• The Journal of the Acoustical Society of Korea
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• v.15 no.4E
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• pp.3-8
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• 1996

The bubble size distribution is critical information to understand sound propagation and ambient noise in the ocean. To estimate the bubble size distribution in a bubbly water, the sound attenuation has been only in the conventional acoustic bubble sizing method without considering the sound speed variation. However, the effect of the sound speed variation in bubbly water cannot be neglected because of its compressibility variation. The sound attenuation is also affected by the sound speed variation. In this paper, a coherent acoustic bubble sizing inverse technique is introduced as a new bubble sizing technique with considering sound speed variation as well as the sound attenuation. This coherent sizing method is theoretically verified with the bubble distribution functions of single-size, Gaussian, and power-law functions. Its numerical test results with the coherent acoustic bubble sizing method show good agreement with the given bubble distributions.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.2
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• pp.42-50
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• 1995

This paper proposes a new method to investigate combustion phenomena using the variation of crankshaft speed, From the idea that the variation of crankshaft speed contains the information of combustion, the energy method is applied as a single degree of freedom. Through the comparison of measured and calculated crankshaft speed, the proposed energy model is proved to be effective. When the crankshaft speed is used in the energy equation, filtering of the speed is required. The frequency components of cylinder pressure are analyzed and the coefficients of Fourier series above the twelfth frequency of engine speed are considered as a noise. As an example of application of this research, some combustion analyses like mean effective pressure, heat release rate, and misfire detection were carried out.

• Atmosphere
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• v.16 no.3
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• pp.169-185
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• 2006

We have investigated the wind speed variations over the leeward region when the strong wind blows. In this study we employ Envi-met numerical model to simulate the effect of surface boundary conditions. This model is applied for three cases which are characterized by land use and terrain height. The base case having natural geographical condition shows the weakest wind speed around lee side of Chunsudae. The others which remove the vegetation and cut off the terrain above 20 m ASL represent the stronger wind speed than base case. The main factor of this result is the surface friction. The distinct variation of wind is found at offshore area between Chunsudae and the southern part of village, but the northern part where is apart from Chunsudae shows a small variation of wind pattern. The weakening of wind speed around residential area is a maximum of 4~10 m/s when the wind blows in the village as strong as 55 m/s. The gust wind speed is weakened about 7~17 m/s in this case if the coefficient of gust wind adapted as 1.75.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.1
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• pp.59-70
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• 1991

Rupture of lubricant film, thermal characteristics, and variation of viscosity are very important factors to evaluate the performance of journal bearing. Variation of external conditions, load or rotational speed, largely influence these facters. For example, if rotational speed increases lubricant bulk temperature increases and viscosity drops. In this paper the effect of rotational speed variation on the characteristics of lubricant film in a journal bearing is investigated by experiment and theoretical analysis. It has been measured number of lubricant film rupture and lubricant bulk temperature form journal bearing which have been established at the various operating speed of shaft. The range of speed variation is from 900rpm to 2100rpm. Theoretical analysis has been carried out for rupture of lubricant film and thermal characteristics, and these results are compared with experimental results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.200-205
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• 2004

The pantograph for Korean High Speed Train was developed and had been evaluating by through 'G7-R&D project for home grown high speed train technology' In this study, in mechanical aspect, the variation trend of contact force between pantograph and catenary according to the train running speed and driving pattern is conducted. A measuring system for current collecting performance and mechanical characteristics is used for this study, developed and installed on the prototype Korean High Speed Train, and physical characteristics were measured while the KHST runs on the test track. Through this study, remarkable trends of variation are found and analyzed from measured acceleration and vertical contact force between the pan head in pantograph and contact wire in catenary system according to the driving pattern and the train raised a running speed up to 300km/h.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1271-1278
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• 2010

High-speed traction has voltage source variation because the electric power of tractions is supplied by difference traction power system according to operating section. This paper proposes the robust control maintaining constant output performance against voltage source variation for PWM converters of the high speed traction. The proposed scheme consists of feed-forward compensation for current controller by on-line calculating the rms voltage of voltage source. Total dynamic performance of high speed traction can be improved by the reduction of the output voltage ripple which is resulted from voltage source sag and variation. The superior performance and validity of the proposed scheme is proved through the simulation.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.2
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• pp.233-243
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• 1994

Generally, fuzzy PI controller that regulates the gains using fuzzy algorithm shows high performance in speed response. However, it has some problems to the load inertia variation, because the change of speed error(CE) is in a fixed range. As load inertia increases, CE is decreased and the usuage of fuzzy table is limited. Therefore, the output of the fuzzy controller has a limited range. This paper proposes an improved fuzzy PI controller. To reduce the speed overshoot, we adapt a control method that selects a proper CE range with respect to the load inertia variation. The proposed controller is applied to the vector controlled system with 2.2kW induction motor. Some simulation and experimental results are exhibited. With these results, we can easily find that proposed PI controller is more robust than the conventional fuzzy PI controller against the load inertia variation.

• New & Renewable Energy
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• v.7 no.4
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• pp.30-36
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWTs of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system was optimized at higher refrigerant charge amount conditions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.16-21
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• 2011

In machining operation, the quality of surface finish is an important factor for many turned products. In this paper, surface quality in turning machining considering angle variation has been investigated. To reach this goal, surface quality turning experiments are carried out according to cutting conditions with angle variation. The variable cutting conditions are cutting speed, feed rate and taper angle of workpiece. The surface roughness was measured and the effects of cutting conditions were analyzed by the method of analysis of variance (ANOVA). From the experimental results and ANOVA, it is found that a better surface roughness can be obtained as decreasing feed rate, increasing cutting speed. Taper angle variation has been more influenced by feed rate and cutting speed.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.723-730
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• 2006

In the electrical railway, the tension ascension of contact wire is essential to speed up of train and current collection performance of catenary largely depends on the tension. The tension variation rate of the tensioning device used in existing line limits within 5%, and the tension variation rate of the spring-type tensioning device installed at the section where tensioning length is short bounds within 15%. So it is urgent for us to localize it for high speed line, which the tension variation rate is limited within 3%. Therefore in this study, a pulley-type tensioning device for high speed line is developed. To verify the performance of developed device, a performance test, overload test and failure test is carried out under the code of the Kyung-Bu High Speed line. And it is secured durability performance through a fatigue test.