• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.34-39
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• 2015

Experimental studies were conducted on the liquid sloshing characteristics in a spherical tank covered with a flexible membrane. A spherical acrylic tank with 145.2 mm in radius was used as a test tank, and it was half-filled with water. Silicon membranes with 0.2 mm thickness were used as a test membrane with plane or hemispherical types. The test tank was harmonically excited in a vertical direction by an electro-dynamic exciter. In this case, a parametric instability vibration comes up when the excitation frequency is twice the natural frequency. Parametric instability regions of natural modes were measured for three cases, i.e. liquid surface is free, covered with plane membrane and hemi-spherical membrane.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.8
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• pp.529-535
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• 2000

In this paper, a current control system of a single phase PWM AC/DC converter using a reduced-order Luenberger observer without source voltage sensors is proposed. The sinusoidal input current and unity input power factor are realised based on the estimated source voltage performed by the reduced-order Luenberger observer using actual currents and DC link voltage. The poles of the reduced-order Luenberger observer are placed in the left half plane of s-plane by the pole-placement method in order to acquire the stability of the observer. The magnitude and the phase of the estimated source voltage are used to accomplish the unity power factor. The proposed method is implemented by DSP(Digital Signal Processor). Experimental Results verify that the reduced-order observer estimates the source voltage without the estimation error and the control system accomplishes the unity power factor, and constant DC link voltage.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1613-1614
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• 2006

In this paper, a $4{\times}4$ rectangular patch array antenna operated at 20 GHz is implemented for the satellite communication. Two $2{\times}2$ subarrays are designed and more efficient $2{\times}2$ subarray is used for the design of $4{\times}4$ patch array. The sixteen patch antennas and microstrip feeding line are printed on the single-layered substrate. The spacing between the array elements is chosen to be $0.736{\lambda}$. HPBW (Half-Power Beam Width) is 17.6 degrees in the E-plane and 18.7 degrees in the H-plane with a gain of 17.2SdBi in the simulation results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.5-8
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• 1997

A study on the electrical conduction characteristics of the ultrathin organic films is one of the important factors for the development of molecular electronic devices. The Langmuir- Blodgett(LB) technique has recently been attracted interest as a method of the deposition ultrathin films. We hate fabricated N-docosyl N\`-methyl viologen-diTCNQ(DMVT) anion radical LB film and investigated the molecular orientation and electrical conduction characteristics. We have measured infrared transmission-reflection spectra. The alkyl chain is found to he well-ordered with the tilt angle of 13$^{\circ}$ with respect to the substrate surface normal and the TCNQ plane is tilted at 76$^{\circ}$ the surface normal. In ESR spectrum, we confirmed that a half-amplitude linewidth is clearly dependent on the incident angle, which indicates conducting species change. The in-plane conductivity of 31 lagers is approximately 1.33$\times$10$^{-6}$ S/cm. The ohmic behaviour was observed below 0.6 V, when current-voltage(I-V) characteristics was measured verically.

• Journal of the Optical Society of Korea
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• v.4 no.1
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• pp.1-6
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• 2000

Adaptive optics(AO) removes or compensates the distortion caused by a turbulent atmosphere or medium. A wavefront sensormeasures the distortion, on which the correction of AO is based. A new idea of pupil plane wavefront sensing, which consists of a relay lens and a pyramidal-shaped prism, was previously proposed. This paper reviews the idea of pupil wavefrontsensing and presents prism, was previously proposed. The simulation shows that pupilwavefront sensing provides full wavefront sensing when the intensity peak of PSF is located within half of the Airy radius from the apex of the sensor. Adding to this, the sensor is shown to have optimum sensor output with a finite bevel size of the pyramidal prism.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.50-58
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• 2000

A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• Advances in nano research
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• v.12 no.4
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• pp.405-414
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• 2022

In this study, the elastic plane problem of a layered composite containing an internal or edge crack perpendicular to its boundaries in its lower layer is examined using numerical analysis. The layered composite consists of two elastic layers having different elastic constants and heights. Two bonded layers rest on a homogeneous elastic half plane and are pressed by a rigid cylindrical stamp. In this context, the Finite Element Method (FEM) based software called ANSYS is used for numerical solutions. The problem is solved under the assumptions that the contacts are frictionless, and the effect of gravity force is neglected. A comparison is made with analytical results in the literature to verify the model created and the results obtained. It was found that the results obtained from analytical formulation were in perfect agreements with the FEM study. The numerical results for the stress-intensity factor (SIF) are obtained for various dimensionless quantities related to the geometric and material parameters. Consequently, the effects of these parameters on the stress-intensity factor are discussed. If the FEM analysis is used correctly, it can be an efficient alternative method to the analytical solutions that need time.

• Advances in aircraft and spacecraft science
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• v.4 no.6
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• pp.711-727
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• 2017

This article is concerned with a two-dimensional problem of micropolar generalized thermoelasticity for a half-space whose surface is traction-free and the conductive temperature at the surface of the half-space is known. Theory of two-temperature generalized thermoelasticity with phase lags using the normal mode analysis is used to solve the present problem. The formulas of conductive and mechanical temperatures, displacement, micro-rotation, stresses and couple stresses are obtained. The considered quantities are illustrated graphically and their behaviors are discussed with suitable comparisons. The present results are compared with those obtained according to one temperature theory. It is concluded that both conductive heat wave and thermodynamical heat wave should be separated. The two-temperature theory describes the behavior of particles of elastic body more real than one-temperature theory.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.11-19
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• 2018

Propagation of the generalized Rayleigh waves in an elastic half-space covered by an elastic layer for different initial stress combinations and imperfect contact conditions is investigated. Three-dimensional linearized theory of elastic waves in initially stressed bodies in plane-strain state is employed, the corresponding dispersion equation is derived and an algorithm is developed for numerical solution to this equation. Numerical results on the influence of the initial stress patterns and on the influence of the contact conditions are presented and discussed. The case where the external forces are "follower forces" is considered as well. These investigations provide some theoretical foundations for the study of the near-surface waves propagating in layered mechanical systems and can be successfully used for estimation of the degree of the bonded defects between layers, fault characteristics and study of the behavior of seismic surface waves propagating under the bottom of the oceans.

• Advances in aircraft and spacecraft science
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• v.7 no.1
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• pp.41-52
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• 2020

The effect of relaxation times is studied on plane waves propagating through semiconductor half-space medium by using the eigen value approach. The bounding surface of the half-space is subjected to a heat flux with an exponentially decaying pulse and taken to be traction free. Solution of the field variables are obtained in the form of series for a general semiconductor medium. For numerical values, Silicon is considered as a semiconducting material. The results are represented graphically to assess the influences of the thermal relaxations times on the plasma, thermal, and elastic waves.