• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.83-90
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• 2004

This paper proposes a tool path generation method for machining impellers with 5-axis machining center. The shape of impeller is complex, being composed of pressure surface, suction surface and leading edge, and so on. The compound surface which is made of ruled surface such as pressure surface and suction surface and leading edge such as fillet surface, makes the tool path generation much complicated. To achieve efficient roughing, cutting area is divided into two region and then tool radius of maximum size that do not cause tool intereference is selected for shortening machining time. In finishing, accuracy is improved using side cutting for blade surface and point milling for leading edge.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.61-68
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• 2000

In general, the design of membrane structures takes three steps. The first is shape finding analysis which is determination of initial equilibrium geometry with uniform stresses. The second step involve the computation of the stress-deformation to get completed membrane under various load conditions. The third step is to divide the membrane structures into several plan strips from the initial equilibrium states. This procedure is needed because of the initial shape has usually undevelopable curved surface and is called as "cutting patterns generation". By introducing this work, the deformation due to the initial stress is removed and approximate cutting patterns are generated. In this approach, however, material properties is not considered, therefore the error between the design stresses and actual stresses during the fabrication of plan strips should be occurred. In this paper, actual equilibrium shape analysis procedure for HP shape models is presented. The deviations of stresses between the design stresses and actual stresses are estimated.

• Journal of Mechanical Science and Technology
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• v.14 no.11
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• pp.1244-1249
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• 2000

Burr and shape distortion are two main problems in micro-grooving. In this study, a simplified model is proposed based on large thrust force due to the tool edge radius. Experiments are conducted with a single crystal diamond tool on a 3-axis snaper-like machine varying the depth of cuts, and groove angles on brass, aluminum and OFHC. Experiments have shown that the thrust force becomes a dominant variable in burr generation compared to the principal force when the depth of cut is less than 2${\mu}m$. And fewer burrs develop on more brittle materials. Shape distortion is significant only when the groove angle is small and the depth of cut is larger than 30 ${\mu}m$.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.1
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• pp.33-39
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• 1999

This study has been performed to develop an efficient electrocharged scrubber. To improve collection efficiency of the scrubber, electric-charger was installed at the forefront of the packed crossflow scrubbers, and an experiment of changing discharge electrode shape and fluctuating electric field strength was undertaken. After using a light-oil boiler for generation of particles in the about 80% weight of submicron size particles was exhausted. Collection characteristics of the electrocharged scrubber were similar to those of two-stage electrostatic precipitator. In this study the collection efficiency of submicron size particles has been much improved, compared with the previous ones. In an experiment of changing discharge electrode and electric field strength, a needle-spike shape wire electrode showed a higher collection efficiency than round shape wire. The collection efficiency becomes increased with an increase of electric field strength.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.1
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• pp.49-56
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• 2002

The Z-map is a special farm of discrete non-parametric representation in which the height values at grid points on the xy-plane are stored as a 2D array z[ij]. While the z-map is the simplest farm of representing sculptured surfaces and is the most versatile scheme for modeling non-parametric objects, its practical application in industry (eg, tool-path generation) has aroused much controversy over its weaknesses, namely its inaccuracy, singularity (eg, vertical wall), and some excessive storage needs. Much research or the application of the z-map can be found in various articles, however, research on the systematic analysis of sculptured surface shape representation via the z-map model is rather rare. Presented in this paper are the following: shape modeling power of the simple z-map model, exact (within tolerance) z-map representation of sculptured surfaces which have some feature-shapes such as vertical-walls and real sharp-edges by adopting some complementary z-map models, and some application examples.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.90-101
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• 2004

An inverse mosaic method has been proposed to generate an initial blank shape from the final product shape. Differently from the geometric mapping method, the method can handle triangular patches. However, the generated blank shape is strongly dependent on the order of determination of nodes. In order to compensate the dependency error smoothing technique has been also developed. Although the accuracy has been improved greatly compared with the geometrical mapping method, the method has limitation, due to the no incorporation of plasticity theory. Even though the accuracy of the radius vector method is already proved. the method requires initial guess to start the method. In order to compromise the limitation of the present method and the radius vector method, the method has been connected to the radius vector method. The efficiency of the present optimal blank design method has been verified with some chosen examples.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.180-188
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• 1998

Z-map is a special form of discrete nonparametric representation in which the height values at grid points on the xy-plane are stored as a 2D array z[i.j]. While z-map is the simplest form of representing sculptured surfaces and it is the most versatile scheme for modeling nonparametric objects, its practical application in industry (eg, tool-path generation) aroused much controversy over its weaknesses ; accuracy, singularity (eg, vertical wall), and some excessive storage needs. Although z-map has such limitations, much research on the application of z-map can be found in various articles. However, research on the systematic analysis of sculptured surface shape representation via z-map model is rather rare. Presented in this paper are the following: shape modeling power of the simple z-map model, exact (within tolerance) B-map representation of sculptured surfaces which have some feature-shapes such as vertical-walls and real sharp-edges by adopting some complementary B-map models, and some application examples.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.101-109
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• 2000

Mutual torque ripple in a brushless DC motor is the main source of acoustic noise, especially fur motor operation with high speed and torque. This paper presents a method to obtain mutual torque ripple to identify acoustic noise source. Mutual torque ripple can be determined by analyzing phase current shape and magnetic circuit with different lead angles. Current shape is determined by state space model of voltage equation with the use of inductance calculated by FEM, and confirmed by experimental results. Mutual torque ripple is also determined by FEM analysis for the calculated current shape. Acoustic noise experiment reveals that mutual torque ripple with different lead angle is one of the main sources for noise generation in a brushless DC motor.

• Journal of Power System Engineering
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• v.19 no.1
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• pp.24-30
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• 2015

Geothermal energy is used in various types, such as power generation, direct use, and geothermal heat pumps. Geothermal energy with high temperature have been used for power generation for more than a century. The purpose of the study is to investigate flow and electricity power characteristics of hydraulic turbine for power generation of geothermal heat pump type with closed-system. The differences between the four types of hydraulic turbine, are different from the blade shape, volume, angle and etc. In case of prototype(1), pressure at blade was reduced to 2.1 bar, the kinetic energy of blade increased by increasing flow velocity(4.1 m/s). The increase of flow velocity at the blade edge markedly appeared, to increase the kinetic energy of the rotating shaft. In case that gateway in hydraulic turbine was installed, operating torque and RPM(1,080) of the rotating shaft increased respectively. Although rotational speed of prototype(2) compared to prototype(1) was reduced, the power generation capacity was greater about 3.4 times to 97 W. The most power of 255W was generated from prototype (4).

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.207-211
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• 2000

The mobile communication technology which provides various data service and satifies the required quality in wireless environment can be classified as the forth generation mobile communication technology the forth generation communication technology must has diference with the 2nd and 3nd generation mobile communication technology. It must has the more advanced and more united shape than 3nd generation mobile communication. The forth generation mobile communication technology include following technology: Adaptive coding ar modulation, Smart antenna, Interference cancellation, Advanced handoff mechanism between networks. In this study, I represent the development and standardization of this technology.