• Journal of computational fluids engineering
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• 제17권2호
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• pp.78-84
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• 2012

Numerical calculations were performed to investigate the influence in aerodynamic characteristics of a rotor system by surrounding structures and the ground effect for the rotor blade on a whirl tower is also investigated. Three dimensional Navier-Stokes simulations were carried out by using unstructured overset mesh technique and parallel computation. The calculated hover performance showed good agreement with the experimental result and showed that the structures around the whirl tower did not affect the aerodynamic characteristics of the blade. The ground effect was studied by comparing with the numerical result for the out of ground condition and the result of an analytic model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제15권7호
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• pp.843-850
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• 2005

In this study, simplified whirl flutter analyses using quasisteady aerodynamic theory have been Performed for a 2-DOF tiIt-rotor system with both pitch and Yaw motions of a rotor-nacelle. The present dynamic system consists of the rotor (propeller) , forming the gyroscopic and aerodynamic element, supported horizontally by a pylon that is pivoted at some wing attachment point. Several design parameters for rotor-nacelle system are considered to practically investigate the effects of whirl flutter stability.

• Proceedings of the KSME Conference
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1136-1141
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• 2008

The helicopter rotor system generates lift, thrust, maneuvering force and moment to the helicopter with the torque and pitch control force transferred from the main rotor hub/control. And the tail rotor system generates the thrust for yaw axis control of the helicopter with the torque and pitch control force transferred from the tail rotor hub/control. Ground whirl test shall be performed to verify the compliance of requirement performance test and dynamic test of rotor blade and hub/control. This paper describes a design of whirl tower test facility for helicopter rotor system test and evaluation. Design results are summarized and compared with design requirements.

• Aerospace Engineering and Technology
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• 제10권2호
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• pp.74-81
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• 2011

A numerical simulation is performed to study the ground effect of a rotating rotor blade on a whirl tower using unstructured overset mesh. The aerodynamic change of the rotor blade by the structure around the whirl tower is also considered. The calculated results showed good agreement with the experiment for the hover performance. The ground effect of the rotor blade is investigated by comparing with the calculated results for the out of ground condition and the results of an analytic model.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 한국화재소방학회 2007년도 춘계학술논문발표회 논문집
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• pp.332-337
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• 2007

• Transactions of the Korean Society for Noise and Vibration Engineering
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• 제23권2호
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• pp.105-111
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• 2013

Whirl tower test is conducted basically during helicopter rotor system development process. And for whirl tower test of rotor hub system, new design blade or existing blade which is remodeled for new rotor hub system is used. Because of simple shape and efficient aerodynamic characteristic, BO-105 helicopter blade is used for helicopter rotor hub development project widely. Originally BO-105 blade is used for hingeless hub system and blade root is used to flexure. So flap stiffness and lag stiffness at blade root area is relatively low compare with airfoil area. So, in order to apply the BO-105 blade to bearingless hub, blade root area have to be reinforced. And in this process, blade root area's section property is changed. In this paper, we suggest reinforcement method of BO-105 blade root area and study dynamic characteristic of bearingless rotor system with reinforcement BO-105 blade.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제28권12호
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• pp.1549-1556
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• 2004

We have deigned, fabricated and compared four different types of static chaos microfluid mixers, including the mixers using straight channel flow, microblock-induced alternating whirl flow, microchannel-induced lamination flow, and combined alternating whirl-lamination flow. Among them, the alternating whirl-lamination (AWL-type) mixer, composed of 3-D rotationally arranged microblocks and dividing microchannels fabricated by conventional planar lithography process, is effective to reduce the mixing length over wide flow rate ranges. We characterize the performance of the fabricated mixers, through the flow visualization technique using phenolphthalein solution. We verify that the AWL-type microfluid mixer shows the shortest fluid mixing length of 2.8mm∼5.8mm for the flow rate range of Re=0.26∼26 with the pressure drop lower than 5kPa. Compared to the previous mixers, requiring the mixing lengths of 7∼17mm, the AWL-type microfluid mixer results in the 60% reduction of the mixing lengths. Due to the reduced mixing lengths within reasonable pressure drop ranges, the present micromixers have potentials for use in the miniaturized Micro-Total-Analysis-Systems($\mu$TAS).

• Journal of the Korea Academia-Industrial cooperation Society
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• 제18권1호
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• pp.238-244
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• 2017

A spindle with a built-in motor can be used to simplify the structure of a machine tool system, but the rotor inevitably has unbalanced mass. This paper presents an analysis of the dynamic behavior. The spindle was used in a CNC lathe and investigated using the finite element method and transfer matrices. The high-speed spindle can be very sensitive to the rotation of an unbalanced mass, which has a harmful effect on many machine tools. Thus, a balancing procedure was performed with a spindle-bearing system for the CNC lathe by numerical analysis. The balancing was performed through the influence coefficient method, and the whirl orbit radii before and after balancing were compared to evaluate the effects. The results show that the rotational speed of the spindle seriously affects the whirl responses of the spindle. The whirl responses were also affected by other factors, such as the unbalanced mass and bearing stiffness. The balancing of the assembled spindle model significantly reduced the whirl orbit magnitude.

• Tribology and Lubricants
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• 제22권6호
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• pp.342-349
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• 2006

In this study, a dynamic behavior of rotor-bearing system used in CNG compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element is formulated including the field element for a shaft section and the point element for roller bearings. The Houbolt method is used to consider the time march for the integration of the system equations. The transient whirl response of rotating shaft supported on roller bearings is obtained, considering compression forces and unbalance forces at eccentric crank-pin part. And, the steady state displacements of the rotor are compared with a variation in stiffness coefficient of roller bearings. Results show that the loci of crankshaft considering unbalance forces and external compression forces are more severe in whirl motion than with only unbalance forces.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.279-284
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• 1999

This paper presents a parametric study and an optimal design of the ER-SFD supporting a rigid rotor system. An attempt is made to obtain the optimal design of an ER-SFD for a two degree-of-freedom rotor model. Such a simple model is used in order to get a better insight into the physics of the problem, A maximum whirl amplitude, supply pressure and voltage are considered, and a maximum whirl amplitude is minimized over a range of speeds and presented for some values of unbalance mass. The results presented in this paper provide important design information necessary to reduce a whirl amplitude of an ER-SFD.