• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.140-148
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• 1992

The free vibration problem of symmetrically laminated composite rectangular plates is formulated based on anisotropic thick plate theory including the effects of shear deformation and rotary inertia. Considering the difficulty of obtaining closed-form solutions, Rayleigh-Ritz analysis using polynomials having the property of Timoshenko beam functions as trial functions is adopted. The boundary conditions elastically restrained against rotation are accomodated as well as classical boundary conditions. From the results of numerical studies, the validity of the present method is verified. And it is also found that the adoption of thick plate theory for the vibration analysis of laminated composite plates is essential because of the relatively large shear deformation effect, and that the convergence of the Rayleigh quotient to the stationary value is less rapid in anisotropic composite plates than that in the orthotropic ones due to more complicated mode shapes of the former.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.230-235
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• 1997

Coupling loss variation as the shape of fiber ends and the fiber arrangement in a fiber Fabry-Perot cavity, formed with two optical fibers with dielectric mirror coatings on their ends, is analyzed. For the intended features it is assumed that one of two fibers is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. In this assumption, it was turned out that the coupling loss at the cavity length of 15 ${\mu}{\textrm}{m}$ is less than 0.5% even with tilt angle of 0.2$^{\circ}$, curvature error of 70 ${\mu}{\textrm}{m}$, cavity length error of 8 ${\mu}{\textrm}{m}$, and lateral alignment error of 0.5 ${\mu}{\textrm}{m}$. Thus, low loss and high-finesse fiber Fabry-Perot filters whose cavity length is greater than several ${\mu}{\textrm}{m}$ can be obtained easily if the receiving fiber end is properly formed.

• Journal of the Korean Geotechnical Society
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• v.28 no.12
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• pp.87-98
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• 2012

A sonar sensor system of a new socket roughness profiling system (SRPS) which can measure the socket roughness of the large-diameter drilled shafts under the in-situ condition was developed and verified. In model tests, the salinity, temperature, and high-turbidity have been changed for simulating the in-situ borehole water conditions. From the test results, it was found that the sonar sensor can measure the distance within an accuracy of 1mm. Because of the wave form characteristics of sonar sensor, the relative error exists in case of the inclined and curved surface, however, the shape of specimen was confirmed relatively exactly using the developed sonar sensor. Moreover, the salinity, temperature, and high-turbidity did not affect the measured data of socket roughness.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.6
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• pp.330-336
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• 2004

In this work, in order to obtain the detailed information about lightning electromagnetic pulses, the electric fields radiated from multiple lightning return strokes were measured and analyzed statistically. The electric field measuring system consists of a hemisphere antenna of 30cm in diameter, integrator and data acquisition device, and its frequency bandwidth ranges from 200Hz to 1.56MHz, and the sensitivity is 0.96㎷/V/m. The electric field signals are digitized every 200ns with the transient signal analyzer having the resolution of 12-bit and the recording length of 5 kilowords and are registered at personal computer. As a result, the electric fields produced by the first return stroke begin with a slow initial part or front, which starts just after or during the last stepped leader. On the average the rise times of the electric fields for the positive first, second and third strokes are 4.21${\mu}\textrm{s}$, 3.94${\mu}\textrm{s}$ and 2.75${\mu}\textrm{s}$, respectively, and those for the negative first, second and third strokes are 3.46${\mu}\textrm{s}$, 3.15${\mu}\textrm{s}$ and 2.79${\mu}\textrm{s}$, respectively. The zero-crossing times of the electric fields for first return strokes range from about 10 to 80${\mu}\textrm{s}$. The mean zero-crossing times for subsequent return strokes are shorter than those for first lightning return strokes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.1
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• pp.51-58
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• 2001

Recently, DC-DC converters significantly increase the total losses as rising switching frequency. Trnditional soft switching technique for reducing switching losses even increase voltage/Clment stress of switch In this paper, Resonant circuit for soft switching is connected in parallel with power stage and only operates just before tum-on of the main sWItch. Therefore, ills doesn't affect the total circuit QI'||'&'||'pound;ration. The object of tIns paper is to make the linearized equivalent loss mxleIs. and to analyze the total losses by experiment. ZVT-PWlvI converter designed with 170-260[V] input, 400[V] 5[A] output, and 100[kHz] switching frequency is tested respectively with 500[W], 1[kW], 1.5[kW], and 2[kW] loads. The total losses in input 220[V], 2[kW] load are analyzed by usirm the linearized equivalent loss models.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.10a
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• pp.241-242
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• 2009

There are marry ships and marine structures and also has marry differences on according to the shape and the interval of hulls to the purpose. the multi-submerged body needs appropriate distance between the hulls because of the optimum hull form. thus, through this paper, the flow characteristics behind the multi-submerged body according os the distance ration between the hulls and various angles of attack was conducted.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.1
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• pp.35-41
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• 2003

In this paper statistics on the radiation field waveforms produced by stepped leaders just prior to lightning return strokes were described. As a parameter of stepped leader pulse characteristics, the time interval between the final leader pulse and return stroke peak, the pause time between stepped leaders, the ratio of the final leader peak to the return stroke peak and the stepped leader pulse width at half maximum were examined. The average time intervals between the final leader pulse and return stroke peak were about 16.2 and 14.8$mutextrm{s}$ for the positive and negative polarities, respectively. When the stepped leader approaches closely to ground, the time interval between leader steps was decreased and the mean value was about 17$mutextrm{s}$, and the present results were in reasonable agreement with the data observed in Florida and Japan. The large fraction of the ratios of the final stepped leader pulse to the lightning return stroke peak were distributed over the range from 5 to 35% and in average the ratio of the final leader pulse to the return stroke peak was 17.4$\pm$11.9% for the positive and 18.5$\pm$9.4% for the negative electric field waveforms. In addition, the mean pulse widths at half maximum of the stepped leaders are 1.4Us with a standard deviation of 0.9 for the positive Polarity and 2.2us with a standard deviation of 1.2 for the negative polarity, respectively.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.1
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• pp.33-38
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• 1997

Generally, various semiconductor switching devices for power systems are used in battery chargers for electric vehicle. When these used, it takes the problems of transient-current or distortion of waveforms in power systems near by battery chargers because of harmonics and large peak-current, low power factor, etc., caused by the non-linearity of these devices. Recently, power factor control, line current peak-cut, harmonics reduction which was ignored in past is more and more important. In this paper, to solve those problems we will improve the characteristics of voltage rising and propose the high power factor converter circuit for battery chargers. Our proposed system convert commutated voltage to AC resonant wave in high frequency inverter and rectify the link voltages passed high-frequency transformer and transfer the DC voltages. Especially, the effect using these converter system can be improved very large by power factor control and we have to verify the possibilities of improvement through the experiment of Pb-Acid battery application.

• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.3
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• pp.122-134
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• 1994

The objective of this study is to provide with the hydrometeological and probabilistic characteristics of the storms and winds of typhoons that have been passed through the Korea peninsula during the last twenty-three years since 1961. The paths and intensities of the typhoons were analyzed. Fifty weather stations were selected and the rainfall and wind data during typhoon periods were collected. Rainfall data were analyzed for the patterns and probabilistic distributions. The results were presented to describe the areal distributions of probabilistic characteristics. Wind data were also analysed for their probabilistic distributions. The results obtained from this study can be summarized as follows: 1. The most frequent typhoon path that have passed through the Korean peninsula was type E, which was followed by types CWE, W, WE, and S. The most frequent typhoon intensity was type B, that was followed by A, super A, and C types, respectively. 2. The third quartile typhoon rainfall patterns appear most frequently followed by the second, first, and quartiles, respectively, in Seoul, Pusan, Taegu, Kwangju and Taejon. The single typhoon rainfalls with long rainfall durations tended to show delayed type rainfall patterns predominantly compared to the single rainfalls with short rainfall durations. 3. The most frequent probabilistic distribution for typhoon rainfall event is Pearson type-III, followed by Two-parameter lognormal distribution, and Type-I extremal distribution. 4. The most frequent probability distribution model of seashore location was Pearson type-III distribution. The most frequent probability distribution model of inland location was two parameter lognormal distribution. 5. The most frequent probabilistic distribution for typhoon wind events was Type-I xtremal distribution, followed by Two-parameter lognormal distribution, and Normal distribution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.146-152
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• 2016

This paper describes a multi-physics analysis of a high resolution winding type resolver and rotary transformer using FEM (Finite Element Method). The rotary transformer boosts the input voltage to a high voltage which can be input into the rotor windings of the resolver. Through multi-physics models of the transformer and resolver, the characteristics of the output signals for the resolver system with high resolution can be derived. Moreover, the circuit model of the interface part between the transformer and resolver should be considered, because of the calculation of the input current to the resolver. The winding type resolver is composed of 32x and 1x stator windings for high resolution. Then, the output signals of the stator windings, which make sinusoidal SIN and COS waves with a $90^{\circ}$ phase difference, are verified.