• Ocean Systems Engineering
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• v.4 no.1
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• pp.63-82
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• 2014

Declutching control is applied to a hemispherical wave energy converter with direct linear electric Power-Take-Off systems oscillating in heave direction in both regular and irregular waves. The direct linear Power-Take-Off system can be simplified as a mechanical spring and damper system. Time domain model is applied to dynamics of the hemispherical wave energy converter in both regular and irregular waves. And state space model is used to replace the convolution term in time domain equation of the heave oscillation of the converter due to its inconvenience in analyzing the controlled motion of the converters. The declutching control strategy is conducted by optimal command theory based on Pontryagin's maximum principle to gain the controlled optimum sequence of Power-Take-Off forces. The results show that the wave energy converter with declutching control captures more energy than that without control and the former's amplitude and velocity is relatively larger. However, the amplification ratio of the absorbed power by declutching control is only slightly larger than 1. This may indicate that declutching control method may be inapplicable for oscillating wave energy converters with direct linear Power-Take-Off systems in real random sea state, considering the error of prediction of the wave excitation force.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.E
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• pp.373-381
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• 1993

To understand the human exposure levels of volatile halogenated hydrocar-bons in ambient air, a new rapid and convenient analytical method for determination of the compounds in gaseous phase was evaluated and established. The method is based upon passsive diffusion to personal sampler containing adsorbent and solvent extraction followed by purge trap/ on-column cryof-ocusing method. A new method needs no special instrumentation for gas collection because it is based upon the passive diffusion principle. The typical chromatogram obtained in this study proved that rapid and simultaneous determination of target analytes was possible with good resolution. The developed method was successfully applied to determine the volatile halogenated hydrocarbons in indoor air and the values obtained by this new method were compared with those by direct suction method. The concentration of carbon tetrachloride, 1,1,2-trichloroethylene, chloroform showed the values below 400$\mug/m^3$ except the maximum of 1,513$\mug/m^3$ of chloroform. 1,1,1-Trichloroethane showed approximately 1,000 to 5,000$\mug/m^3$ range of diurnal fluctuation in indoor air.

• Journal of Sensor Science and Technology
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• v.29 no.3
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• pp.205-210
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• 2020

The aim of this study is to develop a vertical vibration compensator that attenuates the vertical vibration of ships. The vibration compensator was designed according to the principle of generating vertical excitation forces by rotating two eccentric bodies of the same mass in opposite directions at the same rotational speed. In addition, the structural stability was analyzed using the finite element method. The maximum stress in the drive shaft was 95.6 MPa, which was approximately 35% of the allowable stress of the shaft material (SM45C, 270 MPa). The acceleration signals of the vibrator compensator body and the testbed were determined to evaluate the efficiency of the vibration compensator and the designed excitation forces. Subsequently, the excitation forces were estimated based on the relationship between force and acceleration. The estimated results were very close to the theoretical values with an error of less than 3%.

• Steel and Composite Structures
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• v.43 no.2
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• pp.229-240
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• 2022

The main objective of this work is presenting a mathematical model for the concrete slab with fiber reinforced polymer (FRP) layer under the impact load. Impacts are assumed to occur normally over the top slab and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The structure is assumed viscoelastic based on Kelvin-Voigt model. Based on the sinusoidal shear deformation theory (SSDT), energy method and Hamilton's principle, the motion equations are derived. Applying DQM, the dynamic deflection and contact force of the structure is calculated numerically so that the effects of mass, velocity and height of impactor, boundary conditions, FRP layer, structural damping and geometrical parameters of structure are shown on the dynamic deflection and contact force of system. Results show that considering structural damping leads to lower dynamic deflection and contact force. In addition, increasing the impact velocity of impactor yields to increases in the maximum contact force and deflection while the contact duration is decreased. The result shows that the contact force and the central deflection of the structure decreases and the contact time decreases with assuming FRP layer.

• Earthquakes and Structures
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• v.26 no.6
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• pp.477-487
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• 2024

The interaction between multiple structures through the supporting soil media, known as structure-soil-structure interaction (SSSI), has become an increasingly important issue due to rapid urbanization. There is a need to investigate the effect of SSSI on the structural response of buildings compared to non-interaction analysis (NIA) and soil-structure interaction (SSI) analysis. In the present study, two identical 4-bay×4-bay, three-story RCC buildings are modeled adjacent to each other with a soil domain beneath it to investigate the effect of SSSI on the forces experienced by footings under gravity and seismic load cases. The ANSYS software is used for modeling various non-interaction and interaction models which work on the principle of FEM. The results indicate that in most of the footings, the SSSI effect causes a significant redistribution of forces compared to SSI and NIA under both gravity and seismic load cases. The maximum interaction effect is observed on the footings that are closer to the adjacent building. The axial force, shear force and bending moment values on these footings show that SSI causes a significant increase in these values compared to non-interaction analysis but the presence of adjacent building relieves these forces significantly.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1178-1182
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• 2004

This paper presents web-based virtual laboratory system for electronic and digital circuit experiments. Through our virtual laboratory, the learners will be capable of learning the concepts and theories related to circuit experiments and how to operate virtual experimental equipments such as multimeters, function generators, digital oscilloscopes, DC power suppliers and bread board etc. The proposed virtual laboratory system is composed of important components: Principle Classroom to explain the concepts and theories of electronic and digital circuit operations, Simulation Classroom to provide a web-based simulator to the learners, Virtual Experiment Classroom to provide interactive multimedia contents about the syllabus of off-line laboratory class, Assessment Classroom, and Management System. With the aid of the management System every classroom is organically tied together collaboration to achieve maximum learning efficiency. We have obtained several affirmative effects such as high learning standard, reducing the total experimental hours and the damage rate for experimental equipments.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2326-2336
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• 1996

So most practical combustor is considered to the swirl flame, it is very important to examinate swirl flame structure and combustion characteristics. Recently, attention has been paid to the flame diagnostic by radical luminous intensity. For swirl flame structure and combustion characteristic, reverse flow boundary, temperature, ion current and radical luminous intensity were measured in the double-coaxial swirl combustor which was used principle of multi-annular combustor. This study had three experimental condition, S-type, C-type, SC-type. S-type and C-type flames were formed recirculation zone, but SC-type flame wasn't formed. C-type flame had two recirculation zone. The position with maximum value of ion current and CH-radical, temperature and OH-radical had similarity distribution almost. Therefore, it is possible that the macro structure of flame was measured by radical luminous intensity in the high intensity of turbulent combustion field which was formed by swirl.

• Journal of the Korean Mathematical Society
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• v.46 no.1
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• pp.41-49
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• 2009

Let $\zeta$ be a fixed complex number. In this paper, we study the quantity $S(\zeta,\;n):=mas_{f{\in}{\Lambda}_n}\;|f(\zeta)|$, where ${\Lambda}_n$ is the set of all real polynomials of degree at most n-1 with coefficients in the interval [0, 1]. We first show how, in principle, for any given ${\zeta}\;{\in}\;{\mathbb{C}}$ and $n\;{\in}\;{\mathbb{N}}$, the quantity S($\zeta$, n) can be calculated. Then we compute the limit $lim_{n{\rightarrow}{\infty}}\;S(\zeta,\;n)/n$ for every ${\zeta}\;{\in}\;{\mathbb{C}}$ of modulus 1. It is equal to 1/$\pi$ if $\zeta$ is not a root of unity. If $\zeta\;=\;\exp(2{\pi}ik/d)$, where $d\;{\in}\;{\mathbb{N}}$ and k $\in$ [1, d-1] is an integer satisfying gcd(k, d) = 1, then the answer depends on the parity of d. More precisely, the limit is 1, 1/(d sin($\pi$/d)) and 1/(2d sin($\pi$/2d)) for d = 1, d even and d > 1 odd, respectively.

• Journal of the Korean Institute of Rural Architecture
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• v.21 no.3
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• pp.33-40
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• 2019

Woolyang(月梁) is a beam which whole shape is curved like a so-called moon(月). According to the ${\ll}$Yeongjobeosig(營造法式)${\gg}$, In the case of beams installed under the ceiling of a wooden building, it is used by manufacturing them in Woolyang(月梁) for maximum visual decorative effects as the shape is exposed. In order to achieve the end of a beam that is manufacturing in Woolyang(月梁), it is important to process it in a suitable size and shape for a given situation to achieve a combination with other members around it. However, in the "營造法式", the standard of production of the Woolyang(月梁) is divided into Myeongbog(明?), Chagyeon(箚牽), Pyeonglyang(平梁), and the height of each beam head is divided into 21分$^{\circ}$, 15分$^{\circ}$, 25分$^{\circ}$, but it is not possible to look at any more specific reference. In this paper, try to consider the principle of Woolyang(月梁) manufacturing and its normative contents which were indirectly proposed in the ${\ll}$Yeongjobeosig(營造法式)${\gg}$.

• Child Health Nursing Research
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• v.13 no.1
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• pp.13-20
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• 2007

Purpose: This investigation examined a model to predict body mass index in order to prevent later development of obesity among adolescents. The hypothesized model was developed based on the principle of Social Cognitive Theory that social influences predict perceptions of cognition as well as behavior. Method: The 5,770 adolescents, aged 14-18 who participated in this study came from 11 separate school districts in Busan and Kyungnam province of South Korea. The adolescent surveys were administered in a group setting at the participating school. Of the 5770 surveys, adolescents with more than 10 percent missing data in the entire survey were excluded. The final sample contained 4,527 cases. The adolescents were included 2,250 (49.7%) males and 2,277 (50.3%) females. Data was analyzed Pearson correlation coefficients using SPSS 12 program and structural equation model (SEM) using Maximum Likelihood estimation was employed using Amos 5.0. Results: Social support directly affects cognitive determinants. Cognitive determinants directly affect behavior determinants which directly affect BMI. Cognitive and behavioral factors mediated the relationship between social support and BMI (GFI= 0.984, CFI= 0.974, RMSEA=0.031). Conclusion: Social levels should be supportive to help adolescents have healthier behaviors. This support can be accomplished by providing frequent support to establish positive cognitive factors as the foundation of the solution to prevent overweight and obesity.