• Journal of Magnetics
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• v.14 no.4
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• pp.168-171
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• 2009

We propose a new type of spin torque nano-oscillator structure with an exchange- biased free rotating layer. The proposed spin torque nano-oscillator consists of a fixed layer and a free rotating layer with an additional anti-ferromagnetic layer, which leads to an exchange bias in the free rotating layer. The spin dynamics of the exchange-biased free rotating layer can be described as an additional exchange field because the exchange bias manifests itself by the existance of a finite exchange bias field. The exchange bias field plays a similar role to that of a finite external field. Hence, microwave generation can be achieved without an external field in the proposed structure.

• Journal of the Korean Society for Railway
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• v.5 no.4
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• pp.222-230
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• 2002

The rotating bogie frame is used in the bogie for a Light Rail Train under development in Korea. In development of the bogie, the structural strength and fatigue characteristics of the rotating bogie frame have been evaluated under the predefined load cases according to the Korean standards for a urban EMU. No part of the rotating bogie frame was subjected to stress beyond the fatigue endurance limits of the material used when grinding the welding of the lower plate link. It is concluded that the rotating bogie frame is safe in view of its static and fatigure strength.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1046-1050
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• 2000

The necessity of diagnosis of the rotating machinery which is widely used in the industry is increasing. If rotating machinery has fault, we can detect fault using vibration or noise. But, in diagnosing rotating machinery, the end user who doesn't have expert knowledge needs the help of vibration diagnosis expert. However, vibration diagnosis experts who well satisfy the demand of end user are rare. So, this paper propose a development of the case-based reasoning system for abnormal vibration diagnosis of rotating machinery we construct the past experiences of vibration diagnosis expert into case base and shear the experiences of diagnosis expert with the end user. In this paper, we describe that process of structured system and adapting result of abnormal vibration diagnosis of electric motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1513-1520
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• 2000

Complex modal testing method for rotating disks with support motion is introduced which handles the pairs of two point excitation and responses of the disk as complex input and output, respectively. This method utilizes the directivity information and the separation over the rotational speed of forward and backward traveling wave modes or bending coupled modes in the directional frequency response functions(dFRFs). This method synthesizes the normal/reverse dFRFs and complex wave dFRF, which were originally applied to rotating shaft and rotating disk, respectively, and is applied to complex system with dynamically coupled rotating disks and shaft. Experiments with a commercial hard disk drive spindle system demonstrate the validity of this method.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.140-146
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• 2002

High speed rotating machines can be very sensitive to rotating mass unbalance that is a major source of harmful vibration for many types of rotating machinery. So, the balancing procedure is needed for all high-speed rotating system. To save the time and cost of off-line balancing, many researchers have developed the on-line balancing devices and methods. In this paper, an active balancing device, which is an electro-magnetic type, is developed and the active balancing algorithm using influence coefficient method is also proposed. The active balancing experiment for flexible rotors during operation is performed by an active balancing device. As a result, controlled unbalance responses are below the vibration limit at all rotating speed ranges with critical speed.

• Journal of Welding and Joining
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• v.21 no.3
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• pp.40-45
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• 2003

The high-speed rotating arc process forms a flat bead surface with decreased penetration depth because the molten droplets are deflected by centrifugal force. Therefore the rotating arc welding for horizontal fillet welding increases the leg length with the increase of rotation frequency and prevents the deflection of weld bead and overlap. In this study, the relationship between the welding parameters and the weld bead shape - leg length and undercut - are investigated experimentally. Consequently, the weld quality could be improved by rotating arc welding, and sound weld bead was achieved when applied to horizontal fillet welding with 4mm gap by avoiding the undercut which is inevitable for the conventional GMA welding methods.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.8
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• pp.1046-1055
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• 1997

An anisotropic k-.epsilon. turbulence model for predicting the rotating flows is proposed with the simple inclusion of a new parameter dealing with the extra straining effects in the .epsilon.-equation. This model is employed to compute the effects of Coriolis forces on fully-developed flow in a rotating channel. The predicted results indicate that the present model captures fairly well the striking rotational-induced effects on the Reynolds stresses and the mean flow distributions, including the argumentation of turbulent transport on the unstable side (pressure surface) of the channel and its damping on the stable side (suction surface).

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.613-618
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• 2000

It is well known that the rotating motion of a blade-like structure induces centrifugal inertia force that causes the variation of the natural frequencies of the structure. Even though most of blade-like structures can be successfully Idealized as beams, some behave like plates rather than beams. This paper presents a modeling method for the flapwise bending vibration analysis of rotating cantilever plates. The dependence of natural frequencies and free vibration modes on the angular speed as well as the aspect ratio of a rotating plate is investigated. Particularly. the natural frequency loci crossing is observed and discussed In the present study.

• Journal of ILASS-Korea
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• v.14 no.3
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• pp.97-102
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• 2009

The spray characteristics of the high speed rotating fuel injection system were studied. The five variants of rotating fuel nozzle were used by spray test. The diameter of single column injection orifices are varied from 1 mm, 2 mm, 3 mm, 4 mm and 5 mm. We constructed high speed rotating test rig and measured droplet size by PDPA (Phase Doppler Particle Analyzer) system. Also spray was visualized by using high speed camera. In the test results, we could understand that length of liquid column from the injection orifice is mainly controlled by the rotational speeds. SMD is decreased with increasing injection orifice diameter and rotational speeds. Furthermore, from the comparison to the theoritical calculation, we confirmed that SMD is influenced by the liquid film thickness which is formed inner surface of injection orifice.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.9-18
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• 2017

Numerical simulation is carried out for flow characteristics in a plenum fan and the influence of the diameter ratio of the rotating vaneless diffuser on the performance of plenum fan is analyzed. The diameter ratio of the rotating vaneless diffuser employed is from 1.03 to 1.3. The research results show that the rotating vaneless diffuser is able to enhance the performance of plenum fan. It is found that there is significant improvement in static pressure and efficiency at the diameter ratio of 1.05 at high flow coefficients, while the optimal diameter ratio is 1.2 at rated and low flow coefficient.