• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2292-2300
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• 2018

A field-circuit coupling model of a typical faulty generator is established to correct through-bolt end-region overheating and breakdown failure in a tubular hydro-generator. Using the model, eddy current loss and electromagnetic forces on through bolts under normal and failure conditions are analyzed and compared and the natural frequency of a through bolt is determined. Based on the analysis results, the causative mechanism of failure is revealed and targeted improvement design measures are proposed. The numerical results are found to be consistent with the actual fault characteristics, validating the design measure improvements. The results are useful in improving the design and manufacturing standards and enhancing the operational reliability of large tubular hydro-generators.

• 한국해안·해양공학회논문집
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• 제22권5호
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• pp.333-343
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• 2010

목포해역에서 조위와 조류 관측자료를 분석하여, 낙조류 우세 조류특성을 보이는 것을 확인하였으며 낙조류 우세를 발생하는 물리적 요인에 대해 검토하였다. 노출한계수심, 바닥마찰응력 산정방법, 해안 매립, 조석의 진폭, 비선형 조석, 와점성계수와 목포해역의 낙조류 우세현상의 관련성에 대해서 2차원 해수유동 모형을 적용하여 자세히 조사하였다. 다양한 조건에 대한 모의결과로부터 노출한계수심과 와점성계수는 모의결과에 거의 영향을 주지 않으며, 바닥마찰응력이 증가함에 따라 조류의 비선형성이 증가하여 낙조류 우세현상이 나타나는 것을 확인할 수 있었다. 간사지가 미치는 영향은 간사지가 육지로 바뀌면 낙조류 우세가 심해지고, 간사지가 바다로 바뀌면 낙조류 우세가 사라지는 것을 확인할 수 있었다. 그동안 목포해역에서 진행되어온 해안매립사업은 낙조우세현상을 심화시켜 왔음을 확인할 수 있었으며, 비선형 조석은 비대칭 조류를 생성하는 데 결정적인 역할을 하여 조류의 비대칭성인 강한 목포해역에서 조류를 모의할 때는 개방경계 조위에 비선형조석을 포함해야 함을 확인할 수 있었다.

• Journal of the korean society of oceanography
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• 제37권3호
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• pp.169-177
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• 2002

An eddy-resolving free-surface primitive-equation model with nonlinear terrain-following coordinates is established to study the exchange of water masses among the Asian marginal seas and their adjacent waters. A curvilinear coordinate system is used to generate the horizontal grid with a variable resolution for the regional oceans from $5^{\circ}$S to $45^{\circ}$N and $100^{\circ}$E to $155^{\circ}$E. The higher resolution region has about a 10 km by 10 km grid covering the complex geometry of the coastal marginal seas, while the lower resolution region has about a 30 km by 30 km grid covering the eastern Pacific. The model is initialized by the Levitus annual climitology and forced by the monthly mean air-sea fluxes of momentum, heat, and freshwater derived from the Comprehensive Ocean-Atmosphere Data Set. High-resolution and low-viscosity are identified as the key factors for a better representation of the exchange of waters through narrow straits and passages between the marginal seas and their adjacent waters. The dynamics of the loop currents and eddies in the South China Sea and Celebes Sea are examined in detail. It has found that the anticyclonic loop and detached eddies from the Kuroshio through the Luzon Strait play an important role in transporting warm and salty water into the South China Sea, while the cyclonic circulation of the Mindanao Current in the Celebes Sea plays a role in contributing cold water to the Indonesian throughflow. The deep undercurrent of the western Pacific is shown to provide fresher water to the South China Sea and Celebes Sea. These modeling results suggest that the exchange processes via the narrow straits and passages are of fundamental importance to the maintenance of water masses for the marginal sea region.

• 한국해양학회지:바다
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• 제24권3호
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• pp.429-435
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• 2019

연안에서 해표면고도를 정확하게 측정하도록 특별히 설계된 SARAL/Altika위성에 의해 관측된 해류를 비교 검정하기 위해 2015년 3월부터 2년간 위성추적 뜰개가 동해 북부 해상에 투하되었다. 해표면 고도 측정 위치에서 반경 20 km 이내에 위치한 뜰개(30분 간격으로 GPS로 위치 관측)와 비교한 결과, 수심 200 m 보다 얕은 해역에서 외해와 유사하게 높은 상관관계를 가진 것으로 나타나, 해류의 직접 관측이 어려운 동해 북부의 연안류의 시간 변동을 관측할 수 있게 되었다. 리만 해류는 일년 년중 시베리아 연안을 따라 남하하는 해류로 관측되었으며, 북한 한류는 여름철에만 남향하는 해류를 보였다. 북한 한류는 무수단곶 이남에서는 주로 남향류를, 무수단곶 이북에서는 무수단곶 근해에서의 에디 존재 유무에 의해 방향이 결정되는 것으로 연구되었다.

• 한국화재소방학회논문지
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• 제16권2호
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• pp.8-13
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• 2002

유도가열 기술은 담금질, 단조를 위한 예열, 용융 그리고 요리 등과 같은 산업 전반에 걸쳐서 아주 폭넓게 사용되는 기술이다. 본 논문에서는 IH-JAR의 효과적인 설계를 위하여 자계 및 열 해석을 하였다. IH-lAR의 내부자계는 3차원 축대칭 유한요소법을 사용하여 해석하였으며, 열원은 IH-JAR 내부에서 유도된 와전류에 의하여 발생되고, 열은 열원과 열방정식을 사용하여 계산되어진다. 또한, IH-JAR의 온도분포를 시간과 투자율에 따라 제시하였다.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권1호
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• pp.34-38
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• 2005

The finite element method is very flexible for new shapes and provides flux distribution, magnetomotive force, eddy currents, and torques. However, it requires lengthy computational time in order to achieve desired accuracy. The magnetic equivalent circuit method takes less computation time than the finite element method. Therefore, the finite element method is mainly used to confirm the completed design. The magnetic equivalent circuit method is convenient for complicated analysis of the transient state of the induction motor. The magnetic equivalent circuit method is restricted to only one direction of magnetic flux. In this paper, the construction elements (that is, stator iron, rotor iron, yoke, air gap, etc.) of the squirrel cage induction motor were represented by a flux tube and the air gap magnetomotive force was calculated by the magnetic equivalent circuit method. Starting transient torque and phase current of the squirrel cage induction motor were verified by the theoretical calculation and the experiment.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.78-83
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• 2002

Since the KSTAR superconducting magnet structure should be maintained at a cryogenic temperature of about 4 K, even a small amount of heat might be a major cause of the temperature rise of the structure. The Joule heating by eddy currents induced in the magnet structure during the KSTAR operation was found to be a critical parameter for designing the cooling scheme of the magnet structure as well as defining the requirements of the refrigerator for the cryogenic system. Based on the Joule heating calculation, it was revealed that the bulk temperature rise of the magnet coil structure was less than 1 K. The local maximum temperature especially at the inboard leg of the TF coil structure increased as high as about 21 K for the plasma vertical disruption scenario. For the CS coil structure, the maximum temperature was obtained from the PF fast discharging scenario. This means that the vertical disruption and PF fast discharging scenarios are the major scenarios for the design of TF and CS coil structures, respectively. For the reference scenario, the location of maximum temperature spot changes according to the transient current variation of each PF coil.

• Progress in Superconductivity
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• 제8권1호
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• pp.122-126
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• 2006

This paper presents experimental and numerical investigation on heat generation of a bulk HTS for application to a 100 kWh Superconductor Flywheel Energy Storage System(SFES) bearing. An experimental device is manufactured to reproduce varying magnetic field conditions that a bulk HTS may experience during the operation of the 100 kWh SFES. The bulk HTS is directly cooled by a cryocooler while the heat is generated by the eddy currents created by varying magnetic fields induced by a coil. In order to design the cryocooling system for the 100 kWh SFES project, a preliminary experiment to investigate the actual cooling load variation under AC magnetic field has been carried out. In the experiment, two different copper holders were designed and tested. Several temperature sensors were installed on each component of the assembly and the temperatures were measured for several operating conditions of the 100 kWh SFES. The experimental investigation on the thermal response of the bulk HTS and its holder is considered to be a valuable step fur the successful materialization of a large-scale SFES.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.144-146
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• 2005

Dual electromagnetic sensor is used for sensing the weld line. The sensor consists of excitation and two sensing coil wound over the ferro-magnetic core. By using the dual sensor, the effect of noise is minimized. It is based on the generation of eddy currents in the welding plate by passing current through the excitation coil. The sensor can be used to track the butt joints having no gap between them, where a vision based sensor fails to track. Sensor sensitivity depends on the number of coil turns, frequency of excitation, distance of a sensor from the work piece, diameter of core, etc. The whole system consists of a sensor, a signal processing board, a motion controller and a personnel computer (PC). The raw sensor signal is processed using the signal processing board. It consists of amplification, rectification, filtering, averaging, offset adjustment, etc. Based on sensor data, the motion controller adjusts the position of a welding torch.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1040-1049
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• 1996

The high loading combustion is accomplished by making the turbulent intensity strong and the scale small in the premixed combustor. The Da-mkoler number, which is decreased by short turbulent characteristic time or by long chemical reaction time, can make the distributed reaction flame. So we developed a doubled jet burner for high loading combustion. The doubled jet burner was designed to make the scale of the flame small by the effect of impingement and increasing shear stress with doubled jet. We investigated the turbulence characteristics of unburned mixture and visualized several flames with the typical schlieren photography. Then we studied the influence of several factors that related the scale of flame. Consequently, the doubled jet burner can make the eddy very small. And we can obtain the detail information of the flame scale through ADSF(the Average Distance between Successive Fringes) in the micro- schlieren photography. The ADSF is not a exact flame scale, but it has qualitative trend with increasing turbulent intensity. The ADSF is diminished remarkably with increasing turbulent intensity. The reason is that strong turbulent intensity makes the flame zone thick and flamelets numerous. We can confirm this fact by the signal analysis of ion currents.