• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.438-443
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• 2010

In this paper, behaviors of photonic crystal (PC) radiative structures and antenna arrays have been compared for two types of uniform and binomial excitations. Appropriate duality has been shown between them. These results can be generalized to other types of excitation and arrangement of photonic crystal radiative arrays such as linear, planar and circular arrays of three dimensional (3D) photonic crystal termination resonators. Using these results in designing photonic circuits has some advantages for shaping a particular radiative beam at the photonic crystal exit, for instance reducing the divergence angle of the main lobe in order to enhance the directivity, for better coupling, or for splitting the emitted beam, for dividing the output beam to the next devices in photonic integrated circuits (PIC). For analysis and simulation of the photonic crystal structures, the finite difference time domain (FDTD) method has been employed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1416-1422
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• 2000

The cross-flow fans have been widely used to constitute the air moving systems in many air-ventilating and air-conditioning devices. The cross-flow fan system has many design parameters which have crucial influence on the performance and the noise characteristics of the devices. As a result, there are many difficulties in the design stage of the devices and the general design guide has not been sufficiently established yet. This study presents the experimental results of the parametric investigation of some chosen design parameters, which are the shape of the stabilizer, the profile of the scroll casing, and the diffusion angle of the flow exit. The results are expressed as the fan performance and the specific sound pressure level characteristic. These parts have been found to have crucial effects on the system performance/noise characteristics and should be considered with care in the design stage.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.76-83
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• 2006

Machining accuracy is closely related with tool deflection induced by cutting forces. In this research, cutting forces and tool deflection in end milling are expressed as a closed form of tool rotational angle and cutting conditions. The discrete cutting fores caused by periodic tool entry and exit are represented as a continuous function using the Fourier series expansion. Tool deflection is predicted by direct integration of the distributed loads on cutting edges. Cutting conditions, tool geometry, run-outs and the stiffness of tool clamping part are considered together far cutting forces and tool deflection estimation. Compared with numerical methods, the presented method has advantages in prediction time reduction and the effects of feeding and run-outs on cutting forces and tool deflection can be analyzed quantitatively. This research can be effectively used in real time machining error estimation and cutting condition selection for error minimization since the form accuracy is easily predicted from tool deflection curve.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.210-213
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• 1998

A kinematically admissible velocity field is developed for the analysis of twisting of extruded products. The twisting of extruded product is caused by the linearly increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance and is increased linearly by axial distance from die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increase with the die twisting angle and the aspect ratio of product and friction condition and reduction area and show that angular velocity increases with the decreases in die length.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.111-114
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• 1999

The twisting and extrusion process of the product with involute helical fin from the round billet is developed by the upper bound analysis. The twisting of extruded product is caused by the twisted die surface connecting the die entrance section and the die exit section linearly. In the analysis, the internal shear surface is defined as the curved twisted plane from the taisting of die surface and the shear work is calculated by the consumption of shear energy The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increases with the die twisting angle, the reduction of area, and decreases with the die length, the friction condition.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.3
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• pp.45-52
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• 2006

Burrs formed during face milling operations can be very difficult to characterize since there exist several parameters which have complex combined effects that affect the cutting process. Many researchers have attempted to predict burr characteristics including burr size and shape, using various experimental parameters such as cutting speed, feed rate, in-plane exit angle, and number of inserts. However, the results of these studies tend to be limited to a specific process parameter range and to certain materials. In this paper, the Taguchi method, a systematic optimization method for design and analysis of experiments, is introduced to acquire optimum cutting conditions for burr minimization. In addition, an in process monitoring scheme using an artificial neural network is presented for the prediction of burr types.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.54-59
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• 1999

The purpose of the present study was to develop the numerical method for predicting the on-design and off-design performance of multistage axial-flow compressors. The aerodynamic properties in blade rows were analyzed by incorporating the streamline curvature method as a quasi 3D analysis with the imperical modeling of exit flow angle and loss coefficients. The present calculation procedure has been tested by applying to 5-stage compressors and good agreement with experiments has been found. The detail analysis of aerodynamic performances has been done on the compression part of the bench-scaled gas turbine engines. The predicted performance map at the variable speedline and flow rates could be used as a guide of the engine operation.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.225-229
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• 2000

Burrs formed during face milling operations are very hard to characterize like other machining burrs because there are many parameters which affect the cutting process. Many researchers have tried to predict burr characteristics including burr size and shapes with various experimental conditions such as cutting speed, feed rate, in-plane exit angle, number of inserts, etc., but it still remains as a challenging problem for the complicated combination effects between the parameters. In this paper, Taguchi method, which is a systematic optimization application of design and analysis of experiments, is introduced to acquire optimum cutting parameters for burr minimization. Optimized experimental conditions are provided to show the effectiveness of this approach.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.143-151
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• 1999

The twisting and extrusion process of the product with trapezoidal helical fin from the round billet is developed by the upper bound analysis. The twisting of extruded product is caused by the twisted die surface connecting the die entrance section and the die exit section linearly. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is increased linearly by axial distance from the die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increases with the die twisting angle, the reduction of area, and decreases with the die length, the friction condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.87-96
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• 1989

Flows through impellers of centrifugal compressors are calculated by a streamline curvature method. A method for the exit boundary condition is suggested in the present paper. Flow angles are assumed to be deviated from the blade angle parabolically. The maximum deviation is adjusted for the whole angular momentum to balance with the empirically estimated value by using Stanitz' slip-factor. The present method is verified to reasonably simulate flows through the impeller, when the 3-dimensionality of the flow is not strong. It is also shown that the method can be applied for the design of the splitter in the impeller.