• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1026-1034
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• 2002

This paper describes the development of machining simulation program which is able to design cutter profile and 3-dimensional geometry for rotors in screw compressor. Based on the symmetric rotor profiles developed previously, cutters are designed and 3-dimensional geometries of rotors are generated by using simulation program. Symmetric rotors are manufactured by a universal milling machine, and surface geometries of them are measured by a 3-dimension scanner It is shown that simulation program developed is useful to design cutter for rotor manufacturing and to generate the 3-dimensional helicoid geometry of rotor in screw compressor.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.3
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• pp.353-361
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• 2002

The tip leakage flow passing through the clearance between rotor blade tip and casing shroud has been known to occupy an important portion of the rotor overall loss. In this study, flow characteristics in axial flow rotors with different tip clearances is investigated by experimental and numerical methods. The experimental study was carried out to measure static pressure and velocity profiles at the real rotating test rig. The axial flow rotors used for the experiments have ten blades and three different rotor diameter. The tip clearance heights are 1mm, 3mm, and 4.5mm. Measurements were done using spherical type five-hole probe by non-nulling method. The numerical study was carried out to calculate pressure distributions and velocity vectors at the same condition as the experiments in the flow fields of axial flow rotors using Phoenics code.

• International Journal of Fluid Machinery and Systems
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• v.4 no.2
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• pp.235-242
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• 2011

An application of contra-rotating rotors, in which a rear rotor is in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. One prototype rotors, which we have designed with a conventional method, has given the positive slope of head characteristic curve especially in the rear rotor. It is necessary to understand the internal flow behavior in the rear rotor to establish the design guideline for achieving higher and more reliable performance. In the present study, we carried out the experimental investigations of the internal flow field of the rear rotor, especially at the partial flow rate, by Laser Doppler Velocimetry (LDV) for the main flow and the limiting streamlines observation on rotor surfaces for the boundary layer flows.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.276-287
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• 1990

In this paper research result of transient thermal stress analysis of power plant turbine rotors for life prediction under severs operating conditions is presented. Galerkin's recurrence scheme is used for numerical solution of discretized FEM equation of transient heat conduction equation. Boundary conditions for the equation and operating conditions are intensively investigated for accurate life prediction of turbine rotors in operation. A computer program for on-site application is developed and tested. Distribution of thermal stress in turbine rotors during various operating condition is analyzed with the program and it is found that the peak thermal stress appears during cold stage conditions at the first stage of high pressure rotors.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.866-875
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• 2001

The complex modal testing methods developed for asymmetric rotors are briefly discussed and their performances are experimentally evaluated. For the experiments, a laboratory test rotor is excited by using a newly developed, cost effective magnetic exciter equipped with Hall sensors, which measure the excitation forces. It is concluded that the exciter system is characterized by a wide bandwidth and a high resolution for both the excitation and force measurement, and that the one-exciter/two-sensor technique for complex modal testing of asymmetric rotors is superior to the standard two-exciter/two-sensor technique in terms of practicality and realization.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.581-587
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• 1997

Numerical predictions of aerodynamic noise radiated by subsonic rotors are carried out. A time domain approach for Ffowcs-Williams Hawkings equation of acoustic analogy is used in developing a comprehensive rotor/fan noise prediction program to handle both arbitrary blade shapes and loading conditions. Since only the aeroacoustic aspects of rotors are considered here, the calculations are carried out for rotors with simple aerodynamic characteristics. Broadband noise from ingestion of turbulence is also considered. By incorporating discrete frequency noise prediction of steady loading with broadband spectrum, much better correlation at the low frequency region with experimental data is obtaind. The contributions from different noise mechanisms can also be analysed through this method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1285-1288
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• 2005

Screw rotors, the key parts of screw compressors, are used in compressing air and refrigerant due to their high productivity, compact size, low noise and maintenance. In general, a screw compressor is composed of a pair of rotors of complex geometric shape. The manufacturing cost of the screw rotors is high because the complicated helical shapes of the screw rotors are manufactured usually by the dedicated machine tools. In this study, rotor profile is divided into three parts for the efficient machining. The formed tools are designed and shared for the respective split region. By cutting the screw rotor using the formed tools, this method is more efficient than the end mill in machining rotor. Experimental results show that 4-axis machining using formed tools needs less time and has the accuracy.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.3
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• pp.167-174
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• 2010

The design, dynamics, and control allocation of tri-rotor unmanned aerial vehicles (UAVs) are introduced in this paper. A trirotor UAV has three rotor axes that are equidistant from its center of gravity. Two designs of tri-rotor UAV are introduced in this paper. The single tri-rotor UAV has a servo-motor that is installed on one of the three rotors, which enables rapid control of its motion and its various attitude changes-unlike a quad-rotor UAV that depends only on the angular velocities of four rotors for control. The other design is called 'coaxial tri-rotor UAV,' which has two rotors installed on each rotor axis. Since the tri-rotor type of UAV has the yawing problem induced from an unpaired rotor's reaction torque, it is necessary to derive accurate dynamic and design control logic for both single and coaxial tri-rotors. For that reason, a control strategy is proposed for each type of tri-rotor, and nonlinear simulations of the altitude, Euler angle, and angular velocity responses are conducted by using a classical proportional-integral-derivative controller. Simulation results show that the proposed control strategies are appropriate for the control of single and coaxial tri-rotor UAVs.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.100-105
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• 2008

Cross-drilling on the brake disc is generally known as a way of improving cooling efficiency. In other theories, cross-drilled holes act like a path of gas or water and are also known that they can reduce fading and wetting of brake rotors. However, in disc rotors with cross-drilling, thermal crack phenomena have been reported more frequently and more manufacturing cost should be paid than non cross-drilled disc rotors. In this study, to examine various effects of cross-drilling on the brake disc, two kinds of brake disc rotors, cross-drilled and non cross-drilled, were used in computational fluid dynamic analyses and dynamometer tests.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1383-1392
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• 2009

A disadvantage in the design of a hypotrochoidal gear pump as in a gerotor pump is a lack of parts that can be adjusted to compensate for wear in the rotor set, and as a consequence, it causes a sharp reduction of volumetric efficiency. In this paper, an attempt has been made to reduce the wear rate between the rotors of a hypotrochoidal gear pump. Using the knowledge of shape design on the rotors, the contact stresses without hydrodynamic effect between the rotors' teeth are evaluated through the calculation of the Hertzian contact stress. Based on the above result and the sliding velocity between the rotors, a genetic algorithm (GA) is used as an optimization technique for minimizing the wear rate proportional factor (WRPF). The result shows that the wear rate or the WRPF can be reduced considerably, e.g. approximately 12.8% in this paper, throughout the optimization using GA.