• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1147-1158
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• 2008

In this paper, we designed a phase-looking circuit that locks the 16.8 GHz VTDRO to a 700 MHz SAW oscillator using SPD as a phase detector Direct phase locking with loop filter alone causes the problem of lock time, so VTDRO is phase leered by loop filter with the aid of time varying square wave current generator. The current generator is related to the loop filter and needs the systematic toning. In this paper, a systematic design of the current generator and loop filter is presented. The fabricated PLDRO shows a stabilized frequency of 16.8 GHz, a output power 6.3 dBm, and a phase noise of -101 dBc/Hz at the 100 kHz offset.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.398-403
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• 2003

Dynamic Voltage Restorers (DVR)s are known as the best effective and economic means to compensate for voltage sags and swells [1]-[11]. This paper proposes a novel method to generate reference voltages synchronized with the grid whether the line voltages are distorted by a fault or not. The proposed reference wave generator (RWC) looks for the original wave forms from the corrupted line voltages and synthesizes the expected positive sequence reference waves for DVRs. There is no transient problem on the generated reference waves when the line voltages are distorted by the fault.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.56-59
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• 2001

An effective method of detecting inter-turn short circuits on round rotor windings is described. Shorted-turns can have significant effects on a generator and its performance. A method of detecting inter-turn short circuits on rotor windings is described. The approach used is to measure the rate of change of the air-gap flux density wave when the rotor is at operating speed and excitation is applied to the field winding. The inter-turn short circuits sensor for synchronous generator's field winding has been developed. The sensor, installed in the generator air-gap, senses the slot leakage flux of field winding and produces a voltage waveform proportional to the rate of change of the flux. For identification of reliability for sensor, a inter-turn short circuits test was performed at the West-Inchon combined cycle power plant on gas turbine generator and steam turbine generator. This sensor will be used as a detecting of shorted-turn for field winding of synchronous generator. The purpose of this paper is to describe the design and operation of a sensitive inter-turn short circuits detector. In this paper, development of inter-turn short circuits sensor for field winding of synchronous generator and application in a field.

• Proceedings of the KIEE Conference
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• 2009.04b
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• pp.79-81
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• 2009

튜블러 선형 동기발전기는 간단하고 안정적인 구조이며, 구조적으로 수직력이 발생하지 않는다. 본 논문에서는 파력발전에 튜블러 선형 동기발전기를 소개한다. 또한 flat type과 특성비교를 통하여 튜블러 발전기가 파력발전에 적합함을 증명하였다.

• Tribology and Lubricants
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• v.4 no.2
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• pp.60-67
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• 1988

Conventional theory of gear mechanism can't be applied to analyze the harmonic drive due to specific movement of the teeth. This paper deals with an analysis of kinematics and geometry of the tooth engagement of a harmonic drive comprising circular spline, flexspline and wave generator. A theoretical new tooth profile of the flexspline in meshing internal rigid gear with involute profile is obtained. Characteristics of harmonic drive reducer are shown according to parameters such as deviation coefficient, deviation distance, addendum modification coefficient. As an example, the design of harmonic drive with 1:80 reduction ratio is presented.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.95-97
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• 1995

A superconducting current generator, or a superconducting rectifier(SCR) is used as a current source to energize a superconducting magnets in SMES, MRI. We selected a full-wave SCR among various SCR models and analyzed its operational characteristics by computer simulation. In process of pumping the current, the improvement of performance is dependent on how much bigger the open resistance of the switch is in comparison to load coil impedance when one of two switches become active. Faster transfer can he seen in resistive commutation mode by shortening the time elapsed for the resistance to arrive at certain level from zero state. Although recovery time for the switch has no direct effect on current pumping, optimal switch design is needed to increasing operational frequency.

• Journal of Hydrogen and New Energy
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• v.22 no.4
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• pp.552-558
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• 2011

A 50 kW class rotating body type wave energy converter consisted of two floating bodies and a PTO (Power Takeoff) unit is studied. As an wave energy extractor, the body is designed to have a VLCO (Variable Liquid-Column Oscillator) having a liquid filled U-tube with air chambers. Owing to the oscillation of the liquid in the U-tube caused by the air spring effect of the air chambers, the amplitude of response of the VLCO becomes significantly amplified for a target wave period. The PTO converts the rotational moment introduced from the relative motion of the hinged bodies to an hydraulic power by means of a cylinder. A high pressure accumulator, hydraulic motor and a generator are equipped in the PTO to convert the hydraulic power to electric power. A control law for adjusting the oscillation period of the VLCO is proposed for the efficient operation of the VLCO with various wave conditions. It is found that the effect of the air spring has an important role to play in making the oscillation of the VLCO match with the ocean wave. In this way, the wave energy converter equipped with the VLCO provides the most effective mode for extracting energy from the ocean wave.

• Computers and Concrete
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• v.25 no.3
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• pp.245-253
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• 2020

Vibrational analysis in microtubules is examined based on the nonlocal theory of elasticity. The complete analytical formulas for wave velocity are obtained and the results reveal that the small scale effects can reduce the frequency, especially for large longitudinal wave-vector and large circumferential wave number. It is seen that the small scale effects are more significant for smaller wave length. The methods and results may also support the design and application of nano devices such as micro sound generator etc. The effects of small scale parameters can increase vibrational frequencies of the protein microtubules and cannot be overlooked in the analysis of vibrating phenomena. The results for different modes with nonlocal effect are checked.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.277-286
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• 2013

Cross-shore sediment transport is very important factor in the design of coastal structures, and the beach profile is mainly affected by a number of parameters, such as wave height and period, beach slope, and the material properties of the bed. In this study cross-shore sediment movement was investigated using a physical model and various offshore bar geometric parameters were determined by the resultant erosion profile. The experiments on cross- shore sediment transport carried out in a laboratory wave channel for initial base slopes of 1/8, 1/10 and 1/15. Using the regular waves with different deep-water wave steepness generated by a pedal-type wave generator, the geometrical of sediment transport rate and considerable characteristics of beach profiles under storm conditions and bar parameters affecting on-off shore sediment transport are investigated for the beach materials with the medium diameter of $d_{50}$=0.25, 0.32, 0.45, 0.62 and 0.80 mm. Non-dimensional equations were obtained by using linear and non-linear regression methods through the experimental data and were compared with previously developed equations in the literature. The results have shown that the experimental data fitted well to the proposed equations with respect to the previously developed equations.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.15-22
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• 2004

Twin-skeg type stern shapes are recently adopted for very large commercial ships. However it is difficult to apply a CFD system to a hull form having twin-skeg, since grid topology around a twin-skeg type stern is more complicated than that of a conventional single-screw ship, or of an open-shaft type twin-screw ship with center-skeg. In the present study a surface mesh generator and a multi-block field grid generation program have been developed for twin-skeg type stern. Furthermore, multi-block flow solvers are utilized for potential and viscous flow analysis around a twin-skeg type stern The present computational system is applied to a 15,000TEU container ship with twin-skeg to prove the applicability. Wave profiles and wake distribution are calculated using the developed flow analysis tools and the results are compared with towing tank measurements.