• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.8
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• pp.60-66
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• 2013

The wind-speeds among geographically close wind-farms have high correlations seasonally. This paper presents a novel wind-speed sampling method which sincerely reflects the correlation among wind-speeds of different wind-farms. In the proposed method, the wind-speed samples are generated through the statistical data analysis of the measured past wind-speed data and are adequate to be applied to generation adequacy assessment based on random sampling. In the proposed method, the specific probability distribution need not to be assumed and sufficiently accurate wind-speed samples can be generated based only on the measured past data. The proposed method is applied to the two wind-farm problem to show its applicability.

• Journal of Power Electronics
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• v.9 no.3
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• pp.438-446
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• 2009

The performance of direct torque controlled (DTC) interior permanent magnet (IPM) machines is poor at low speeds due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Due to factors such as forward voltage drop across switching devices in the three phase inverter and dead-time of the devices, the voltage across the machine terminals differ from the reference voltage vector used to estimate stator flux and electromagnetic torque. This can lead to instability of the IPM drive during low speed operation. Compensation schemes for forward voltage drops and dead-time are proposed and implemented in real-time control, resulting in improved performance of the space vector modulated DTC IPM drive, especially at low speeds. No additional hardware is required for these compensators.

• Journal of Information Processing Systems
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• v.6 no.3
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• pp.403-412
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• 2010

Multi-Relay Networks should accommodate mobile users of various speeds. The cellular system should meet the minimum residency time requirements for handover calls while considering an efficient use of available channels. In this paper, we design speed-sensitive handover under dynamic hierarchical cellular systems, in which mobile users are classified according to the mean speed of mobile users and each class has its cellular layer. In order to meet the minimum residency time, the cell size of each cellular layer is dynamically determined depending on the distributions of mean speeds of mobile users. Since the speed-dependent non-preferred cell can provide a secondary resource, overflow and take-back schemes are adopted in the system. We develop analytical models to study the performance of the proposed system, and show that the optimal cell size improves the blocking probability.

• Journal of Environmental Health Sciences
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• v.16 no.2
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• pp.21-29
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• 1990

This study investigated to find out the patterns of the wind direction and wind speeds influenced by concentration of sulfur dioxide in Taegu area for a year in 1988.The results were as follows: Prevailing wind by months where easterly wind from May to September and the other months were westerly and / or west-north-westerly wind. Condition of calm was the most at December(8.6%). Prevailing wind by seasons were westerly and easterly wind in spring and autumn, east-north-easterly and/or west-south wind in summer, the other hand, west-south-westerly and/or west-north-westerly wind in winter. Mean concentration of sulfur dioxide (SO$_{2}$) at each sites were influenced by prevailing wind and location of industrial estates. Mean wind speeds by times were the highest at the before and after 4 P.M.,but the lowest at the before and after 5 A.M. Average wind velocity were highest at Spring (3.38m / sec).

• 연구논문집
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• s.29
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• pp.101-109
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• 1999

Presented in this paper is a new method of identifying the critical speed of rotor-bearing systems without actually reaching at the critical speed itself. Using the method, it is not only possible to calculate the critical speed by measuring a series of rotor responses at much lower rotating speeds away from and without reaching at the critical speeds but also the damping ratio and eccentricity of the system can be identified at the same time. Two types of test rotors were tested on the Rotor Dynamics Test Facility at the Rotordyn-amics Lab, KIMM, and the theory has been confirmed experimentally. The method can be adopted to monitor changes of the dynamic characteristics of critical rotating machinery before and after overhauls, repairs, exchanges of various parts, or to detect trends of direction of subtle changes in the dynamic characteristic parameters over a long periods of time.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.4
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• pp.104-113
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• 2006

To identify aeroelastic characteristics of wings with double-folding mechanism, aeroelastic analyses are performed. There are four wing models which consist of one linear model and three nonlinear models. The nonlinear models have one or two freeplay nonlinearties. The describing function method is used to approximately examine nonlinear effects. The aeroelastic module in MSC/NASTRAN is used to study the aeroelastic characteristics of the considered wing models. The effects of the folding mechanism and amplitude ratio are examined. As the amplitude ratio increases, the flutter speeds approach to those of the wing model with only one nonlinearity. The numerical results show that the flutter speeds of the wings with double-folding mechanism can be lower or higher than those of the wing model with only one folding mechanism depending upon the direction of the second folding mechanism.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.66.5-66
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• 2002

Flatness of strip at aluminum cold rolling is one of the important quality parameters of rolled products. The reasons for this are perhaps obvious: for many of the end uses, subsequent processing requires a flat product poor flatness on-line can lead to reduced running speeds and hence to lower production levels. Amongst the reasons for lower running speeds is the increased risk of strip breaks. The Alcan Ulsan plant developed an automatic flatness control system on conventional four high mills for a year. This system compose of three parts as Intel RMX 3.3 operating system, advanced techniques, and flatness error analysis system. Strip flatness be measured by air bearing roll, passing the s...

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.156-157
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• 2003

A simple method is proposed to split the flux vector of the Euler equations by introducing two artificial wave speeds. The direction of wave propagation can be adjusted by these two wave speeds. This idea greatly simplifies the upwinding, and leads to a new family of upwind schemes. Numerical flux function for multi-dimensional Euler equations is formulated for any grid system, structured or unstructured. A remarkable simplicity of the scheme is that it successfully achieves one-sided approximation for all waves without recourse to any matrix operation. Moreover, its accuracy is comparable with the exact Riemann solver. For 1-D Euler equations, the scheme actually surpasses the exact solver in avoiding expansion shocks without any additional entropy fix. The scheme can exactly resolve stationary contact discontinuities, and it is also freed of the carbuncle problem in multi­dimensional computations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2396-2403
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression method parts was carried out. Simple compression test using grease oil as a lubricant was carried out to characterize flow stress of SMC at elevated temperatures. Two different mold temperatures, $130^{\circ}C{\;}and{\;}150^{\circ}C$ and two different mold speeds, 15, 45 mm/min were used for preparing the specimen of SMC compression molded parts. Surface roughness, tensile, and 3-point bending tests were used to determine the effects of molding temperatures and speeds on mechanical properties of compression molded SMC parts. Orientation and distribution of glass fiber in the compression molded SMC parts were also investigated by photographing the burnt flat specimen and taking SEM(Scanning Electron Microscope) of cross-sectional T-specimen.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.839-842
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• 2002

Some open jet wind tunnels have been operating under limitations due to large pressure fluctuations at some wind tunnel speeds. The Hyundai Aero-acoustic full scale Wind Tunnel (HAWT), which was completed in 1999, shows that most of the specifications were fulfilled but wind tunnel pulsations at some wind speeds were observed. Hyundai Motor Company started the wind tunnel modification in order to solve this problem in 2001. After the modification work the amplitude of pressure fluctuation was reduced and below required level over full wind speed range. Aero-acoustic performance, e.g. background noise, as well as aerodynamic performance were improved after this work.