• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.657-662
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• 2004

This paper presented is a case study of a real compressor rotor of a refinery plant for high speed balancing of flexible rotor. The rotor was tested in the expert high-speed balancing facility established by KIMM at early 2004. The capability of the facility can reach 40000rpm in rotation speed and 8 ton in rotor weight for high-speed balancing. The facility performs multi-plane at-speed balancing using influence coefficient from the vibration data measured at two pedestals. The test rotor had exceeded permissible criteria of vibration at initial run. But by processing a low-speed balancing at 1000 rpm and six trial run trying to calculate influence coefficient of rotor to the range of operating speed, the final result of high-speed balancing revealed a remarkable reduce of vibration at pedestal of the rotor.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.83-86
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• 2002

Numerical simulations are conducted for laminar flow past a sphere rotating In the transverse direction, in order to investigate the effect of the rotation on the characteristics of flow over a sphere. The Reynolds numbers considered are Re=100, 250 and 300 based on the free-stream velocity and the sphere diameter, and the rotational speeds are in the range of $0{\leq}{\omega}{\leq}1$, where ${\omega}^{\ast}$ is the maximum velocity on the sphere surface normalized by the free-stream velocity. At ${\omega}^{\ast}=0$ (without rotation), the flow past the sphere experiences steady axisymmeoy, steady planar-symmetry and unsteady planar-symmetry, respectively, at Re=100, 250 and 300. However, with rotation, the flow becomes planar-symmetric for all the cases investigated and the symmetry plane is orthogonal to the axis of the rotation. The flow is also steady or unsteady depending on both the Reynolds number and the rotational speed, and the vortical structures behind the sphere are significantly modified by the rotation. For example, at Re=300, hairpin vortices completely disappear in the wake at ${\omega}^{\ast}=0.4\;and\;0.6$, and at ${\omega}^{\ast}=1$ vortical structures of a high frequency are newly generated due to the shear layer instability. It is also shown that with increasing rotational speed, the time-averaged drag and lift coefficients increase monotonically.

• Journal of Institute of Control, Robotics and Systems
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• v.10 no.3
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• pp.286-293
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• 2004

This paper presents the result of a study on the starter control for a turbo generator. Because a starter in gear box type turbo-generator system is composed of gearbox and brush DC motor, it should be replaced with High Speed Generator(HSG)) in HSG type Turbo-generator. There-ore, it is necessary to design a new starting algorithm and starter. In gearbox type system, brush DC motor is rotated to the designed speed using low voltage-high current battery power. After brush DC motor speed is increased to several times by gearbox, gas turbine engine can be rotated to designed starting speed. If we implement a starter with High Speed Generator(HSG), it is necessary to drive high-speed generator to high-speed motor. High-speed generator with permanent magnet on rotor has a low leakage inductance fur driving high-speed rotation, and it is necessary high DC link voltage for inverter when High-speed generator is driven to high speed. This paper presents result of development of the boost converter for converting high voltage DC from low battery voltage and design of the inverter for controlling a high frequency current to be injected to motor winding. Also, we show performance of the designed starter by driving the turbo generator.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.788-791
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• 2004

This paper presents a general description of single and dual contact tooling systems, finite element analysis, and discussions on the application of the system to the 5-head router machine which is in particular for aerospace components. This study has been performed as part of the development of the new generation 5-head router machine which is designed for high productivity. Such high productivity in essence requires high speed rotation and multiple spindles in one machine. The high speed rotation may exceed a range in a conventional single contact tooling system. The conventional tooling system is reevaluated in comparison with the dual-contact system. Finite element analysis using simplified spindle models compares major differences in the two systems. Some problems in the application to the 5-head router machine are discussed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.10
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• pp.1371-1376
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• 2014

In this paper, 4-phase switched reluctance motor(SRM) with 8-stator and 6-rotor pole structure is proposed for a high speed fan with a low voltage. The air blower has unidirectional rotation characteristics and requires a low torque ripple and noise as well as high efficiency. To achieve the requirements, voltage and current according to loading condition of limited specification is considered. Design process is to select the bore diameter, pole arc, york of stator and rotor to get a high torque and efficiency. To verify the validity of the proposed structure, finite element method(FEM) is employed to get the performances. And the converter for the proposed SRM is employed a 1.5q power converter for cost effectiveness. Prototype SRM is manufactured and tested, and the test results show this design is within the specification and good for the air blower applications.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2248-2253
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• 2008

A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

• Geomechanics and Engineering
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• v.38 no.5
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• pp.477-486
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• 2024

The process of inspecting and replacing cutting tools in a shield tunnel boring machine (TBM) is called cutterhead intervention (CHI) (Farrokh and Kim 2018). Since CHI is performed by a worker who enters the chamber in TBM, the worker is directly exposed to high water pressure and huge water inflow, especially in areas with high ground water levels, causing health problems for the worker and shortening of available working hours (Kindwall 1990). Ham et al. (2022) proposed a method of reducing the water pressure and water inflow by injecting a grout solution into the ground through the shield TBM chamber, and named it the new face grouting method (NFGM). In this study, the TBM mechanical characteristics including the injection pressure of the grout solution and the cutterhead rotation speed were determined for the best performance of the NFGM. To find the appropriate injection pressure, the water inflow volume according to the injection pressure change was measured by using a water inflow test apparatus. A model torque test apparatus was manufactured to find the appropriate cutterhead rotation speed by investigating the change in the status of the grout solution according to the rotation speed change. In addition, to prove the validity of this study, comprehensive water inflow tests were carried out. The results of the tests showed that the injection pressure equal to overburden pressure + (0.10 ~ 0.15) MPa and the cutterhead rotation speed of 0.8 to 1.0 RPM are the most appropriate. In the actual construction site, it is recommended to select an appropriate value within the proposed range while considering the economic feasibility and workability.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.48-68
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• 2000

The high-speed machining technology of difficult-to-cut material is needed to achieve the high-efficiency of die manufacturing. The high-speed machining is applied in automobile, airplane and electricityㆍelectro industry etc, because it can improve machining efficiency and productivity with high speed, high power and high rotation. In this study, high speed machinability, tool wear characteristics and its monitoring, characteristics of damaged layer, machinability of difficult-to-cut material, characteristics of a free curved surface and method of CAD/CAM system were introduced to acquire the shortening of machining time, the improvement of machining efficiency and the high quality of machined surface. Therefore, we establish the stabilization condition of difficult-to-cut material machining and present the optimal cutting condition for high-efficiency cutting.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.3
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• pp.31-37
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• 2012

This paper presents an efficient hardware architecture to enable the high-speed Givens rotation-based QR decomposition. The proposed architecture achieves a highly parallel givens rotation process by maximizing the number of pivots selected for parallel zero-insertions. Sign-select lookahed (SSL)-CORDIC is also efficiently used for the high-speed givens rotation. The performance of QR decomposition hardware considerably increases compared to the conventional triangular systolic array (TSA) architecture. Moreover, the circuit area of QR decomposition hardware was reduced by decreasing the number of flip-flops for holding the pre-computed results during the decomposition process. The proposed QR decomposition hardware was implemented using TSMC $0.25{\mu}m$ technology. The experimental results show that the proposed architecture achieves up to 70 % speed-up over the TACR/TSA-based architecture for the $8{\times}8$ matrix decomposition.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.12
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• pp.98-105
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• 1997

Image transformation ahs been widely used in compuater graphics, computer vision, robot vision, and image processing. Image rotation is one of important part of image transformation. In image rotation, a two-pass algorithm has many advantages over a one-pass algorithm in high speed computation. This paper presents a new two-pass algorithm that overcomes the limitations of previously reported effect of interpolation. A brief comparison of existent techniques and the twp-pass algorithm newly suggeste is presented. This paper also present the hardware structure for the two-pass algorithm suggested.