• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.325-338
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• 2015

Experimental and numerical investigations were conducted to identify the wake characteristics downstream of two vane-type vortex generators over laminar flat plate boundary layer. Experimental study was carried out by using the stereoscopic particle image velocimetry. To describe the flow field around the vortex generator in detail, numerical study was performed. We considered two different planform shapes of vortex generator: triangular and rectangular shape. The height of the generator was chosen to be about the boundary layer thickness at the position of its installation. Two different lengths of the generator were chosen: two and five times the height. Wake measurements were carried out at three angles of attack for each configuration. Wake characteristics for each case such as overall vortical structure, vorticity distribution, and location of vortex center with downstream distance were obtained from the PIV data. Wake characteristics, as expected, were found to vary strongly with the geometry and angle of attack so that no general tendency could be deduced. Causes of this irregular tendency were explained by using the results of the numerical simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1227-1229
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• 2007

In this paper a robust controller using adaptive backstepping technique is proposed to control the position of wind power generation system. To make wind power generation truly cost effective and reliable, advanced and robust control algorithms are derived to on-line adjust the excitation winding voltage of the generator based on both mechanical and electrical dynamics. This method is shown to be able to achieve smooth and asymptotic rotor speed tracking, as justified by analysis and computer simulation.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권2호
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• pp.215-221
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• 2014

To satisfy the high voltage direct current (HVDC) grid connection demand for wind power generation system, a novel topology and control strategy of HVDC grid connection for open-winding permanent magnet synchronous generator (PMSG) based wind power generation system is proposed, in which two generator-side converter and two isolated DC/DC converters are used to transmit the wind energy captured by open winding PMSG to HVDC grid. By deducing the mathematic model of open winding PMSG, the vector control technique, position sensorless operation, and space vector modulation strategy is applied to implement the stable generation operation of PMSG. Finally, the simulation model based on MATLAB is built to validate the availability of the proposed control strategy.

• Journal of international Conference on Electrical Machines and Systems
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• 제2권4호
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• pp.491-497
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• 2013

This paper introduces the high efficiency operation of switched reluctance generator (SRG). The proposed SRG operates under the rated speed. The high efficiency can be obtained by the optimal current shape which can make the total losses minimum. For this purpose, theoretical analysis of the copper and core loss is done. In addition, a modified angle position control (MAPC) method which can get the optimal current shape over wide speed condition is presented. In order to verity the theory, the experimental platform is set up. The feasibility of the theory is verified by the simulation and experimental results. The proposed method is simple, reliable and easy to achieve.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.83-85
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• 1996

Major cause of defects in steam generator tubes at nuclear power plant is the accumulation of magnetite and other byproducts of corrosion in the crevice gap between support plates and tubes. Since damaged tubes result in contamination of the secondary coolant by the radioactive primary coolant, they represent a safety hazard. Early detection of magnetite buildup is, therefore, imperative in order to take remedial measures such as chemical flushing. Although the eddy current testing is being used for the inspection of steam generator tubes, the interpretation of resulting signals is generally a difficult task. This paper uses the phase of sensor coil emf as the test signal to find a way of easier signal interpretation. Numerical study using FEM shows that the shape of resulting signal is good for identifying the relative position of the probe to the support plate, and for discreminating the different shapes and degrees of magnetite buildup in the crevice gap region.

• Journal of Advanced Marine Engineering and Technology
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• 제16권5호
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• pp.6-16
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• 1992

Since world-wide oil shock on 1970s, many large size-low speed diesel engines, instead of steam turbines, are used for the industrial electric power generating plants due to their economic advantage of low specific fuel consumption. But it is very important to control their electric power fluctuation problems for the purpose of smooth parallel operation with existing power plants. In this paper the fluctuation problem of KEPCO Nam-cheju No.1 generator driven by diesel ngine(B & W 7K 60MC, 13931x138.5RPM) is investigated with analysis of torsional vibration of which 4th harmonic component is related to its power fluctuation. The problem can be improved by modification of cylinder arrangement and flywheel position in reverse sequence, equalizing the combustion gas pressure of all cylinder and installation of torsional vibration damper enlarged 30%(Je=7287Kg.m$^{2}$) and high quality balancing of generator rotor.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.734-739
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• 2001

In this paper, we develop a six-axes machining center tool(MCT) and CAD/CAM system. The MCT consists of two mechanical parts, i.e., a X-Y-Z Cartesian coordinate typed MCT and a parallel-typed tilting table. Kinematics and singularity are accomplished to design the parallel-typed tilting table, and CAD/CAM system is developed for the six-axes MCT, which requires the commands of position as well as orientation for machining of complex shape. The CAD/CAM system has a tool path generator, a NC code generator and a graphic simulator. This paper designs the parallel-typed tilting table to meet the desired specification and presents the results of tool path, NC code and graphic simulation.

• 비파괴검사학회지
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• 제25권3호
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• pp.201-208
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• 2005

In this paper, absolute and differential eddy current signals from various defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal changes due to frequency increase are also observed. After studying signal patterns from various defects and frequencies, the analysis of mixed defect signals affected by the presence of a ferromagnetic support plate is attempted. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the slope angle analysis of the signal. Results show that differential signals are useful for locating the position of a defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.216-220
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• 2000

AC Superconducting Generators (ACSG) are featured by 3D magnetic flux distribution, which decreases in the direction of axis. For this reason, when ACSG is optimal designed, 3D magnetic field analysis is required. This paper proposes 2D Finite Element Analysis (FEA) results normalized by 3D FEA according to the position of armature coil and the ratio of field coil width to axial length in order to reduce the analysis time. By using the proposed data, the reasonable 3D FEA results of ACSG can be only predicted by 2D FEA results. The validity of the 3D FEA results is verified by comparison with the experimental results of 30kVA superconducting synchronous generator.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.282-285
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• 2008

In this paper, the numerical analysis of the model without air-guide was carried out in wind power generator. From numerical results, the temperature rise was not satisfied for the class F insulation and the non-uniformity of temperature distribution was a wide difference in heating elements. To improve these problems, the air-guide was installed in front of the coil head of non-drive end(NDE). The short distance between coil head and air-guide was more effective than long distance in cooling performance. Compared to that of the preliminary design, it was found that the cooling performance of the modification design was improved about 12%.