• 대한조선학회논문집
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• 제40권5호
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• pp.26-35
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• 2003

Propellers operating in a given nonuniform ship wake generate unsteady loads leading to undesirable stern vibration problems. The skew is known to be the most proper and effective geometric parameter to control or reduce the fluctuating forces on the shaft. This paper assumes the skew profile as either a quadratic or a cubic function of the radius and determines the coefficients of the polynomial function by applying the simplex method. The method uses the converted unconstrained algorithm to solve the constrained minimization problem of 6-component shaft excitation forces. The propeller excitation was computed either by applying the two-dimensional gust theory for quick estimation or by the fully three-dimensional unsteady lifting surface theory in time domain for an accurate solution. A sample result demonstrates that the shaft forces can be further reduced through optimization from the original design.

• 터널과지하공간
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• 제7권4호
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• pp.334-340
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• 1997

Alpha center theory which was first proposed by Stefanescu has been proved to be effective for the detection of the location of the conductive orebody. A numerical forward modeling was conducted to verify the effectiveness of this method. Field works were carried out along the three profiles in two different areas for the purpose of finding fractured zone which might be accompanied with the presence of the groundwater. And the results were modeled by alpha center method, which was later testified by wellproven 2-dimensional finite difference inversion scheme. Field data could be successfully modeled with this alpha center algorithm, especially for the smooth-varying resistivity models. For the abrupt change of the resistivity values, the alpha center coefficients have a tendency to be negative to simulate the steep resistivity gradients. This method is quite simple and easy for the future applications. The numerical calculation can be performed very quickly with the personal computers.

• 대한기계학회논문집
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• 제17권10호
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• pp.2407-2417
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• 1993

Thermal deformations and stresses due to temperature changes are the serious problems in cryogenic structures such as the torque tube in a superconducting generator, In this paper, the equations of thermal expansion coefficients expressed only by material properties and winding angles are derived for the filament wound composite tubes. The experimental results of thermal contraction of CFRP tubes are compared with those from theoretical approach. Composite tubes with optimally regulated thermal expansion coefficient are designed on the basis of the study for the torque tube in the superconducting generator with temperature distributions varying from 300K to 4.2 K. The filament winding angle of composites resisting thermal stresses properly is sought by the finite element method using layered shell elements. The results show that the composite tubes designed for the requirements in cryogenic environments can effectively cope with the thermal stress problem.

• International Journal of Aeronautical and Space Sciences
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• 제1권1호
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• pp.29-35
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• 2000

A numerical method to simulate Wing-In-Ground(WIG) effects for the wings moving near ground is developed. The aerodynamic analysis scheme for the wings is based on a compressible non-planar lifting surface panel method and the WIG effect is included by images. The thickness-induced effect is implemented into the lifting surface panel method by using the teardrop theory. The numerical simulation is done for the rectangular wings by varying the ground proximity. The present method is validated by comparing the calculated aerodynamic coefficients with other numerical results and measured data, showing good agreements.

• 한국가구학회지
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• 제20권6호
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• pp.599-604
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• 2009

For the search of unified law of moisture movement in wood, moisture distribution of Korean red pine at non-steady state was investigated. We assume that the equilibrium moisture content (EMC) in wood depends on only temperature and relative humidity, it can be control in temperature and humidity chamber. If temperature is constant and humidity or vapor pressure is changed with sin curve shape at adequate cycles, EMC in chamber can be changed as well with sin-curve shape. The setup condition of a non-steady state in humidity control chambers is a constant temperature at $20^{\circ}C$ and 15+10 sin ${\omega}t$ percent EMC. It can be found that the distribution of moisture in the specimen with varying relative humidity are illustrated various types. Moisture in wood is complicated and vibrates with the moisture sorption process. Considering a unified law of moisture movement in wood, it is considered that the most important fact is to search the method of precise diffusion & transfer coefficients.

• 전기학회논문지
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• 제67권11호
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• pp.1506-1511
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• 2018

This study presents a human sensibility evaluation method using neural network and multiple-template method on electroencephalogram(EEG). We used a multi-layer perceptron type neural network as the sensibility classifier using EEG signal. For our research objective, 10-channel EEG signals are collected from the healthy subjects. After the necessary preprocessing is performed on the acquired signals, the various EEG parameters are estimated and their discriminating performance is evaluated in terms of pattern classification capability. In our study, Linear Prediction(LP) coefficients are utilized as the feature parameters extracting the characteristics of EEG signal, and a multi-layer neural network is used for indicating the degree of human sensibility. Also, the estimation for human comfortableness is performed by varying temperature and humidity environment factors and our results showed that the proposed scheme achieved good performances for evaluation of human sensibility.

• Coupled systems mechanics
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• 제5권1호
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• pp.87-100
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• 2016

In this work, an improved semi-analytical technique is adopted to track the dynamic response of thin rectangular plates excited by sequential traveling masses. This technique exploits a so-called indirect definition of inertial interaction between the moving masses and the plate and leads to a reduction, in the equations of motion, of the number of time-varying coefficients linked to the changing position of the masses. By employing this optimized method, the resonance of the plate can be obtained according to a parametric study of relevant maximum dynamic amplification factor. For the case of evenly spaced, equal masses travelling along a straight line, the resonance velocity of the masses themselves is also approximately predicted via a fast methodology based on the fundamental frequency of the system only.

• Structural Engineering and Mechanics
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• 제64권6권
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• pp.683-693
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• 2017

According to a generalized nonlocal strain gradient theory (NSGT), dynamic modeling and free vibrational analysis of nanoporous inhomogeneous nanoplates is presented. The present model incorporates two scale coefficients to examine vibration behavior of nanoplates much accurately. Porosity-dependent material properties of the nanoplate are defined via a modified power-law function. The nanoplate is resting on a viscoelastic substrate and is subjected to hygro-thermal environment and in-plane linearly varying mechanical loads. The governing equations and related classical and non-classical boundary conditions are derived based on Hamilton's principle. These equations are solved for hinged nanoplates via Galerkin's method. Obtained results show the importance of hygro-thermal loading, viscoelastic medium, in-plane bending load, gradient index, nonlocal parameter, strain gradient parameter and porosities on vibrational characteristics of size-dependent FG nanoplates.

• Structural Engineering and Mechanics
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• 제13권3호
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• pp.329-343
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• 2002

In this research, the dynamic stability of an orthotropic elastic conical shell, with elasticity moduli and density varying in the thickness direction, subject to a uniform external pressure which is a power function of time, has been studied. After giving the fundamental relations, the dynamic stability and compatibility equations of a nonhomogeneous elastic orthotropic conical shell, subject to a uniform external pressure, have been derived. Applying Galerkin's method, these equations have been transformed to a pair of time dependent differential equations with variable coefficients. These differential equations are solved using the method given by Sachenkov and Baktieva (1978). Thus, general formulas have been obtained for the dynamic and static critical external pressures and the pertinent wave numbers, critical time, critical pressure impulse and dynamic factor. Finally, carrying out some computations, the effects of the nonhomogeneity, the loading speed, the variation of the semi-vertex angle and the power of time in the external pressure expression on the critical parameters have been studied.

• 한국전문물리치료학회지
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• 제2권1호
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• pp.1-13
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• 1995

The purpose of this study was to examine the inter-rater reliability of the Korean translation of the GMFM(Gross Motor Function Measure). Three licensed physical therapists with varying amounts(2 - 6 years) of clinical experience served as raters. Thirty patients with cerebral palsy were subjects for this study. Subjects were 22 boys and 8 girls, aged 1 to 8 years. Reliability of each dimension and each total score of the GMGM were analyzed using ICCs(intraclass correlation coefficients). The reliability of each dimension score ranged from .76 to .98, with the walking, running, and jumping dimension having higher reliability values. The reliability of the total dimension score was .94. We conclude that the GMFM has inter-rater reliability for assessing gross motor function in patients with cerebral palsy.