• Proceedings of the KSR Conference
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• 2004.06a
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• pp.690-695
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• 2004

In order to develop a high speed train, various conditions have been considered. Fatigue strength assessment by the fluctuation of pressure is an important one. In this study, the fluctuation and frequency of pressure is measured when KHST(Korean High Speed Train) passes through tunnels in the Kyung-Bu high-speed line. And the characteristics of pressure fluctuation is analysed and formulated. The results of analysis are as follows. The train entering speed and fluctuation value are related. The pressure increasing is generated in proportion to train velocity at leading car. When two train is passing through the tunnel, the pressure value is $1.5\~2$ times higher than one train is passing. The damping ratio of pressure fluctuation is about $92\%$. The number of pressure fluctuation in a tunnel is 4 to 6 times. The result in this study would be a good guidance to calculate the fatigue life and the reliability index of body structure.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.89-95
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• 2005

This paper intends to identify experimentally the relationship between transverse vibration behavior of a spinning disk and high-frequency fluctuation in the driving torque. A testrig has been developed using a CD-ROM disk, a driving motor with torque-varying capability and a power transmission belt and a laser vibrometer was employed to measure the transverse vibration displacements of the disk for a certain range of the spinning speed. The results show that the spinning speed and the magnitude and frequency of the torque fluctuation affect the stability of the disk. In other word, the torque fluctuation causes the instability of the disk at several ranges of the spinning speed below the critical speed and its effects become larger as the disk spins faster or the magnitude of torque fluctuation becomes bigger. The experimental results are found to be in good agreement with analytical estimation.

• Proceedings of the KSR Conference
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• 2003.10a
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• pp.181-186
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• 2003

In order to develop a high speed train, various conditions have been considered. Fatigue strength assessment by the fluctuation of pressure is an important one. In this study, a numerical simulation has been performed to estimate the fluctuation and frequency of pressure when KHST(Korean High Speed Train)passes through tunnels in the Kyung-Bu high-speed railway. The simulation was based on KHST running the Kyung-Bu high-speed line with the speed of 350km/h and the interval of 10 minute headway. And the tunnel entrance speed was estimated by TPS program. Therefore, the fluctuation and frequency of pressure is expressed in Weibull distribution function in the above running situation. The result in this study would be good guidance to calculate the fatigue life and the index of reliability of body structure. We are going to conduct more study to measure the real value of the pressure of the carbody passing through tunnels, to assess the fatigue reliability and to develop method ＆ procedure for the fatigue reliability design.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.1
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• pp.21-28
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• 2002

This paper intends to investigate the effects of speed fluctuation caused by the cogging torque in permanent magnetic motors on the stability of the transverse vibration for a spinning disk. Based on the Kirchhoff\`s plate theory and the assumed mode methods, a set of discretized equations of motion were derived for an annular disk rotating with a harmonically varying speed. Then, a perturbation method using the multiple time scales was employed and stability boundaries were determined explicitly in terms of the magnitude and frequency of speed fluctuation, a nominal sped and the modal characteristics of the disk. It is found that parametric resonance occurs at several speed ranges and a single mode or a combination of two modes are involved to cause instability. It is also observed that unstable regions become broadened as the spinning speed increases or two modes are combined in parametric instability. As numerical simulations, stability analysis of a conventional CD-ROM drive was performed. Results of this work can e used as guidelines for motor design and operations with low vibration.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.23-31
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• 1996

The crankshaft speed fluctuation was measured every crank angle. In order to detect the misfire, the engine and the dynamometer were considered as a single- degree of freedom system. From this modeling, the detection criteria were derived and examined by the engine test. By this method the single misfire or multiple misfires can be detected. Even on the condition of low load and higher speed than 3000rpm, where it was difficult through the other methods, misfire detection was carried out steadily. From this results, the method proposed by this paper proved reasonable.

• Journal of the Korean Institute of Navigation
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• v.14 no.2
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• pp.15-31
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• 1990

Recently, there is a tendency to design the large full ships with lower-powered engine as the means for energy saving in ship's navigation at seas. Such a lower-powered ship is anticipated to show the different propulsive performance in rough seas, because the fluctuation of main engine load of lower powered ship is relatively large as compared with higher-powered ship is relatively large as compared with higher-powered ship. The fluctuation of propeller load is nonlinear at racing condition in waves. It is due to the variation of inflow velocity into propeller, the propeller immersion and the characteristics of engine governor. In this paper, the theoretical calculation of the nominal speed loss and the numerical simulation for the nonlinear load fluctuation of a model ship in rough seas are carried out. From the results of calculation, the following are discussed. (1) The ratio of nominal speed loss to the speed in still water. (2) The manoeuvring ability of ship and the operational ability of main engine in a seaway. (3) A method of the evaluation for the fluctuation of propeller torque and revolution on the engine characteristics plane. (4) The effect of engine governor characteristics on the propeller load fluctuation.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.15-21
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• 1996

Recently speed control system of the towing carriage have been modified by applying a personal computer in the Ship Model Towing Tank of Seoul National University. With this system the carriage speed could be controled precisely in coincidently with a prescribed speed diagram to evaluate the effect of slight towing speed fluctuation caused by some residual current or standing waves which have believed as trivial phenomena in the towing tank. It is found that the slight speed fluctuation of the carriage could lead to serious error in measurement of resistance test of a ship.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.166-172
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• 1996

This paper presents the characteristics of the crankshaft speed fluctuations. To analyze them, the speed waveforms were measured both at the flywheel and at the front end of the engine. The speed waveform measured at the flywheel shows better result than at the front end one, because of the torsional vibration and the auxiliary components. And the patterns of the speed fluctuations are classified into three region, such as low load, middle load and high load region with the variations of the loads. Additionally, as the engine speeds increase and the loads decrease, the analysis of the speed becomes more difficult due to lower variation of the speed. And in all the regions, the main frequency component of the speed fluctuation is firing frequency.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.1
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• pp.34-39
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• 2013

This paper proposes the implementation of robust fuzzy controller for designing intelligent wind farm and mitiagating the fluctuation of wind power generator. The existing researches are limited to individual wind turbine with variable speed so that it is necessary to study the multi-agent wind turbine power system. The scopes of these studies include from the arrangements of each power turbine to the control algorithms for the wind farm. For solving these problems, we introduce the composition of intelligent wind farm and use the T-S (Takagi-Sugeno) fuzzy model which is suitable for designing fuzzy controller. The control object in wind farm enables the minimizing the fluctuation of wind power generator. Simulation results for wind fram which is modelled as mathematically are demonstrated to visualize the feasibility of the proposed method.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.5
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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.