• Bulletin of the Korean Chemical Society
• /
• 제25권2호
• /
• pp.267-270
• /
• 2004

The bromate-1,4-cyclohexanedione-ferroin oscillating reactions are uncovered to support two types of wave activities, in which spontaneous formation of circular waves has been achieved after the disappearance of initial waves. The induction period of the revival wave is typically above 10 hours and its dependence on the initial concentrations of reactants is qualitatively different from that of initial waves. In addition to their differences in propagating speed and wavelength, the initial waves and the revival patterns have different colors, suggesting that different reaction mechanisms are involved in the formation of these spatiotemporal behaviors. Our experiments further show that the addition of hydroquinone to the reacting system can significantly shorten the induction time of the revival wave, which implicates that hydroquinone is not only a product in the bromate-1,4-cyclohexanedione-ferroin oscillating reaction but also plays a critical role in the following reactions.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.483-487
• /
• 2011

In the present study, a CFD program based on a finite volume method was developed by using an unstructured polyhedral grid system for the accurate simulation with the complex geometry of computational domain. To simulate the transient flow induced by the moving solid object, the program used a fractional step method and a ALE (Algebric Lagrangian-Eulerian) method. The grid deformation for the moving of solid object were performed with a spring analogy based on the center coordinate of each computational grid. To verify the present program with these methodologies, the numerical results of the flow around the fixed and oscillating circular cylinder were compared with the previous numerical results.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 C
• /
• pp.1999-2001
• /
• 2000

Impulse breakdown voltage characteristics of sulphur-hexafluoride/nitrogen ($SF_{6}-N_{2}$) mixtures were presented. The applied voltages were the positive and negative lightning impulse (1.2/44${\mu}s$) and oscillating impulse ($0.4{\mu}s$/2.08MHz) voltages. The predischarge current was observed to clarify the breakdown mechanism. The electrode system was consisted of plane to plane configuration with a needle-shaped protrusion whose length and diameter are 10mm and 1mm. The measurements were carried out at the gas pressure of mixtures up to 0.5MPa with nitrogen concentrations varying from 5 to 20%. The electrical breakdown in $SF_{6}-N_{2}$ mixtures develops with steplike pulses in leader mechanism. The minimum breakdown voltages for the negative lightning and oscillating impulse voltages were higher than those for the positive.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2003년도 하계학술대회 논문집 B
• /
• pp.756-758
• /
• 2003

In the machine tool industry, direct drive linear motor technology is of increasing interest as a means to achieve high acceleration, and to increase reliability. This paper deals with the characteristics of tubular type linear oscillating actuator with Halbach magnet array. The magnetic field solutions are derived analytically in terms of vector potential, two dimensional cylindrical coordinate system and Maxwell's equations. Motor thrust, flux linkage, back emf are then derived. The results are shown in good conformity with those obtained from the commonly used finite element method. Test results such as thrust measurements are also given to confirm the analysis.

• 전자공학회논문지
• /
• 제51권8호
• /
• pp.178-184
• /
• 2014

자기 변형 기술의 거리 측정을 응용하여, 중력과 액체 밀도에 대응하는 부력의 평형 위치를 측정하는 액체 밀도 센서를 개발하였다. 이 시스템의 정밀도 향상을 위해, 액체 밀도변화에 따른 밀도 센서의 이동거리 사이의 관계식을 유도하고, 이를 이용하여, 액체 밀도 센서의 2 점 보정 방법을 마련하였다. 제작된 액체 밀도 센서 시스템과 유도된 관계식을 사용하여 액체의 밀도들을 측정하였다. 측정된 결과들을 U-tube 진동주기 측정방식의 고 정밀 밀도 측정기(Oscillating U-tube density meter: 분해능 0.000001 g/cc)의 측정결과와 비교하였다. 그 결과 두 액체 밀도 측정 시스템간의 측정 편차가 0.001 g/cc 미만임을 확인하였다.

• Ocean Systems Engineering
• /
• 제4권1호
• /
• pp.63-82
• /
• 2014

Declutching control is applied to a hemispherical wave energy converter with direct linear electric Power-Take-Off systems oscillating in heave direction in both regular and irregular waves. The direct linear Power-Take-Off system can be simplified as a mechanical spring and damper system. Time domain model is applied to dynamics of the hemispherical wave energy converter in both regular and irregular waves. And state space model is used to replace the convolution term in time domain equation of the heave oscillation of the converter due to its inconvenience in analyzing the controlled motion of the converters. The declutching control strategy is conducted by optimal command theory based on Pontryagin's maximum principle to gain the controlled optimum sequence of Power-Take-Off forces. The results show that the wave energy converter with declutching control captures more energy than that without control and the former's amplitude and velocity is relatively larger. However, the amplification ratio of the absorbed power by declutching control is only slightly larger than 1. This may indicate that declutching control method may be inapplicable for oscillating wave energy converters with direct linear Power-Take-Off systems in real random sea state, considering the error of prediction of the wave excitation force.

• 동력기계공학회지
• /
• 제14권6호
• /
• pp.75-82
• /
• 2010

In this study, the topics for free-surface wave simulation, nonlinear hydrodynamic force, and the critical resonance frequency of so-called ${\tau}=U{\omega}/g$=1/4 are discussed. A high-order spectral/boundary element method is newly adapted as an efficient numerical tool. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time domain. In this method, the velocity potential is expressed as the sum of surface potential and body potential. Then, surface potential is solved by using the high-order spectral method and body potential is solved by using the high-order boundary element method. By the combination of these two methods, the wave-making problems by a submerged sphere oscillating with forward speed under the free-surface are solved in time domain.

• 한국해안·해양공학회논문집
• /
• 제23권5호
• /
• pp.345-357
• /
• 2011

최근 지구환경문제와 에너지원의 다각화를 위한 일환으로 파랑에너지를 이용하는 신재생에너지의 기술개발이 유럽과 일본 등을 중심으로 활발히 추진 및 실용화되고 있다. 특히, 케이슨 내의 공기실에서 파랑에 의한 수면의 상하운동으로 유도되는 공기흐름을 이용하는 진동수주형 파력발전시스템은 가장 효율적인 파랑에너지흡수장치로 알려져 있고, 따라서 상업화에 가장 근접한 파력발전장치 중에 하나이다. 본 연구에서는 진동수주형 파력발전구조물에서 터빈(Wells터빈)에 직접 작용하는 공기흐름속도를 2차원 및 3차원수치실험으로부터 검토하며, 이 때 형상의 변화에 따른 공기의 최대흐름속도를 추정하여 진동수주형 파력발전구조물의 최적형상을 논의한다. 수치해석에서는 기체와 액체의 혼상동적현상을 동일한 지배방정식으로 해석하는 혼상류(2상류)수치모델에 기초한 3차원수치파동수로를 적용하였다. 이로부터 입사주기대에 따라 최적형상의 크기가 상이하게 나타나는 것을 확인할 수 있었고, 최소의 반사율이 발생하는 주기 대에서 공기흐름이 최대로 된다는 것을 알 수 있었다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1997년도 춘계학술대회 논문집
• /
• pp.218-223
• /
• 1997

The technique used is the active structural acoutrol (ASAC)approach which involves controlling the acoustic response of a panel-cavity covpled system by applying oscillating force inputs in the form of prezoelectric actuators directly to the flexible panel. The linear quadratic Gaussian control scheme is used for attenuating nosie inside the rectangular enclosure causing by flexible wall vibration. Results indicated the application of control inputs to the radiating wall resukted in considerable noise reductions inside the cavity. Auso,the possibility of application to the more complicated fluid-structure coupled system is verified.

• 대한조선학회논문집
• /
• 제42권4호
• /
• pp.368-378
• /
• 2005

The effects of rotary oscillation on the unsteady laminar flow past a circular cylinder. are numerically investigated in the present study. The numerical solutions for the 20 Wavier-Stokes equation are obtained using a finite volume method Tn the framework of an overlapping grid system. The vortex formation behind a circular cylinder and the hydrodynamics of wake flows for different rotary oscillation conditions are analyzed from the results of numerical simulation. The lock-on region is defined as the region that the natural shedding frequency due to the Karmann Vortex shedding and the forcing frequency due to the forced oscillating a cylinder are nearly same, and the quasi-periodic states are observed around that region. At the intersection between lock-on and non-lock-on region the shedding frequency is bifurcated. After the bifurcation, one frequency fellows the forcing frequency($S_f$) and the other returns to the natural shedding frequency($St_0$). in the quasi-periodic states, the variation of magnitudes and relevant phase changes of $C_L$ with forcing phase are examined.