• 한국해양환경ㆍ에너지학회지
• /
• 제17권2호
• /
• pp.146-152
• /
• 2014

선형발전기와 연성된 원통형 부이의 수직운동으로부터 파랑에너지를 추출하는 파력발전장치의 설계과정을 소개하였다. 최대 파워는 최적조건($c_{PTO}=b_T$, ${\omega}={\omega}_N$)에서 발생하며, 공진조건시 부이의 수직운동 고유주파수와 속도스펙트럼의 피크 주파수를 일치시키지 않고 의도적으로 고유주파수를 15% 크게 설정하면 추출파워의 최대값을 더욱 높일 수 있다. 이러한 방법을 통하여 추출 파워의 증가와 함께 부이의 흘수를 낮추고 동시에 PTO 감쇠력을 줄일 수 있기 때문에 발전장치 제작 비용을 낮출 수 있는 부수적인 효과를 얻을 수 있었다.

• 전력전자학회논문지
• /
• 제18권3호
• /
• pp.225-231
• /
• 2013

This paper presents an improved signal processing technique in the square-wave-type voltage injection method for IPMSM sensorless drives. Since the sensorless method based on the square-wave voltage injection does not use low-pass filters to get an error signal for estimating rotor position and allows the frequency of the injected voltage signal to be high, the sensorless drive system may achieve an enhanced control bandwidth and reduced acoustic noise. However, this sensorless method still requires low-pass and band-pass filters to extract the fundamental component current and the injected frequency component current from the motor current, respectively. In this paper, these filters are replaced by simple arithmetic operations so that the time delay for estimating the rotor position can be effectively reduced to only one current sampling. Hence, the proposed technique can simplify its whole signal process for the IPMSM sensorless control using the square-wave-type voltage injection. The proposed technique is verified by the experiment on the 800W IPMSM drive system.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제9권1호
• /
• pp.25-34
• /
• 2017

The concentric dual-buoy Wave Energy Converter (WEC), which consists of external buoy (hallow-cylinder) with toroidal appendage and cylindrical internal buoy within the moon-pool is suggested in this research and its performance in various wave conditions is studied. The Linear Electric Generator (LEG), consisting of a permanent magnet and coils, is used as a direct Power Take-Off (PTO) system. To maximize the electrical energy extracted from the PTO system, the relative heave motions between the dual buoys must be highly amplified by the multiple resonance phenomena of dual-buoy and internal-fluid motions. The high-performance range can be widened by distributing those natural frequencies with respect to the peak frequency of the wave spectrum. The performance of the newly developed dual-buoy WEC was measured throughout the systematic 1:5.95-model test in regular and irregular waves conducted in a wave tank at Seoul National University. The model-test results are also validated by an independently developed numerical method.

• 한국구조물진단유지관리공학회 논문집
• /
• 제5권4호
• /
• pp.215-225
• /
• 2001

Stress waves monitored on the surface of structures under various loading conditions can provide useful information on the structural health status. In this paper, stress waves are measured by several sensors when a steel beam is impacted by a ball drop. The sensors used include the piezo-electric film Sensor, the electrical strain gage, and the ultrasonic transducer, and special attention is given to the pieza film sensor. The wavelet transform is used for the time-frequency analysis of dispersive waves propagating in the beam. The velocities of the wave produced in the team due to the lateral impact is found to be frequency-dependent and identified as the flexural wave velocity based on the comparisons with the Timoshenko beam theory. A linear impact site identification method is developed using the flexural wave, and the impact sites of the beam can be accurately estimated by the piezo film sensors. It is found that the piezo film sensor is appropriate for sensing stress waves due to impact and for locating impact sites in the beam.

• Journal of Electrochemical Science and Technology
• /
• 제10권2호
• /
• pp.104-114
• /
• 2019

Energy is an essential driving force for modern society. In particular, electricity has become the standard source of power for almost every aspect of life. Electric power runs lights, televisions, cell phones, laptops, etc. However, it has become apparent that the current methods of producing this most valuable commodity combustion of fossil fuels are of limited supply and has become detrimental for the Earth's environment. It is also self-evident, given the fact that these resources are non-renewable, that these sources of energy will eventually run out. One of the most promising alternatives to the burning of fossil fuel in the production of electric power is the proton exchange membrane (PEM) fuel cell. The PEM fuel cell is environmentally friendly and achieves much higher efficiencies than a combustion engine. Water management is an important issue of PEM fuel cell operation. Water is the product of the electrochemical reactions inside fuel cell. If liquid water accumulation becomes excessive in a fuel cell, water columns will clog the gas flow channel. This condition is referred to as flooding. A number of researchers have examined the water removal methods in order to improve the performance. In this paper, a new water removal method that investigates the use of vibro-acoustic methods is presented. Piezo-actuators are devices to generate the flexural wave and are attached at end of a cathode bipolar plate. The "flexural wave" is used to impart energy to resting droplets and thus cause movement of the droplets in the direction of the traveling wave.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 하계학술대회 논문집 D
• /
• pp.2347-2349
• /
• 2004

The iron loss in electric machines takes large part of machine losses and the reduction of iron loss brings the increase of the efficiency. In the rotating machines, however it is very difficult to calculate result because the measuring processes are very complex and laborious. As is well known, the relation between the flux density B and the magnetic field intensity H relation is not linear. For the iron loss, B and H must be measured and usually B becomes the reference wave(sine wave) and the following H is measured using H-coil. To make the B as sine wave, B is controlled by some devices. The error is controlled to become zero by the proposed algorithm which uses the bisection algorithm. The experiments are compared with the simulation results, and they show acceptable agreements.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 1999년도 학술대회논문집-국제 전기방전 및 플라즈마 심포지엄 Proceedings of 1999 KIIEE Annual Conference-International Symposium of Electrical Discharge and Plasma
• /
• pp.141-144
• /
• 1999

This paper offer fundamental ones about insulation diagnosis with electromagnetic wave, when discharges occurred. To simulate Partial-Discharge(PD), It is used needle-plane electrode in air. As the voltages applied, measure the electromagnetic wave with monopole antenna and analysis its fundamental characteristics, then, acquired data were operated. The results presented as the form of graph, and the magnitude of charge when occurred PD simultaneously. In conclusion, when the magnitude of charge over 100[pC], the electric field strength changed, and then the magnitude of charge and the electric field strength increased samely.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.49-51
• /
• 2004

The iron loss in electric machines takes large part of machine losses and the reduction of iron loss brings the increase of the efficiency. In the rotating machines, however it is very difficult to calculate the iron loss and to get the exact experiment result because the measuring precesses are very complex and laborious. As is well known, the relation between the flux density B and the magnetic field intensity H relation is not linear. For the iron loss, B and H must be measured and usually B becomes the reference wave(sine wave) and the following H is measured using H-coil. To make the B as sine wave, B is controlled by some devices. The error is controlled to become zero by the proposed algorithm which uses the bisection algorithm. The experiments are compared with the simulation results, and they show acceptable agreements.

• Nuclear Engineering and Technology
• /
• 제43권2호
• /
• pp.175-186
• /
• 2011

Previous evaluations of the safety of the Ulchin Nuclear Power Plant in the event of a tsunami have the shortcoming of uncertainty of the tsunami sources. To address this uncertainty, maximum and minimum wave heights at the intake of Ulchin NPP have been estimated through a parametric study, and then assessment of the safety margin for the intake has been carried out. From the simulation results for the Ulchin NPP site, it can be seen that the coefficient of eddy viscosity considerably affects wave height at the inside of the breakwater. In addition, assessment of the safety margin shows that almost all of the intake water pumps have a safety margin over 2 m, and Ulchin NPP site seems to be safe in the event of a tsunami according to this parametric study, although parts of the CWPs rarely have a margin for the minimum wave height.

• Journal of Plant Biology
• /
• 제29권1호
• /
• pp.1-10
• /
• 1986

Intra- and inter-specific protoplast fusion of tobacco (Nicotiana tabacum cv. Virginia 115) and pea (Pisum sativum cv. Sparkle) were carried out in highly inhomogeneous alternating electric fields. Under the electric field of alternating current (AC, sine wave), 600 V/cm and 800 kHz for tobacco protoplast, and 600 V/cm and 700 kHz for pea protoplasts, the protoplasts were aggregated in pearl chains. Intra-specific protoplast fusions were most effectively induced within the aggregates of tobacco and pea, respectively, by the additional application of a single high field pulse of direct current (DC, square wave) at 1 kV/cm for 50 $mutextrm{s}$. Inter-specific fusions between protoplasts of the two plants were most effectively induced in the electric field of 600 V/cm and 700 kHz, and square wave pulse at 1 kV/cm for 50 $mutextrm{s}$. The duration of the pulse over the electrical breakdown voltages was simulated from 1 to 100 $mutextrm{s}$ in both tobacco and pea protoplast. The yield of the electrofusion products was significantly high (above 60%), compared with that (20%) of the standard fusion method by polyethylene glycol (PEG) 4,000, and the viability of electrofused protoplasts was above 70%, but that of PEG-fused protoplasts 8~16%, when determined by Evan's blue staining method.