• International Journal of Naval Architecture and Ocean Engineering
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• 제10권5호
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• pp.545-565
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• 2018

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

• 대한기계학회논문집B
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• 제35권6호
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• pp.617-624
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• 2011

본 연구에서는 사각용기 내에서의 자유표면을 갖는 2차원 슬로싱 문제에 대하여 고찰하였다. 용기 내부의 유동은 수평방향의 조화운동을 통해 형성되며, 외부 가진 속도는 u=Asin($2{\pi}ft$)으로 정의 된다. 여기서 u, A�� 그리고 f는 외부로부터 작용하는 가진 속도, 변위 그리고 주파수를 각각 나타낸다. 큰 변위(A~O(1)) 슬로싱 문제의 해석을 위한 실험설비를 구축하였으며, 광범위한 영역에서의 PIV실험을 수행하였다. 실험을 통해 자유표면의 움직임(motion)을 각각 서로 다른 물리적 특성을 갖는 세 가지; 선형 슬로싱의 자유표면의 움직임과 유사한 standing wave motion, 사각용기의 속도가 0을 지나는 순간(the moment of turn-over) 측벽에서 발생하는 run-up motion 그리고 측벽으로부터 내부유체로 점차적으로 전파되는 bore motion으로 분류하였다.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1634-1644
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• 2016

In this paper, a current-fed two-inductor bi-directional DC/DC converter using resonance (CF-TIBCR) and its design method are proposed. The CF-TIBCR has characteristics of low current ripple and a high current rating because of two separated inductors. Also, it achieves zero voltage switching for all switches and zero current switching for switches of a low voltage stage by using the resonant tank. Besides, a voltage spike problem in conventional current-fed converters is solved without the need for an additional snubber or clamping circuits. As a result, the CF-TIBCR features high step-up and high efficiency. Since the proposed converter has difficulty achieving the soft-switching condition when the converter requires the low voltage transfer ratio, a method that varies the number of resonant cycles is adopted to extend the output voltage range with satisfying the soft-switching condition. The principles of the operation characteristics are presented with a theoretical analysis, and the proposed converter is verified through results of an experiment using a laboratory prototype.

• 수산해양기술연구
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• 제35권3호
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• pp.312-322
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• 1999

A ultrasonic transduce with a single acoustic matching layer has been designed as an attempt to increase the bandwidth of underwater transducer. The wideband resonance condition was accomplished by attaching a single matching layer on the front face of a ceramic resonator composed of a piezoelectric bar, a taper part and a head part. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedance and thickness of the matching layer in the water tank.The obtained results are summarized as follows:1. Measured resonant and antiresonant frequencies of the piezoelectric transducer with no matching layer in air were 24.7 kHz and 25.6 kHz, respectively. 2. Two resonant frequencies of the piezoelectric transducer with a single matching layer were 21.7 kHx and 26.9 kHz, respectively, in air and 21.4 kHz and 22.7 kHz, respectively, with a water load.3. Two distinct resonance peaks in the transmitting voltage response(TVR) of the developed transducer were observed at 22.0 kHz and 25.8 kHz, respectively, with center frequency of 24.0 kHz. The values of TVR at these frequencies were 130.1 dB re $1 \muPa$/V at 22.0 kHz and 128.5 dB re $1 \muPa$/V at 25.8 kHz, respectively.Reasonable agreement between the experimental results and the numerical values was achieved.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.484-486
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• 2008

본 논문은 중용량 및 대용량에 적합하며 다중 출력 전원시스템의 슬림화에 유리한 새로운 LLC 공진형 DC/DC 컨버터에 관한 것으로써, 별도의 Post-regulator 및 제어 IC의 추가없이 정밀한 이중출력이 가능한 새로운 방식의 컨버터를 제안한다. 제안된 컨버터는 두 개의 트랜스를 이용하여 각 출력 단에 대한 독립된 두 개의 공진탱크를 갖기 때문에 탱크 설계가 용이하고, 다중출력을 필요로 하는 전원시스템의 소형화 및 슬림화에 유리하다. 또한 두 개의 출력을 각각 주파수와 듀티로 제어함에 따라 Post-Regulator 가 필요 없으며, 이로 인해 기존 LLC 공진형 DC/DC 컨버터에 비해 효율 및 발열 특성이 매우 우수하며, 저가의 컨버터 구현이 가능하다. 최종적으로 제안된 컨버터의 우수성과 타당성 검증을 위해, 실제로 42"" FHD급 PDP 용 전원회로를 위한 시작품을 제작하여 고찰된 실험결과를 제시한다.

• 조명전기설비학회논문지
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• 제29권2호
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• pp.19-26
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• 2015

This paper presents design, fabrication, and performance evaluation of a high voltage power supply for Carbon Nano Tube-based planar light sources. The proposed power supply employs an LLC resonant half-bridge converter and a sixfold voltage-multiplying rectifier. Steady-state characteristics of the voltage-multiplying rectifier are analyzed and used to derive the input-to-output voltage conversion ratio of the power supply. The input-to-output frequency response characteristics of the LLC tank circuit are analyzed and utilized in designing a proto-type power supply which produces a 15 KV output using a 400 V input source. The high-voltage transformer is fabricated using a sectional bobbin structure with an epoxy impregnation, in order to provide sufficient insulation for high voltage operations. The performance of the proposed power supply is confirmed with stable and reliable operations at the 15 KV output from no load to nominal load conditions. The proposed power supply is well suited as an electric ballast required stable operations of Carbon Nano Tube-based planar light sources.

• 한국해양공학회지
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• 제36권1호
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• pp.21-31
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• 2022

In recent years, various studies have been conducted on oscillating-water-column-type wave energy converters (OWC-WECs) with multiple chambers with the objective of efficiently utilizing the limited space of offshore/onshore structures. In this study, a numerical investigation based on a numerical wave tank was conducted on single, dual, and triple OWC chambers to examine the hydrodynamic performances and the energy conversion characteristics of the multiple water columns. The boundary value problem with the Laplace equation was solved by using a numerical wave tank based on a finite element method. The validity of the current numerical method was confirmed by comparing it with the measured data in the previous experimental research. We undertook a series of numerical simulations and observed that the water column motion of sloshing mode in a single chamber can be changed into the piston motion of different phases in multiple OWC chambers. Therefore, the piston motion in the multiple chambers can generate considerable airflow at a specific resonant frequency. In addition, the division of the OWC chamber results in a reduction of the time-dependent variability of the final output power from the device. As a result, the application of the multiple chambers leads to an increase of the energy conversion performance as well as a decrease of the variability of the wave energy converter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.434-436
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• 1996

This paper investigates the optimal design of an electronic ballast of half bridge inverter type in consideration of the variation of ambient temperatures for a 15[W] triple-type compact fluorescent lamp. The performances of electronic ballasts under different values or the capacitance ratio in the resonant tank circuit are compared with each other in the practical temperature range between 15[$^{\circ}C$] and 35[$^{\circ}C$] to determine its optimum value. As a result, the optimum value is found to be such that $C_1/C_2=10$ at which value starting of the lamp is most stable and light output reaches its maximum value with lowest variation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.209-212
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• 2003

This paper proposes a soft-transition control strategy for a three phase ZCS(Zero Current Switching) inverter circuit. Each phase leg of inverter circuit consists of an LC resonant tank, two main switches, and one auxiliary switches. This paper presents design consideration via a study example of a three phase prototype inverter for motor drives. A simple device tester with zero current switching capability is proposed to select eligible auxiliary switches. The principle of operation, feature and design considerations are illustrated and verified through the experiment with a 2.2kW 5kHz IGBT based experimental circuit.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.155-158
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• 2004

This paper proposes a soft-transition control strategy for a three phase ZCS(Zero Current Switching) inverter circuit. Each phase leg of inverter circuit consists of an LC resonant tank, two main switches, and two auxiliary switches. This paper presents design consideration via a study example of a three phase prototype inverter for motor drives. A simple device tester with zero current switching capability is proposed to select eligible auxiliary switches. The principle of operation, feature and design consideration is illustrated and verified through the experiment with a 2.2kW 5kHz IGBT based experimental circuit.