. In this sutdy, the modified stability index composed of two voltage and current wvaeform factors (arc time and short circuit time) reduced from four factors (arc time, short circuit time, average arc current and average short circuit current) in Mita's index by the welding electrical circuit modeling is proposed and verified by experiments to be well estimating arc stability in the static sense. Also, the recursive calculation form estimating present arc stability in the dynamic sense is developed for real-time estimation. The results of applying the recursive index during welding show good estimation of arc stability in real-time. Therefore, the results of this study offers the mean for real-time control arc stability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.9
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• pp.856-861
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• 2010

In this work, experiments on hybrid sounding rocket were conducted to investigate the aerodynamic characteristics and analyze longitudinal static stability. Tests were performed on 1/10 scale models of sounding rocket through Mach number ranging from 1.75 to 2.5 and for angle of attack from $0^{\circ}$ to $6^{\circ}$. Aerodynamic forces and moments were measured by means of a 4 component internal balance. With measured forces and moments, static stability characteristics of rocket were calculated. Tests were made for three models with different length to determine the effect of body length. The visualization of shock waves was carried out by Schlieren optical system to observe variations of shock waves with Mach number and angle of attack.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.50-55
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• 2005

An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The laws of flight control system utilize RSS criteria in both longitudinal and lateral-directional axes to achieve performance enhancements. Particularly, the design of longitudinal control laws for utilizing RSS methods greatly affects the performance of the aircraft in Air-to-Air Tracking and Air-to-Ground modes, which improves weapon delivery. In the area of Air-to-Air Tracking, the development of longitudinal control laws aids in the fine tracking and gross acquisition of other aircraft. This paper proposes that new concept of longitudinal control law introduce in order to improve fine tracking performance in air-to-air tracking maneuver. Result of HQS pilot simulation and flight test, fine tracking performance improve without degradation of gross acquisition when new concept of control law is applied.